Internet DRAFT - draft-ietf-anima-autonomic-control-plane
draft-ietf-anima-autonomic-control-plane
ANIMA WG T. Eckert, Ed.
Internet-Draft Futurewei USA
Intended status: Standards Track M. Behringer, Ed.
Expires: 3 May 2021
S. Bjarnason
Arbor Networks
30 October 2020
An Autonomic Control Plane (ACP)
draft-ietf-anima-autonomic-control-plane-30
Abstract
Autonomic functions need a control plane to communicate, which
depends on some addressing and routing. This Autonomic Control Plane
should ideally be self-managing, and as independent as possible of
configuration. This document defines such a plane and calls it the
"Autonomic Control Plane", with the primary use as a control plane
for autonomic functions. It also serves as a "virtual out-of-band
channel" for Operations, Administration and Management (OAM)
communications over a network that provides automatically configured
hop-by-hop authenticated and encrypted communications via
automatically configured IPv6 even when the network is not
configured, or misconfigured.
Status of This Memo
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction (Informative) . . . . . . . . . . . . . . . . . 6
1.1. Applicability and Scope . . . . . . . . . . . . . . . . . 9
2. Acronyms and Terminology (Informative) . . . . . . . . . . . 11
3. Use Cases for an Autonomic Control Plane (Informative) . . . 16
3.1. An Infrastructure for Autonomic Functions . . . . . . . . 17
3.2. Secure Bootstrap over a not configured Network . . . . . 17
3.3. Data-Plane Independent Permanent Reachability . . . . . . 17
4. Requirements (Informative) . . . . . . . . . . . . . . . . . 19
5. Overview (Informative) . . . . . . . . . . . . . . . . . . . 20
6. Self-Creation of an Autonomic Control Plane (ACP)
(Normative) . . . . . . . . . . . . . . . . . . . . . . . 21
6.1. Requirements for use of Transport Layer Security (TLS) . 22
6.2. ACP Domain, Certificate and Network . . . . . . . . . . . 23
6.2.1. ACP Certificates . . . . . . . . . . . . . . . . . . 24
6.2.2. ACP Certificate AcpNodeName . . . . . . . . . . . . . 26
6.2.2.1. AcpNodeName ASN.1 Module . . . . . . . . . . . . 29
6.2.3. ACP domain membership check . . . . . . . . . . . . . 30
6.2.3.1. Realtime clock and Time Validation . . . . . . . 33
6.2.4. Trust Anchors (TA) . . . . . . . . . . . . . . . . . 33
6.2.5. Certificate and Trust Anchor Maintenance . . . . . . 34
6.2.5.1. GRASP objective for EST server . . . . . . . . . 35
6.2.5.2. Renewal . . . . . . . . . . . . . . . . . . . . . 37
6.2.5.3. Certificate Revocation Lists (CRLs) . . . . . . . 37
6.2.5.4. Lifetimes . . . . . . . . . . . . . . . . . . . . 38
6.2.5.5. Re-enrollment . . . . . . . . . . . . . . . . . . 38
6.2.5.6. Failing Certificates . . . . . . . . . . . . . . 40
6.3. ACP Adjacency Table . . . . . . . . . . . . . . . . . . . 41
6.4. Neighbor Discovery with DULL GRASP . . . . . . . . . . . 41
6.5. Candidate ACP Neighbor Selection . . . . . . . . . . . . 45
6.6. Channel Selection . . . . . . . . . . . . . . . . . . . . 45
6.7. Candidate ACP Neighbor verification . . . . . . . . . . . 49
6.8. Security Association (Secure Channel) protocols . . . . . 49
6.8.1. General considerations . . . . . . . . . . . . . . . 50
6.8.2. Common requirements . . . . . . . . . . . . . . . . . 51
6.8.3. ACP via IPsec . . . . . . . . . . . . . . . . . . . . 52
6.8.3.1. Native IPsec . . . . . . . . . . . . . . . . . . 52
6.8.3.1.1. RFC8221 (IPsec/ESP) . . . . . . . . . . . . . 53
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6.8.3.1.2. RFC8247 (IKEv2) . . . . . . . . . . . . . . . 54
6.8.3.2. IPsec with GRE encapsulation . . . . . . . . . . 55
6.8.4. ACP via DTLS . . . . . . . . . . . . . . . . . . . . 56
6.8.5. ACP Secure Channel Profiles . . . . . . . . . . . . . 58
6.9. GRASP in the ACP . . . . . . . . . . . . . . . . . . . . 59
6.9.1. GRASP as a core service of the ACP . . . . . . . . . 59
6.9.2. ACP as the Security and Transport substrate for
GRASP . . . . . . . . . . . . . . . . . . . . . . . . 59
6.9.2.1. Discussion . . . . . . . . . . . . . . . . . . . 62
6.10. Context Separation . . . . . . . . . . . . . . . . . . . 63
6.11. Addressing inside the ACP . . . . . . . . . . . . . . . . 63
6.11.1. Fundamental Concepts of Autonomic Addressing . . . . 63
6.11.2. The ACP Addressing Base Scheme . . . . . . . . . . . 65
6.11.3. ACP Zone Addressing Sub-Scheme (ACP-Zone) . . . . . 67
6.11.4. ACP Manual Addressing Sub-Scheme (ACP-Manual) . . . 68
6.11.5. ACP Vlong Addressing Sub-Scheme (ACP-VLong-8/
ACP-VLong-16 . . . . . . . . . . . . . . . . . . . . 69
6.11.6. Other ACP Addressing Sub-Schemes . . . . . . . . . . 70
6.11.7. ACP Registrars . . . . . . . . . . . . . . . . . . . 71
6.11.7.1. Use of BRSKI or other Mechanism/Protocols . . . 71
6.11.7.2. Unique Address/Prefix allocation . . . . . . . . 72
6.11.7.3. Addressing Sub-Scheme Policies . . . . . . . . . 72
6.11.7.4. Address/Prefix Persistence . . . . . . . . . . . 74
6.11.7.5. Further Details . . . . . . . . . . . . . . . . 74
6.12. Routing in the ACP . . . . . . . . . . . . . . . . . . . 74
6.12.1. ACP RPL Profile . . . . . . . . . . . . . . . . . . 75
6.12.1.1. Overview . . . . . . . . . . . . . . . . . . . . 75
6.12.1.1.1. Single Instance . . . . . . . . . . . . . . 75
6.12.1.1.2. Reconvergence . . . . . . . . . . . . . . . 76
6.12.1.2. RPL Instances . . . . . . . . . . . . . . . . . 77
6.12.1.3. Storing vs. Non-Storing Mode . . . . . . . . . . 77
6.12.1.4. DAO Policy . . . . . . . . . . . . . . . . . . . 77
6.12.1.5. Path Metric . . . . . . . . . . . . . . . . . . 77
6.12.1.6. Objective Function . . . . . . . . . . . . . . . 77
6.12.1.7. DODAG Repair . . . . . . . . . . . . . . . . . . 77
6.12.1.8. Multicast . . . . . . . . . . . . . . . . . . . 78
6.12.1.9. Security . . . . . . . . . . . . . . . . . . . . 78
6.12.1.10. P2P communications . . . . . . . . . . . . . . . 78
6.12.1.11. IPv6 address configuration . . . . . . . . . . . 78
6.12.1.12. Administrative parameters . . . . . . . . . . . 79
6.12.1.13. RPL Packet Information . . . . . . . . . . . . . 79
6.12.1.14. Unknown Destinations . . . . . . . . . . . . . . 79
6.13. General ACP Considerations . . . . . . . . . . . . . . . 80
6.13.1. Performance . . . . . . . . . . . . . . . . . . . . 80
6.13.2. Addressing of Secure Channels . . . . . . . . . . . 80
6.13.3. MTU . . . . . . . . . . . . . . . . . . . . . . . . 81
6.13.4. Multiple links between nodes . . . . . . . . . . . . 81
6.13.5. ACP interfaces . . . . . . . . . . . . . . . . . . . 82
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6.13.5.1. ACP loopback interfaces . . . . . . . . . . . . 82
6.13.5.2. ACP virtual interfaces . . . . . . . . . . . . . 84
6.13.5.2.1. ACP point-to-point virtual interfaces . . . 84
6.13.5.2.2. ACP multi-access virtual interfaces . . . . 84
7. ACP support on L2 switches/ports (Normative) . . . . . . . . 87
7.1. Why (Benefits of ACP on L2 switches) . . . . . . . . . . 87
7.2. How (per L2 port DULL GRASP) . . . . . . . . . . . . . . 88
8. Support for Non-ACP Components (Normative) . . . . . . . . . 89
8.1. ACP Connect . . . . . . . . . . . . . . . . . . . . . . . 89
8.1.1. Non-ACP Controller / NMS system . . . . . . . . . . . 90
8.1.2. Software Components . . . . . . . . . . . . . . . . . 92
8.1.3. Auto Configuration . . . . . . . . . . . . . . . . . 93
8.1.4. Combined ACP/Data-Plane Interface (VRF Select) . . . 94
8.1.5. Use of GRASP . . . . . . . . . . . . . . . . . . . . 96
8.2. Connecting ACP islands over Non-ACP L3 networks (Remote ACP
neighbors) . . . . . . . . . . . . . . . . . . . . . . . 97
8.2.1. Configured Remote ACP neighbor . . . . . . . . . . . 97
8.2.2. Tunneled Remote ACP Neighbor . . . . . . . . . . . . 98
8.2.3. Summary . . . . . . . . . . . . . . . . . . . . . . . 98
9. ACP Operations (Informative) . . . . . . . . . . . . . . . . 99
9.1. ACP (and BRSKI) Diagnostics . . . . . . . . . . . . . . . 99
9.1.1. Secure Channel Peer diagnostics . . . . . . . . . . . 103
9.2. ACP Registrars . . . . . . . . . . . . . . . . . . . . . 104
9.2.1. Registrar interactions . . . . . . . . . . . . . . . 104
9.2.2. Registrar Parameter . . . . . . . . . . . . . . . . . 105
9.2.3. Certificate renewal and limitations . . . . . . . . . 106
9.2.4. ACP Registrars with sub-CA . . . . . . . . . . . . . 107
9.2.5. Centralized Policy Control . . . . . . . . . . . . . 107
9.3. Enabling and disabling ACP/ANI . . . . . . . . . . . . . 108
9.3.1. Filtering for non-ACP/ANI packets . . . . . . . . . . 108
9.3.2. Admin Down State . . . . . . . . . . . . . . . . . . 109
9.3.2.1. Security . . . . . . . . . . . . . . . . . . . . 110
9.3.2.2. Fast state propagation and Diagnostics . . . . . 110
9.3.2.3. Low Level Link Diagnostics . . . . . . . . . . . 111
9.3.2.4. Power Consumption Issues . . . . . . . . . . . . 112
9.3.3. Interface level ACP/ANI enable . . . . . . . . . . . 112
9.3.4. Which interfaces to auto-enable? . . . . . . . . . . 112
9.3.5. Node Level ACP/ANI enable . . . . . . . . . . . . . . 114
9.3.5.1. Brownfield nodes . . . . . . . . . . . . . . . . 114
9.3.5.2. Greenfield nodes . . . . . . . . . . . . . . . . 115
9.3.6. Undoing ANI/ACP enable . . . . . . . . . . . . . . . 116
9.3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . 117
9.4. Partial or Incremental adoption . . . . . . . . . . . . . 117
9.5. Configuration and the ACP (summary) . . . . . . . . . . . 118
10. Summary: Benefits (Informative) . . . . . . . . . . . . . . . 119
10.1. Self-Healing Properties . . . . . . . . . . . . . . . . 119
10.2. Self-Protection Properties . . . . . . . . . . . . . . . 121
10.2.1. From the outside . . . . . . . . . . . . . . . . . . 121
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10.2.2. From the inside . . . . . . . . . . . . . . . . . . 122
10.3. The Administrator View . . . . . . . . . . . . . . . . . 123
11. Security Considerations . . . . . . . . . . . . . . . . . . . 124
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 129
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 130
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 130
15. Change log [RFC-Editor: Please remove] . . . . . . . . . . . 131
15.1. Summary of changes since entering IESG review . . . . . 131
15.1.1. Reviews (while in IESG review status) / status . . . 131
15.1.2. BRSKI / ACP registrar related enhancements . . . . . 132
15.1.3. Normative enhancements since start of IESG review . 132
15.1.4. Explanatory enhancements since start of IESG
review . . . . . . . . . . . . . . . . . . . . . . . 133
15.2. draft-ietf-anima-autonomic-control-plane-30 . . . . . . 134
15.3. draft-ietf-anima-autonomic-control-plane-29 . . . . . . 136
15.4. draft-ietf-anima-autonomic-control-plane-28 . . . . . . 138
15.5. draft-ietf-anima-autonomic-control-plane-27 . . . . . . 140
15.6. draft-ietf-anima-autonomic-control-plane-26 . . . . . . 140
15.7. draft-ietf-anima-autonomic-control-plane-25 . . . . . . 141
15.8. draft-ietf-anima-autonomic-control-plane-24 . . . . . . 144
15.9. draft-ietf-anima-autonomic-control-plane-23 . . . . . . 145
15.10. draft-ietf-anima-autonomic-control-plane-22 . . . . . . 146
16. Normative References . . . . . . . . . . . . . . . . . . . . 148
17. Informative References . . . . . . . . . . . . . . . . . . . 151
Appendix A. Background and Futures (Informative) . . . . . . . . 160
A.1. ACP Address Space Schemes . . . . . . . . . . . . . . . . 160
A.2. BRSKI Bootstrap (ANI) . . . . . . . . . . . . . . . . . . 161
A.3. ACP Neighbor discovery protocol selection . . . . . . . . 162
A.3.1. LLDP . . . . . . . . . . . . . . . . . . . . . . . . 162
A.3.2. mDNS and L2 support . . . . . . . . . . . . . . . . . 163
A.3.3. Why DULL GRASP . . . . . . . . . . . . . . . . . . . 163
A.4. Choice of routing protocol (RPL) . . . . . . . . . . . . 163
A.5. ACP Information Distribution and multicast . . . . . . . 165
A.6. CAs, domains and routing subdomains . . . . . . . . . . . 166
A.7. Intent for the ACP . . . . . . . . . . . . . . . . . . . 167
A.8. Adopting ACP concepts for other environments . . . . . . 168
A.9. Further (future) options . . . . . . . . . . . . . . . . 170
A.9.1. Auto-aggregation of routes . . . . . . . . . . . . . 170
A.9.2. More options for avoiding IPv6 Data-Plane
dependencies . . . . . . . . . . . . . . . . . . . . 170
A.9.3. ACP APIs and operational models (YANG) . . . . . . . 171
A.9.4. RPL enhancements . . . . . . . . . . . . . . . . . . 171
A.9.5. Role assignments . . . . . . . . . . . . . . . . . . 172
A.9.6. Autonomic L3 transit . . . . . . . . . . . . . . . . 172
A.9.7. Diagnostics . . . . . . . . . . . . . . . . . . . . . 172
A.9.8. Avoiding and dealing with compromised ACP nodes . . . 173
A.9.9. Detecting ACP secure channel downgrade attacks . . . 174
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Appendix B. Unfinished considerations (To Be Removed From
RFC) . . . . . . . . . . . . . . . . . . . . . . . . . . 175
B.1. Considerations for improving secure channel
negotiation . . . . . . . . . . . . . . . . . . . . . . . 175
B.2. ACP address verification . . . . . . . . . . . . . . . . 176
B.3. Public CA considerations . . . . . . . . . . . . . . . . 178
B.4. Hardening DULL GRASP considerations . . . . . . . . . . . 179
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 179
1. Introduction (Informative)
Autonomic Networking is a concept of self-management: Autonomic
functions self-configure, and negotiate parameters and settings
across the network. [RFC7575] defines the fundamental ideas and
design goals of Autonomic Networking. A gap analysis of Autonomic
Networking is given in [RFC7576]. The reference architecture for
Autonomic Networking in the IETF is specified in the document
[I-D.ietf-anima-reference-model].
Autonomic functions need an autonomically built communications
infrastructure. This infrastructure needs to be secure, resilient
and re-usable by all autonomic functions. Section 5 of [RFC7575]
introduces that infrastructure and calls it the Autonomic Control
Plane (ACP). More descriptively it would be the "Autonomic
communications infrastructure for OAM and Control". For naming
consistency with that prior document, this document continues to use
the name ACP though.
Today, the OAM and control plane of IP networks is what is typically
called in-band management/signaling: Its management and control
protocol traffic depends on the routing and forwarding tables,
security, policy, QoS and potentially other configuration that first
has to be established through the very same management and control
protocols. Misconfigurations including unexpected side effects or
mutual dependences can disrupt OAM and control operations and
especially disrupt remote management access to the affected node
itself and potentially a much larger number of nodes for whom the
affected node is on the network path.
For an example of inband management failing in the face of operator
induced misconfiguration, see [FCC], for example III.B.15 on page 8:
"...engineers almost immediately recognized that they had
misdiagnosed the problem. However, they were unable to resolve the
issue by restoring the link because the network management tools
required to do so remotely relied on the same paths they had just
disabled".
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Traditionally, physically separate, so-called out-of-band
(management) networks have been used to avoid these problems or at
least to allow recovery from such problems. Worst case, personnel
are sent on site to access devices through out-of-band management
ports (also called craft ports, serial console, management ethernet
port). However, both options are expensive.
In increasingly automated networks either centralized management
systems or distributed autonomic service agents in the network
require a control plane which is independent of the configuration of
the network they manage, to avoid impacting their own operations
through the configuration actions they take.
This document describes a modular design for a self-forming, self-
managing and self-protecting ACP, which is a virtual out-of-band
network designed to be as independent as possible of configuration,
addressing and routing to avoid the self-dependency problems of
current IP networks while still operating in-band on the same
physical network that it is controlling and managing. The ACP design
is therefore intended to combine as well as possible the resilience
of out-of-band management networks with the low-cost of traditional
IP in-band network management. The details how this is achieved are
described in Section 6.
In a fully autonomic network node without legacy control or
management functions/protocols, the Data-Plane would be for example
just a forwarding plane for "Data" IPv6 packets, aka: packets other
than the control and management plane packets that are forwarded by
the ACP itself. In such networks/nodes, there would be no non-
autonomous control or non-autonomous management plane.
Routing protocols for example would be built inside the ACP as so-
called autonomous functions via autonomous service agents, leveraging
the ACP's functions instead of implementing them separately for each
protocol: discovery, automatically established authenticated and
encrypted local and distant peer connectivity for control and
management traffic, and common control/management protocol session
and presentation functions.
When ACP functionality is added to nodes that have non-autonomous
management plane and/or control plane functions (henceforth called
non-autonomous nodes), the ACP instead is best abstracted as a
special Virtual Routing and Forwarding (VRF) instance (or virtual
router) and the complete pre-existing non-autonomous management and/
or control plane is considered to be part of the Data-Plane to avoid
introduction of more complex, new terminology only for this case.
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Like the forwarding plane for "Data" packets, the non-autonomous
control and management plane functions can then be managed/used via
the ACP. This terminology is consistent with pre-existing documents
such as [RFC8368].
In both instances (autonomous and non-autonomous nodes), the ACP is
built such that it is operating in the absence of the Data-Plane, and
in the case of existing non-autonomous (management, control)
components in the Data-Plane also in the presence of any
(mis-)configuration thereof.
The Autonomic Control Plane serves several purposes at the same time:
1. Autonomic functions communicate over the ACP. The ACP therefore
directly supports Autonomic Networking functions, as described in
[I-D.ietf-anima-reference-model]. For example, Generic Autonomic
Signaling Protocol (GRASP - [I-D.ietf-anima-grasp]) runs securely
inside the ACP and depends on the ACP as its "security and
transport substrate".
2. A controller or network management system can use it to securely
bootstrap network devices in remote locations, even if the (Data-
Plane) network in between is not yet configured; no Data-Plane
dependent bootstrap configuration is required. An example of
such a secure bootstrap process is described in
[I-D.ietf-anima-bootstrapping-keyinfra].
3. An operator can use it to access remote devices using protocols
such as Secure SHell (SSH) or Network Configuration Protocol
(NETCONF) running across the ACP, even if the network is
misconfigured or not configured.
This document describes these purposes as use cases for the ACP in
Section 3, it defines the requirements in Section 4. Section 5 gives
an overview of how the ACP is constructed.
The normative part of this document starts with Section 6, where the
ACP is specified. Section 7 explains how to support ACP on L2
switches (normative). Section 8 explains how non-ACP nodes and
networks can be integrated (normative).
The remaining sections are non-normative: Section 10 reviews benefits
of the ACP (after all the details have been defined), Section 9
provides operational recommendations, Appendix A provides additional
explanations and describes additional details or future standard or
proprietary extensions that were considered not to be appropriate for
standardization in this document but were considered important to
document. There are no dependencies against Appendix A to build a
complete working and interoperable ACP according to this document.
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The ACP provides secure IPv6 connectivity, therefore it can be used
not only as the secure connectivity for self-management as required
for the ACP in [RFC7575], but it can also be used as the secure
connectivity for traditional (centralized) management. The ACP can
be implemented and operated without any other components of autonomic
networks, except for the GRASP protocol. ACP relies on per-link DULL
GRASP (see Section 6.4) to autodiscover ACP neighbors, and includes
the ACP GRASP instance to provide service discovery for clients of
the ACP (see Section 6.9) including for its own maintenance of ACP
certificates.
The document "Using Autonomic Control Plane for Stable Connectivity
of Network OAM" [RFC8368] describes how the ACP alone can be used to
provide secure and stable connectivity for autonomic and non-
autonomic OAM applications, specifically for the case of current non-
autonomic networks/nodes. That document also explains how existing
management solutions can leverage the ACP in parallel with
traditional management models, when to use the ACP and how to
integrate with potentially IPv4 only OAM backends.
Combining ACP with Bootstrapping Remote Secure Key Infrastructures
(BRSKI), see [I-D.ietf-anima-bootstrapping-keyinfra]) results in the
"Autonomic Network Infrastructure" (ANI) as defined in
[I-D.ietf-anima-reference-model], which provides autonomic
connectivity (from ACP) with secure zero-touch (automated) bootstrap
from BRSKI. The ANI itself does not constitute an Autonomic Network,
but it allows the building of more or less autonomic networks on top
of it - using either centralized, Software Defined Networking-
(SDN-)style (see [RFC7426]) automation or distributed automation via
Autonomic Service Agents (ASA) / Autonomic Functions (AF) - or a
mixture of both. See [I-D.ietf-anima-reference-model] for more
information.
1.1. Applicability and Scope
Please see the following Terminology section (Section 2) for
explanations of terms used in this section.
The design of the ACP as defined in this document is considered to be
applicable to all types of "professionally managed" networks: Service
Provider, Local Area Network (LAN), Metro(politan networks), Wide
Area Network (WAN), Enterprise Information Technology (IT) and
->"Operational Technology" (OT) networks. The ACP can operate
equally on layer 3 equipment and on layer 2 equipment such as bridges
(see Section 7). The hop-by-hop authentication, integrity-protection
and confidentiality mechanism used by the ACP is defined to be
negotiable, therefore it can be extended to environments with
different protocol preferences. The minimum implementation
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requirements in this document attempt to achieve maximum
interoperability by requiring support for multiple options depending
on the type of device: IPsec, see [RFC4301], and Datagram Transport
Layer Security (DTLS, see Section 6.8.4).
The implementation footprint of the ACP consists of Public Key
Infrastructure (PKI) code for the ACP certificate including
"Enrollment over Secure Transport (EST, see [RFC7030]), the GRASP
protocol, UDP, TCP and Transport Layer Security (TLS, see
Section 6.1), for security and reliability of GRASP and for EST, the
ACP secure channel protocol used (such as IPsec or DTLS), and an
instance of IPv6 packet forwarding and routing via the Routing
Protocol for Low-power and Lossy Networks (RPL), see [RFC6550], that
is separate from routing and forwarding for the Data-Plane (user
traffic).
The ACP uses only IPv6 to avoid complexity of dual-stack ACP
operations (IPv6/IPv4). Nevertheless, it can without any changes be
integrated into even otherwise IPv4-only network devices. The Data-
Plane itself would not need to change and it could continue to be
IPv4 only. For such IPv4-only devices, the IPv6 protocol itself
would be additional implementation footprint that is only required
for the ACP.
The protocol choices of the ACP are primarily based on wide use and
support in networks and devices, well understood security properties
and required scalability. The ACP design is an attempt to produce
the lowest risk combination of existing technologies and protocols to
build a widely applicable operational network management solution.
RPL was chosen because it requires a smaller routing table footprint
in large networks compared to other routing protocols with an
autonomically configured single area. The deployment experience of
large scale Internet of Things (IoT) networks serves as the basis for
wide deployment experience with RPL. The profile chosen for RPL in
the ACP does not leverage any RPL specific forwarding plane features
(IPv6 extension headers), making its implementation a pure control
plane software requirement.
GRASP is the only completely novel protocol used in the ACP, and this
choice was necessary because there is no existing suitable protocol
to provide the necessary functions to the ACP, so GRASP was developed
to fill that gap.
The ACP design can be applicable to devices constrained with respect
to cpu and memory, and to networks constrained with respect to
bitrate and reliability, but this document does not attempt to define
the most constrained type of devices or networks to which the ACP is
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applicable. RPL and DTLS for ACP secure channels are two protocol
choices already making ACP more applicable to constrained
environments. Support for constrained devices in this specification
is opportunistic, but not complete, because the reliable transport
for GRASP (see Section 6.9.2) only specifies TCP/TLS. See
Appendix A.8 for discussions about how future standards or
proprietary extensions/variations of the ACP could better meet
different expectations from those on which the current design is
based including supporting constrained devices better.
2. Acronyms and Terminology (Informative)
[RFC-Editor: Please add ACP, BRSKI, GRASP, MASA to https://www.rfc-
editor.org/materials/abbrev.expansion.txt.]
[RFC-Editor: What is the recommended way to reference a hanging text,
e.g. to a definition in the list of definitions? Up to -28, this
document was using XMLv2 and the only option I could find for RFC/XML
to point to a hanging text was format="title", which leads to
references such as '->"ACP certificate" ()', aka: redundant empty
parenthesis. Many reviewers where concerned about this. I created a
ticket to ask for an xml2rfc enhancement to avoid this in the future:
https://trac.tools.ietf.org/tools/xml2rfc/trac/ticket/347. When i
changed to XMLv3 in version -29, i could get rid of the unnecessary
() by using format="none", but that format is declared to be
deprecated in XMLv3. So i am not aware of any working AND "non-
deprecated" option.]
[RFC-Editor: Question: Is it possible to change the first occurrences
of [RFCxxxx] references to "rfcxxx title" [RFCxxxx]? the XML2RFC
format does not seem to offer such a format, but I did not want to
duplicate 50 first references - one reference for title mentioning
and one for RFC number.]
This document serves both as a normative specification for how ACP
nodes have to behave as well as describing requirements, benefits,
architecture and operational aspects to explain the context.
Normative sections are labelled "(Normative)" and use BCP 14
keywords. Other sections are labelled "(Informative)" and do not use
those normative keywords.
In the rest of the document we will refer to systems using the ACP as
"nodes". Typically, such a node is a physical (network equipment)
device, but it can equally be some virtualized system. Therefore, we
do not refer to them as devices unless the context specifically calls
for a physical system.
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This document introduces or uses the following terms (sorted
alphabetically). Terms introduced are explained on first use, so
this list is for reference only.
ACP: "Autonomic Control Plane". The Autonomic Function as defined
in this document. It provides secure zero-touch (automated)
transitive (network wide) IPv6 connectivity for all nodes in the
same ACP domain as well as a GRASP instance running across this
ACP IPv6 connectivity. The ACP is primarily meant to be used as a
component of the ANI to enable Autonomic Networks but it can
equally be used in simple ANI networks (with no other Autonomic
Functions) or completely by itself.
ACP address: An IPv6 address assigned to the ACP node. It is stored
in the acp-node-name of the ->"ACP certificate".
ACP address range/set: The ACP address may imply a range or set of
addresses that the node can assign for different purposes. This
address range/set is derived by the node from the format of the
ACP address called the "addressing sub-scheme".
ACP connect interface: An interface on an ACP node providing access
to the ACP for non ACP capable nodes without using an ACP secure
channel. See Section 8.1.1.
ACP domain: The ACP domain is the set of nodes with ->"ACP
certificates" that allow them to authenticate each other as
members of the ACP domain. See also Section 6.2.3.
ACP (ANI/AN) certificate: A [RFC5280] certificate (LDevID) carrying
the acp-node-name which is used by the ACP to learn its address in
the ACP and to derive and cryptographically assert its membership
in the ACP domain.
ACP acp-node-name field: An information field in the ACP certificate
in which the ACP relevant information is encoded: the ACP domain
name, the ACP IPv6 address of the node and optional additional
role attributes about the node.
ACP Loopback interface: The Loopback interface in the ACP Virtual
Routing and Forwarding (VRF) that has the ACP address assigned to
it. See Section 6.13.5.1.
ACP network: The ACP network constitutes all the nodes that have
access to the ACP. It is the set of active and transitively
connected nodes of an ACP domain plus all nodes that get access to
the ACP of that domain via ACP edge nodes.
ACP (ULA) prefix(es): The /48 IPv6 address prefixes used across the
ACP. In the normal/simple case, the ACP has one ULA prefix, see
Section 6.11. The ACP routing table may include multiple ULA
prefixes if the "rsub" option is used to create addresses from
more than one ULA prefix. See Section 6.2.2. The ACP may also
include non-ULA prefixes if those are configured on ACP connect
interfaces. See Section 8.1.1.
ACP secure channel: A channel authenticated via ->"ACP certificates"
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providing integrity protection and confidentiality through
encryption. These are established between (normally) adjacent ACP
nodes to carry traffic of the ACP VRF securely and isolated from
Data-Plane traffic in-band over the same link/path as the Data-
Plane.
ACP secure channel protocol: The protocol used to build an ACP
secure channel, e.g., Internet Key Exchange Protocol version 2
(IKEv2) with IPsec or Datagram Transport Layer Security (DTLS).
ACP virtual interface: An interface in the ACP VRF mapped to one or
more ACP secure channels. See Section 6.13.5.
AN "Autonomic Network": A network according to
[I-D.ietf-anima-reference-model]. Its main components are ANI,
Autonomic Functions and Intent.
(AN) Domain Name: An FQDN (Fully Qualified Domain Name) in the acp-
node-name of the Domain Certificate. See Section 6.2.2.
ANI (nodes/network): "Autonomic Network Infrastructure". The ANI is
the infrastructure to enable Autonomic Networks. It includes ACP,
BRSKI and GRASP. Every Autonomic Network includes the ANI, but
not every ANI network needs to include autonomic functions beyond
the ANI (nor Intent). An ANI network without further autonomic
functions can for example support secure zero-touch (automated)
bootstrap and stable connectivity for SDN networks - see
[RFC8368].
ANIMA: "Autonomic Networking Integrated Model and Approach". ACP,
BRSKI and GRASP are specifications of the IETF ANIMA working
group.
ASA: "Autonomic Service Agent". Autonomic software modules running
on an ANI device. The components making up the ANI (BRSKI, ACP,
GRASP) are also described as ASAs.
Autonomic Function: A function/service in an Autonomic Network (AN)
composed of one or more ASA across one or more ANI nodes.
BRSKI: "Bootstrapping Remote Secure Key Infrastructures"
([I-D.ietf-anima-bootstrapping-keyinfra]. A protocol extending
EST to enable secure zero-touch bootstrap in conjunction with ACP.
ANI nodes use ACP, BRSKI and GRASP.
CA: "Certification Authority". An entity that issues digital
certificates. A CA uses its private key to sign the certificates
it issues. Relying parties use the public key in the CA
certificate to validate the signature.
CRL: "Certificate Revocation List". A list of revoked certificates.
Required to revoke certificates before their lifetime expires.
Data-Plane: The counterpoint to the ACP VRF in an ACP node:
forwarding of user traffic and in non-autonomous nodes/networks
also any non-autonomous control and/or management plane functions.
In a fully Autonomic Network node, the Data-Plane is managed
autonomically via Autonomic Functions and Intent. See Section 1
for more detailed explanations.
device: A physical system, or physical node.
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Enrollment: The process through which a node authenticates itself to
a network with an initial identity, which is often called IDevID
certificate, and acquires from the network a network specific
identity, which is often called LDevID certificate, and
certificates of one or more Trust Anchor(s). In the ACP, the
LDevID certificate is called the ACP certificate.
EST: "Enrollment over Secure Transport" ([RFC7030]). IETF standard-
track protocol for enrollment of a node with an LDevID
certificate. BRSKI is based on EST.
GRASP: "Generic Autonomic Signaling Protocol". An extensible
signaling protocol required by the ACP for ACP neighbor discovery.
The ACP also provides the "security and transport substrate" for
the "ACP instance of GRASP". This instance of GRASP runs across
the ACP secure channels to support BRSKI and other NOC/OAM or
Autonomic Functions. See [I-D.ietf-anima-grasp].
IDevID: An "Initial Device IDentity" X.509 certificate installed by
the vendor on new equipment. Contains information that
establishes the identity of the node in the context of its vendor/
manufacturer such as device model/type and serial number. See
[AR8021]. The IDevID certificate cannot be used as a node
identifier for the ACP because they are not provisioned by the
owner of the network, so they can not directly indicate an ACP
domain they belong to.
in-band (management/signaling): In-band management traffic and/or
control plane signaling uses the same network resources such as
routers/switches and network links that it manages/controls. In-
band is the standard management and signaling mechanism in IP
networks. Compared to ->"out-of-band" it requires no additional
physical resources, but introduces potentially circular
dependencies for its correct operations. See ->"introduction".
Intent: Policy language of an autonomic network according to
[I-D.ietf-anima-reference-model].
Loopback interface: See ->"ACP Loopback interface".
LDevID: A "Local Device IDentity" is an X.509 certificate installed
during "enrollment". The Domain Certificate used by the ACP is an
LDevID certificate. See [AR8021].
Management: Used in this document as another word for ->"OAM".
MASA (service): "Manufacturer Authorized Signing Authority". A
vendor/manufacturer or delegated cloud service on the Internet
used as part of the BRSKI protocol.
MIC: "Manufacturer Installed Certificate". This is another word to
describe an IDevID in referenced materials. This term is not used
in this document.
native interface: Interfaces existing on a node without
configuration of the already running node. On physical nodes
these are usually physical interfaces; on virtual nodes their
equivalent.
NOC: Network Operations Center.
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node: A system supporting the ACP according to this document. Can
be virtual or physical. Physical nodes are called devices.
Node-ID: The identifier of an ACP node inside that ACP. It is the
last 64 (see Section 6.11.3) or 78-bits (see Section 6.11.5) of
the ACP address.
OAM: Operations, Administration and Management. Includes Network
Monitoring.
Operational Technology (OT): https://en.wikipedia.org/wiki/
Operational_Technology: "The hardware and software dedicated to
detecting or causing changes in physical processes through direct
monitoring and/or control of physical devices such as valves,
pumps, etc.". OT networks are today in most cases well separated
from Information Technology (IT) networks.
out-of-band (management) network: An out-of-band network is a
secondary network used to manage a primary network. The equipment
of the primary network is connected to the out-of-band network via
dedicated management ports on the primary network equipment.
Serial (console) management ports were historically most common,
higher end network equipment now also has ethernet ports dedicated
only for management. An out-of-band network provides management
access to the primary network independent of the configuration
state of the primary network. See ->"Introduction"
(virtual) out-of-band network: The ACP can be called a virtual out-
of-band network for management and control because it attempts to
provide the benefits of a (physical) ->"out-of-band network" even
though it is physically carried ->"in-band". See
->"introduction".
root CA: "root Certification Authority". A ->"CA" for which the
root CA Key update procedures of [RFC7030], Section 4.4 can be
applied.
RPL: "IPv6 Routing Protocol for Low-Power and Lossy Networks". The
routing protocol used in the ACP. See [RFC6550].
(ACP/ANI/BRSKI) Registrar: An ACP registrar is an entity (software
and/or person) that is orchestrating the enrollment of ACP nodes
with the ACP certificate. ANI nodes use BRSKI, so ANI registrars
are also called BRSKI registrars. For non-ANI ACP nodes, the
registrar mechanisms are undefined by this document. See
Section 6.11.7. Renewal and other maintenance (such as
revocation) of ACP certificates may be performed by other entities
than registrars. EST must be supported for ACP certificate
renewal (see Section 6.2.5). BRSKI is an extension of EST, so
ANI/BRSKI registrars can easily support ACP domain certificate
renewal in addition to initial enrollment.
RPI: "RPL Packet Information". Network extension headers for use
with the ->"RPL" routing protocols. Not used with RPL in the ACP.
See Section 6.12.1.13.
RPL: "Routing Protocol for Low-Power and Lossy Networks". The
routing protocol used in the ACP. See Section 6.12.
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sUDI: "secured Unique Device Identifier". This is another word to
describe an IDevID in referenced material. This term is not used
in this document.
TA: "Trust Anchor". A Trust Anchor is an entity that is trusted for
the purpose of certificate validation. Trust Anchor Information
such as self-signed certificate(s) of the Trust Anchor is
configured into the ACP node as part of Enrollment. See
[RFC5280], Section 6.1.1.
UDI: "Unique Device Identifier". In the context of this document
unsecured identity information of a node typically consisting of
at least device model/type and serial number, often in a vendor
specific format. See sUDI and LDevID.
ULA: (Global ID prefix) A "Unique Local Address" (ULA) is an IPv6
address in the block fc00::/7, defined in [RFC4193]. ULA is the
IPv6 successor of the IPv4 private address space ([RFC1918]). ULA
have important differences over IPv4 private addresses that are
beneficial for and exploited by the ACP, such as the Locally
Assigned Global ID prefix, which are the first 48-bits of a ULA
address [RFC4193], section 3.2.1. In this document this prefix is
abbreviated as "ULA prefix".
(ACP) VRF: The ACP is modeled in this document as a "Virtual Routing
and Forwarding" instance (VRF). This means that it is based on a
"virtual router" consisting of a separate IPv6 forwarding table to
which the ACP virtual interfaces are attached and an associated
IPv6 routing table separate from the Data-Plane. Unlike the VRFs
on MPLS/VPN-PE ([RFC4364]) or LISP XTR ([RFC6830]), the ACP VRF
does not have any special "core facing" functionality or routing/
mapping protocols shared across multiple VRFs. In vendor products
a VRF such as the ACP-VRF may also be referred to as a so called
VRF-lite.
(ACP) Zone: An ACP zone is a set of ACP nodes using the same zone
field value in their ACP address according to Section 6.11.3.
Zones are a mechanism to support structured addressing of ACP
addresses within the same /48-bit ULA prefix.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119],[RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Use Cases for an Autonomic Control Plane (Informative)
This section summarizes the use cases that are intended to be
supported by an ACP. To understand how these are derived from and
relate to the larger set of use cases for autonomic networks, please
refer to [RFC8316].
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3.1. An Infrastructure for Autonomic Functions
Autonomic Functions need a stable infrastructure to run on, and all
autonomic functions should use the same infrastructure to minimize
the complexity of the network. In this way, there is only need for a
single discovery mechanism, a single security mechanism, and single
instances of other processes that distributed functions require.
3.2. Secure Bootstrap over a not configured Network
Today, bootstrapping a new node typically requires all nodes between
a controlling node such as an SDN controller ("Software Defined
Networking", see [RFC7426]) and the new node to be completely and
correctly addressed, configured and secured. Bootstrapping and
configuration of a network happens in rings around the controller -
configuring each ring of devices before the next one can be
bootstrapped. Without console access (for example through an out-of-
band network) it is not possible today to make devices securely
reachable before having configured the entire network leading up to
them.
With the ACP, secure bootstrap of new devices and whole new networks
can happen without requiring any configuration of unconfigured
devices along the path: As long as all devices along the path support
ACP and a zero-touch bootstrap mechanism such as BRSKI, the ACP
across a whole network of unconfigured devices can be brought up
without operator/provisioning intervention. The ACP also provides
additional security for any bootstrap mechanism, because it can
provide encrypted discovery (via ACP GRASP) of registrars or other
bootstrap servers by bootstrap proxies connecting to nodes that are
to be bootstrapped and the ACP encryption hides the identities of the
communicating entities (pledge and registrar), making it more
difficult to learn which network node might be attackable. The ACP
certificate can also be used to end-to-end encrypt the bootstrap
communication between such proxies and server. Note that
bootstrapping here includes not only the first step that can be
provided by BRSKI (secure keys), but also later stages where
configuration is bootstrapped.
3.3. Data-Plane Independent Permanent Reachability
Today, most critical control plane protocols and OAM protocols are
using the Data-Plane of the network. This leads to often undesirable
dependencies between control and OAM plane on one side and the Data-
Plane on the other: Only if the forwarding and control plane of the
Data-Plane are configured correctly, will the Data-Plane and the OAM/
control plane work as expected.
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Data-Plane connectivity can be affected by errors and faults, for
example misconfigurations that make AAA (Authentication,
Authorization and Accounting) servers unreachable or can lock an
administrator out of a device; routing or addressing issues can make
a device unreachable; shutting down interfaces over which a current
management session is running can lock an admin irreversibly out of
the device. Traditionally only out-of-band access can help recover
from such issues (such as serial console or ethernet management
port).
Data-Plane dependencies also affect applications in a Network
Operations Center (NOC) such as SDN controller applications: Certain
network changes are today hard to implement, because the change
itself may affect reachability of the devices. Examples are address
or mask changes, routing changes, or security policies. Today such
changes require precise hop-by-hop planning.
Note that specific control plane functions for the Data-Plane often
want to depend on forwarding of their packets via the Data-Plane:
Aliveness and routing protocol signaling packets across the Data-
Plane to verify reachability across the Data-Plane, using IPv4
signaling packets for IPv4 routing vs. IPv6 signaling packets for
IPv6 routing.
Assuming appropriate implementation (see Section 6.13.2 for more
details), the ACP provides reachability that is independent of the
Data-Plane. This allows the control plane and OAM plane to operate
more robustly:
* For management plane protocols, the ACP provides the functionality
of a Virtual out-of-band (VooB) channel, by providing connectivity
to all nodes regardless of their Data-Plane configuration, routing
and forwarding tables.
* For control plane protocols, the ACP allows their operation even
when the Data-Plane is temporarily faulty, or during transitional
events, such as routing changes, which may affect the control
plane at least temporarily. This is specifically important for
autonomic service agents, which could affect Data-Plane
connectivity.
The document "Using Autonomic Control Plane for Stable Connectivity
of Network OAM" [RFC8368] explains this use case for the ACP in
significantly more detail and explains how the ACP can be used in
practical network operations.
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4. Requirements (Informative)
The following requirements were identified for the design of the ACP
based on the above use-cases (Section 3). These requirements are
informative. The ACP as specified in the normative parts of this
document is meeting or exceeding these use-case requirements:
ACP1: The ACP should provide robust connectivity: As far as
possible, it should be independent of configured addressing,
configuration and routing. Requirements 2 and 3 build on this
requirement, but also have value on their own.
ACP2: The ACP must have a separate address space from the Data-
Plane. Reason: traceability, debug-ability, separation from
Data-Plane, infrastructure security (filtering based on known
address space).
ACP3: The ACP must use autonomically managed address space. Reason:
easy bootstrap and setup ("autonomic"); robustness (admin
cannot break network easily). This document uses Unique Local
Addresses (ULA) for this purpose, see [RFC4193].
ACP4: The ACP must be generic, that is it must be usable by all the
functions and protocols of the ANI. Clients of the ACP must
not be tied to a particular application or transport protocol.
ACP5: The ACP must provide security: Messages coming through the ACP
must be authenticated to be from a trusted node, and it is
very strongly > recommended that they be encrypted.
Explanation for ACP4: In a fully autonomic network (AN), newly
written ASAs could potentially all communicate exclusively via GRASP
with each other, and if that was assumed to be the only requirement
against the ACP, it would not need to provide IPv6 layer connectivity
between nodes, but only GRASP connectivity. Nevertheless, because
ACP also intends to support non-AN networks, it is crucial to support
IPv6 layer connectivity across the ACP to support any transport and
application layer protocols.
The ACP operates hop-by-hop, because this interaction can be built on
IPv6 link local addressing, which is autonomic, and has no dependency
on configuration (requirement 1). It may be necessary to have ACP
connectivity across non-ACP nodes, for example to link ACP nodes over
the general Internet. This is possible, but introduces a dependency
against stable/resilient routing over the non-ACP hops (see
Section 8.2).
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5. Overview (Informative)
When a node has an ACP certificate (see Section 6.2.1) and is enabled
to bring up the ACP (see Section 9.3.5), it will create its ACP
without any configuration as follows. For details, see Section 6 and
further sections:
1. The node creates a VRF instance, or a similar virtual context for
the ACP.
2. The node assigns its ULA IPv6 address (prefix) (see Section 6.11
which is learned from the acp-node-name (see Section 6.2.2) of
its ACP certificate (see Section 6.2.1) to an ACP loopback
interface (see Section 6.11) and connects this interface into the
ACP VRF.
3. The node establishes a list of candidate peer adjacencies and
candidate channel types to try for the adjacency. This is
automatic for all candidate link-local adjacencies, see
Section 6.4 across all native interfaces (see Section 9.3.4). If
a candidate peer is discovered via multiple interfaces, this will
result in one adjacency per interface. If the ACP node has
multiple interfaces connecting to the same subnet across which it
is also operating as an L2 switch in the Data-Plane, it employs
methods for ACP with L2 switching, see Section 7.
4. For each entry in the candidate adjacency list, the node
negotiates a secure tunnel using the candidate channel types.
See Section 6.6.
5. The node authenticates the peer node during secure channel setup
and authorizes it to become part of the ACP according to
Section 6.2.3.
6. Unsuccessful authentication of a candidate peer results in
throttled connection retries for as long as the candidate peer is
discoverable. See Section 6.7.
7. Each successfully established secure channel is mapped into an
ACP virtual interface, which is placed into the ACP VRF. See
Section 6.13.5.2.
8. Each node runs a lightweight routing protocol, see Section 6.12,
to announce reachability of the ACP loopback address (or prefix)
across the ACP.
9. This completes the creation of the ACP with hop-by-hop secure
tunnels, auto-addressing and auto-routing. The node is now an
ACP node with a running ACP.
Note:
* None of the above operations (except the following explicit
configured ones) are reflected in the configuration of the node.
* Non-ACP NMS ("Network Management Systems") or SDN controllers have
to be explicitly configured for connection into the ACP.
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* Additional candidate peer adjacencies for ACP connections across
non-ACP Layer-3 clouds requires explicit configuration. See
Section 8.2.
The following figure illustrates the ACP.
ACP node 1 ACP node 2
................... ...................
secure . . secure . . secure
channel: +-----------+ : channel : +-----------+ : channel
..--------| ACP VRF |---------------------| ACP VRF |---------..
: / \ / \ <--routing--> / \ / \ :
: \ / \ / \ / \ / :
..--------| Loopback |---------------------| Loopback |---------..
: | interface | : : | interface | :
: +-----------+ : : +-----------+ :
: : : :
: Data-Plane :...............: Data-Plane :
: : link : :
:.................: :.................:
Figure 1: ACP VRF and secure channels
The resulting overlay network is normally based exclusively on hop-
by-hop tunnels. This is because addressing used on links is IPv6
link local addressing, which does not require any prior set-up. In
this way the ACP can be built even if there is no configuration on
the node, or if the Data-Plane has issues such as addressing or
routing problems.
6. Self-Creation of an Autonomic Control Plane (ACP) (Normative)
This section specifies the components and steps to set up an ACP.
The ACP is automatically "self-creating", which makes it
"indestructible" against most changes to the Data-Plane, including
misconfigurations of routing, addressing, NAT, firewall or any other
traffic policy filters that inadvertently or otherwise unavoidably
would also impact the management plane traffic, such as the actual
operator CLI session or controller NETCONF session through which the
configuration changes to the Data-Plane are executed.
Physical misconfiguration of wiring between ACP nodes will also not
break the ACP: As long as there is a transitive physical path between
ACP nodes, the ACP should be able to recover given that it
automatically operates across all interfaces of the ACP nodes and
automatically determines paths between them.
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Attacks against the network via incorrect routing or addressing
information for the Data-Plane will not impact the ACP. Even
impaired ACP nodes will have a significantly reduced attack surface
against malicious misconfiguration because only very limited ACP or
interface up/down configuration can affect the ACP, and pending on
their specific designs these type of attacks could also be
eliminated. See more in Section 9.3 and Section 11.
An ACP node can be a router, switch, controller, NMS host, or any
other IPv6 capable node. Initially, it MUST have its ACP
certificate, as well as an (empty) ACP Adjacency Table (described in
Section 6.3). It then can start to discover ACP neighbors and build
the ACP. This is described step by step in the following sections:
6.1. Requirements for use of Transport Layer Security (TLS)
The following requirements apply to TLS required or used by ACP
components. Applicable ACP components include ACP certificate
maintenance via EST, see Section 6.2.5, TLS connections for
Certificate Revocation List (CRL) Distribution Point (CRLDP) or
Online Certificate Status Protocol (OCSP) responder (if used, see
Section 6.2.3) and ACP GRASP (see Section 6.9.2). On ANI nodes these
requirements also apply to BRSKI.
TLS MUST comply with [RFC7525] except that TLS 1.2 ([RFC5246]) is
REQUIRED and that older versions of TLS MUST NOT be used. TLS 1.3
([RFC8446]) SHOULD be supported. The choice for TLS 1.2 as the
lowest common denominator for the ACP is based on current expected
most likely availability across the wide range of candidate ACP node
types, potentially with non-agile operating system TCP/IP stacks.
TLS MUST offer TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 and
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 and MUST NOT offer options
with less than 256-bit symmetric key strength or hash strength of
less than 384 bits. When TLS 1.3 is supported,
TLS_AES_256_GCM_SHA384 MUST be offered and
TLS_CHACHA20_POLY1305_SHA256 MAY be offered.
TLS MUST also include the "Supported Elliptic Curves" extension, it
MUST support the NIST P-256 (secp256r1(22)) and P-384 (secp384r1(24))
curves [RFC8422]. In addition, TLS 1.2 clients SHOULD send an
ec_point_format extension with a single element, "uncompressed".
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6.2. ACP Domain, Certificate and Network
The ACP relies on group security. An ACP domain is a group of nodes
that trust each other to participate in ACP operations such as
creating ACP secure channels in an autonomous peer-to-peer fashion
between ACP domain members via protocols such as IPsec. To
authenticate and authorize another ACP member node with access to the
ACP Domain, each ACP member requires keying material: An ACP node
MUST have a Local Device IDentity (LDevID) certificate, henceforth
called the ACP certificate and information about one or more Trust
Anchor (TA) as required for the ACP domain membership check
(Section 6.2.3).
Manual keying via shared secrets is not usable for an ACP domain
because it would require a single shared secret across all current
and future ACP domain members to meet the expectation of autonomous,
peer-to-peer establishment of ACP secure channels between any ACP
domain members. Such a single shared secret would be an inacceptable
security weakness. Asymmetric keying material (public keys) without
certificates does not provide the mechanisms to authenticate ACP
domain membership in an autonomous, peer-to-peer fashion for current
and future ACP domain members.
The LDevID certificate is called the ACP certificate. The TA is the
Certification Authority (CA) root certificate of the ACP domain.
The ACP does not mandate specific mechanisms by which this keying
material is provisioned into the ACP node. It only requires the
certificate to comply with Section 6.2.1, specifically to have the
acp-node-name as specified in Section 6.2.2 in its domain certificate
as well as those of candidate ACP peers. See Appendix A.2 for more
information about enrollment or provisioning options.
This document uses the term ACP in many places where the Autonomic
Networking reference documents [RFC7575] and
[I-D.ietf-anima-reference-model] use the word autonomic. This is
done because those reference documents consider (only) fully
autonomic networks and nodes, but support of ACP does not require
support for other components of autonomic networks except for relying
on GRASP and providing security and transport for GRASP. Therefore,
the word autonomic might be misleading to operators interested in
only the ACP.
[RFC7575] defines the term "Autonomic Domain" as a collection of
autonomic nodes. ACP nodes do not need to be fully autonomic, but
when they are, then the ACP domain is an autonomic domain. Likewise,
[I-D.ietf-anima-reference-model] defines the term "Domain
Certificate" as the certificate used in an autonomic domain. The ACP
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certificate is that domain certificate when ACP nodes are (fully)
autonomic nodes. Finally, this document uses the term ACP network to
refer to the network created by active ACP nodes in an ACP domain.
The ACP network itself can extend beyond ACP nodes through the
mechanisms described in Section 8.1.
6.2.1. ACP Certificates
ACP certificates MUST be [RFC5280] compliant X.509 v3 ([X.509])
certificates.
ACP nodes MUST support handling ACP certificates, TA certificates and
certificate chain certificates (henceforth just called certificates
in this section) with RSA public keys and certificates with Elliptic
Curve (ECC) public keys.
ACP nodes MUST NOT support certificates with RSA public keys of less
than 2048-bit modulus or curves with group order of less than
256-bit. They MUST support certificates with RSA public keys with
2048-bit modulus and MAY support longer RSA keys. They MUST support
certificates with ECC public keys using NIST P-256 curves and SHOULD
support P-384 and P-521 curves.
ACP nodes MUST NOT support certificates with RSA public keys whose
modulus is less than 2048 bits, or certificates whose ECC public keys
are in groups whose order is less than 256-bits. RSA signing
certificates with 2048-bit public keys MUST be supported, and such
certificates with longer public keys MAY be supported. ECDSA
certificates using the NIST P-256 curve MUST be supported, and such
certificates using the P-384 and P-521 curves SHOULD be supported.
ACP nodes MUST support RSA certificates that are signed by RSA
signatures over the SHA-256 digest of the contents, and SHOULD
additionally support SHA-384 and SHA-512 digests in such signatures.
The same requirements for digest usage in certificate signatures
apply to ECDSA certificates, and additionally, ACP nodes MUST support
ECDSA signatures on ECDSA certificates.
The ACP certificate SHOULD use an RSA key and an RSA signature when
the ACP certificate is intended to be used not only for ACP
authentication but also for other purposes. The ACP certificate MAY
use an ECC key and an ECDSA signature if the ACP certificate is only
used for ACP and ANI authentication and authorization.
Any secure channel protocols used for the ACP as specified in this
document or extensions of this document MUST therefore support
authentication (e.g. signing) starting with these type of
certificates. See [RFC8422] for more information.
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The reason for these choices are as follows: As of 2020, RSA is still
more widely used than ECC, therefore the MUST for RSA. ECC offers
equivalent security at (logarithmically) shorter key lengths (see
[RFC8422]). This can be beneficial especially in the presence of
constrained bandwidth or constrained nodes in an ACP/ANI network.
Some ACP functions such as GRASP peer-2-peer across the ACP require
end-to-end/any-to-any authentication/authorization, therefore ECC can
only reliably be used in the ACP when it MUST be supported on all ACP
nodes. RSA signatures are mandatory to be supported also for ECC
certificates because CAs themselves may not support ECC yet.
The ACP certificate SHOULD be used for any authentication between
nodes with ACP domain certificates (ACP nodes and NOC nodes) where a
required authorization condition is ACP domain membership, such as
ACP node to NOC/OAM end-to-end security and ASA to ASA end-to-end
security. Section 6.2.3 defines this "ACP domain membership check".
The uses of this check that are standardized in this document are for
the establishment of hop-by-hop ACP secure channels (Section 6.7) and
for ACP GRASP (Section 6.9.2) end-to-end via TLS.
The ACP domain membership check requires a minimum amount of elements
in a certificate as described in Section 6.2.3. The identity of a
node in the ACP is carried via the acp-node-name as defined in
Section 6.2.2.
To support ECDH directly with the key in the ACP certificate, ACP
certificates with ECC keys need to indicate to be Elliptic Curve
Diffie-Hellman capable (ECDH): If the X.509v3 keyUsage extension is
present, the keyAgreement bit must then be set. Note that this
option is not required for any of the required ciphersuites in this
document and may not be supported by all CA.
Any other fields of the ACP certificate are to be populated as
required by [RFC5280]: As long as they are compliant with [RFC5280],
any other field of an ACP certificate can be set as desired by the
operator of the ACP domain through appropriate ACP registrar/ACP CA
procedures. For example, other fields may be required for other
purposes that the ACP certificate is intended to be used for (such as
elements of a SubjectName).
For further certificate details, ACP certificates may follow the
recommendations from [CABFORUM].
For diagnostic and other operational purposes, it is beneficial to
copy the device identifying fields of the node's IDevID certificate
into the ACP certificate, such as the [X.520], section 6.2.9
"serialNumber" attribute in the subject field distinguished name
encoding. Note that this is not the certificate serial number. See
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also [I-D.ietf-anima-bootstrapping-keyinfra] section 2.3.1. This can
be done for example if it would be acceptable for the device's
"serialNumber" to be signaled via the Link Layer Discovery Protocol
(LLDP, [LLDP]) because like LLDP signaled information, the ACP
certificate information can be retrieved by neighboring nodes without
further authentication and be used either for beneficial diagnostics
or for malicious attacks. Retrieval of the ACP certificate is
possible via a (failing) attempt to set up an ACP secure channel, and
the "serialNumber" usually contains device type information that may
help to faster determine working exploits/attacks against the device.
Note that there is no intention to constrain authorization within the
ACP or autonomic networks using the ACP to just the ACP domain
membership check as defined in this document. It can be extended or
modified with additional requirements. Such future authorizations
can use and require additional elements in certificates or policies
or even additional certificates. See the additional check against
the id-kp-cmcRA [RFC6402] extended key usage attribute
(Section 6.2.5) and for possible future extensions, see
Appendix A.9.5.
6.2.2. ACP Certificate AcpNodeName
acp-node-name = local-part "@" acp-domain-name
local-part = [ acp-address ] [ "+" rsub extensions ]
acp-address = 32HEXDIG | "0" ; HEXDIG as of RFC5234 section B.1
rsub = [ <subdomain> ] ; <subdomain> as of RFC1034, section 3.5
acp-domain-name = ; <domain> ; as of RFC 1034, section 3.5
extensions = *( "+" extension )
extension = 1*etext ; future standard definition.
etext = ALPHA / DIGIT / ; Printable US-ASCII
"!" / "#" / "$" / "%" / "&" / "'" /
"*" / "-" / "/" / "=" / "?" / "^" /
"_" / "`" / "{" / "|" / "}" / "~"
routing-subdomain = [ rsub "." ] acp-domain-name
Example:
given an ACP address of fd89:b714:f3db:0:200:0:6400:0000
and an ACP domain-name of acp.example.com
and an rsub extenstion of area51.research
then this results in:
acp-node-name = fd89b714f3db00000200000064000000
+area51.research@acp.example.com
acp-domain-name = acp.example.com
routing-subdomain = area51.research.acp.example.com
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Figure 2: ACP Node Name ABNF
acp-node-name in above Figure 2 is the ABNF ([RFC5234]) definition of
the ACP Node Name. An ACP certificate MUST carry this information.
It MUST be encoded as a subjectAltName / otherName / AcpNodeName as
described in Section 6.2.2.1.
Nodes complying with this specification MUST be able to receive their
ACP address through the domain certificate, in which case their own
ACP certificate MUST have a 32HEXDIG acp-address field. Acp-address
is case insensitive because ABNF HEXDIG is. It is recommended to
encode acp-address with lower case letters. Nodes complying with
this specification MUST also be able to authenticate nodes as ACP
domain members or ACP secure channel peers when they have a 0-value
acp-address field and as ACP domain members (but not as ACP secure
channel peers) when the acp-address field is omitted from their
AcpNodeName. See Section 6.2.3.
acp-domain-name is used to indicate the ACP Domain across which ACP
nodes authenticate and authorize each other, for example to build ACP
secure channels to each other, see Section 6.2.3. acp-domain-name
SHOULD be the FQDN of an Internet domain owned by the network
administration of the ACP and ideally reserved to only be used for
the ACP. In this specification it serves to be a name for the ACP
that ideally is globally unique. When acp-domain-name is a globally
unique name, collision of ACP addresses across different ACP domains
can only happen due to ULA hash collisions (see Section 6.11.2).
Using different acp-domain-names, operators can distinguish multiple
ACP even when using the same TA.
To keep the encoding simple, there is no consideration for
internationalized acp-domain-names. The acp-node-name is not
intended for end user consumption. There is no protection against an
operator to pick any domain name for an ACP whether or not the
operator can claim to own the domain name. Instead, the domain name
only serves as a hash seed for the ULA and for diagnostics to the
operator. Therefore, any operator owning only an internationalized
domain name should be able to pick an equivalently unique 7-bit ASCII
acp-domain-name string representing the internationalized domain
name.
"routing-subdomain" is a string that can be constructed from the acp-
node-name, and it is used in the hash-creation of the ULA (see
below). The presence of the "rsub" component allows a single ACP
domain to employ multiple /48 ULA prefixes. See Appendix A.6 for
example use-cases.
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The optional "extensions" field is used for future standardized
extensions to this specification. It MUST be ignored if present and
not understood.
The following points explain and justify the encoding choices
described:
1. Formatting notes:
1.1 "rsub" needs to be in the "local-part": If the format just
had routing-subdomain as the domain part of the acp-node-
name, rsub and acp-domain-name could not be separated from
each other to determine in the ACP domain membership check
which part is the acp-domain-name and which is solely for
creating a different ULA prefix.
1.2 If both "acp-address" and "rsub" are omitted from
AcpNodeName, the "local-part" will have the format
"++extension(s)". The two plus characters are necessary so
the node can unambiguously parse that both "acp-address" and
"rsub" are omitted.
2. The encoding of the ACP domain name and ACP address as described
in this section is used for the following reasons:
2.1 The acp-node-name is the identifier of a node's ACP. It
includes the necessary components to identify a node's ACP
both from within the ACP as well as from the outside of the
ACP.
2.2 For manual and/or automated diagnostics and backend
management of devices and ACPs, it is necessary to have an
easily human readable and software parsed standard, single
string representation of the information in the acp-node-
name. For example, inventory or other backend systems can
always identify an entity by one unique string field but not
by a combination of multiple fields, which would be
necessary if there was no single string representation.
2.3 If the encoding was not that of such a string, it would be
necessary to define a second standard encoding to provide
this format (standard string encoding) for operator
consumption.
2.4 Addresses of the form <local>@<domain> have become the
preferred format for identifiers of entities in many
systems, including the majority of user identification in
web or mobile applications such as multi-domain single-sign-
on systems.
3. Compatibilities:
3.1 It should be possible to use the ACP certificate as an
LDevID certificate on the system for other uses beside the
ACP. Therefore, the information element required for the
ACP should be encoded so that it minimizes the possibility
of creating incompatibilities with such other uses. The
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attributes of the subject field for example are often used
in non-ACP applications and should therefore not be occupied
by new ACP values.
3.2 The element should not require additional ASN.1 en/decoding,
because libraries to access certificate information
especially for embedded devices may not support extended
ASN.1 decoding beyond predefined, mandatory fields.
subjectAltName / otherName is already used with a single
string parameter for several otherNames (see [RFC3920],
[RFC7585], [RFC4985], [RFC8398]).
3.3 The element required for the ACP should minimize the risk of
being misinterpreted by other uses of the LDevID
certificate. It also must not be misinterpreted to actually
be an email address, hence the use of the otherName /
rfc822Name option in the certificate would be inappropriate.
See section 4.2.1.6 of [RFC5280] for details on the subjectAltName
field.
6.2.2.1. AcpNodeName ASN.1 Module
The following ASN.1 module normatively specifies the AcpNodeName
structure. This specification uses the ASN.1 definitions from
[RFC5912] with the 2002 ASN.1 notation used in that document.
[RFC5912] updates normative documents using older ASN.1 notation.
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ANIMA-ACP-2020
{ iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-anima-acpnodename-2020(IANA1) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
OTHER-NAME
FROM PKIX1Implicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-implicit-02(59) }
id-pkix
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
AcpNodeNameOtherNames OTHER-NAME ::= { on-AcpNodeName, ... }
on-AcpNodeName OTHER-NAME ::= {
AcpNodeName IDENTIFIED BY id-on-AcpNodeName
}
id-on-AcpNodeName OBJECT IDENTIFIER ::= { id-on IANA2 }
AcpNodeName ::= IA5String (SIZE (1..MAX))
-- AcpNodeName as specified in this document carries the
-- acp-node-name as specified in the ABNF in Section 6.1.2
END
Figure 3
6.2.3. ACP domain membership check
The following points constitute the ACP domain membership check of a
candidate peer via its certificate:
1: The peer has proved ownership of the private key associated with
the certificate's public key. This check is performed by the
security association protocol used, for example [RFC7296], section
2.15.
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2: The peer's certificate passes certificate path validation as
defined in [RFC5280], section 6 against one of the TA associated
with the ACP node's ACP certificate (see Section 6.2.4 below).
This includes verification of the validity (lifetime) of the
certificates in the path.
3: If the peer's certificate indicates a Certificate Revocation List
(CRL) Distribution Point (CRLDP) ([RFC5280], section 4.2.1.13) or
Online Certificate Status Protocol (OCSP) responder ([RFC5280],
section 4.2.2.1), then the peer's certificate MUST be valid
according to those mechanisms when they are available: An OCSP
check for the peer's certificate across the ACP must succeed or
the peer certificate must not be listed in the CRL retrieved from
the CRLDP. These mechanisms are not available when the ACP node
has no ACP or non-ACP connectivity to retrieve a current CRL or
access an OCSP responder and the security association protocol
itself has also no way to communicate CRL or OCSP check.
Retries to learn revocation via OCSP/CRL SHOULD be made using the
same backoff as described in Section 6.7. If and when the ACP
node then learns that an ACP peer's certificate is invalid for
which rule 3 had to be skipped during ACP secure channel
establishment, then the ACP secure channel to that peer MUST be
closed even if this peer is the only connectivity to access CRL/
OCSP. This applies (of course) to all ACP secure channels to this
peer if there are multiple. The ACP secure channel connection
MUST be retried periodically to support the case that the neighbor
acquires a new, valid certificate.
4: The peer's certificate has a syntactically valid acp-node-name
field and the acp-domain-name in that peer's acp-node-name is the
same as in this ACP node's certificate (lowercase normalized).
When checking a candidate peer's certificate for the purpose of
establishing an ACP secure channel, one additional check is
performed:
5: The acp-address field of the candidate peer certificate's
AcpNodeName is not omitted but either 32HEXDIG or 0, according to
Figure 2.
Technically, ACP secure channels can only be built with nodes that
have an acp-address. Rule 5 ensures that this is taken into account
during ACP domain membership check.
Nodes with an omitted acp-address field can only use their ACP domain
certificate for non-ACP-secure channel authentication purposes. This
includes for example NMS type nodes permitted to communicate into the
ACP via ACP connect (Section 8.1)
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The special value 0 in an ACP certificates acp-address field is used
for nodes that can and should determine their ACP address through
other mechanisms than learning it through the acp-address field in
their ACP certificate. These ACP nodes are permitted to establish
ACP secure channels. Mechanisms for those nodes to determine their
ACP address are outside the scope of this specification, but this
option is defined here so that any ACP nodes can build ACP secure
channels to them according to Rule 5.
The optional rsub field of the AcpNodeName is not relevant to the ACP
domain membership check because it only serves to structure routing
and addressing within an ACP but not to segment mutual
authentication/authorization (hence the name "routing subdomain").
In summary:
* Steps 1...4 constitute standard certificate validity verification
and private key authentication as defined by [RFC5280] and
security association protocols (such as Internet Key Exchange
Protocol version 2 IKEv2 [RFC7296] when leveraging certificates.
* Steps 1...4 do not include verification of any pre-existing form
of non-public-key-only based identity elements of a certificate
such as a web servers domain name prefix often encoded in
certificate common name. Step 5 is an equivalent step for the
AcpNodeName.
* Step 4 constitutes standard CRL/OCSP checks refined for the case
of missing connectivity and limited functionality security
association protocols.
* Steps 1...4 authorize to build any secure connection between
members of the same ACP domain except for ACP secure channels.
* Step 5 is the additional verification of the presence of an ACP
address as necessary for ACP secure channels.
* Steps 1...5 therefore authorize to build an ACP secure channel.
For brevity, the remainder of this document refers to this process
only as authentication instead of as authentication and
authorization.
[RFC-Editor: Please remove the following paragraph].
Note that the ACP domain membership check does not verify the network
layer address of the security association. See [ACPDRAFT],
Appendix B.2 for explanations.
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6.2.3.1. Realtime clock and Time Validation
An ACP node with a realtime clock in which it has confidence, MUST
check the time stamps when performing ACP domain membership check
such as the certificate validity period in step 1. and the respective
times in step 4 for revocation information (e.g., signingTimes in CMS
signatures).
An ACP node without such a realtime clock MAY ignore those time stamp
validation steps if it does not know the current time. Such an ACP
node SHOULD obtain the current time in a secured fashion, such as via
a Network Time Protocol signaled through the ACP. It then ignores
time stamp validation only until the current time is known. In the
absence of implementing a secured mechanism, such an ACP node MAY use
a current time learned in an insecure fashion in the ACP domain
membership check.
Current time MAY for example be learned unsecured via NTP ([RFC5905])
over the same link-local IPv6 addresses used for the ACP from
neighboring ACP nodes. ACP nodes that do provide NTP insecure over
their link-local addresses SHOULD primarily run NTP across the ACP
and provide NTP time across the ACP only when they have a trusted
time source. Details for such NTP procedures are beyond the scope of
this specification.
Beside ACP domain membership check, the ACP itself has no dependency
against knowledge of the current time, but protocols and services
using the ACP will likely have the need to know the current time.
For example, event logging.
6.2.4. Trust Anchors (TA)
ACP nodes need TA information according to [RFC5280], section 6.1.1
(d), typically in the form of one or more certificate of the TA to
perform certificate path validation as required by Section 6.2.3,
rule 2. TA information MUST be provisioned to an ACP node (together
with its ACP domain certificate) by an ACP Registrar during initial
enrollment of a candidate ACP node. ACP nodes MUST also support
renewal of TA information via EST as described below in
Section 6.2.5.
The required information about a TA can consist of not only a single,
but multiple certificates as required for dealing with CA certificate
renewals as explained in Section 4.4 of CMP ([RFC4210]).
A certificate path is a chain of certificates starting at the ACP
certificate (leaf/end-entity) followed by zero or more intermediate
CA certificates and ending with the TA information, which are
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typically one or two the self-signed certificates of the TA. The CA
that signs the ACP certificate is called the assigning CA. If there
are no intermediate CA, then the assigning CA is the TA. Certificate
path validation authenticates that the ACP certificate is permitted
by a TA associated with the ACP, directly or indirectly via one or
more intermediate CA.
Note that different ACP nodes may have different intermediate CA in
their certificate path and even different TA. The set of TA for an
ACP domain must be consistent across all ACP members so that any ACP
node can authenticate any other ACP node. The protocols through
which ACP domain membership check rules 1-3 are performed need to
support the exchange not only of the ACP nodes certificates, but also
exchange of the intermedia TA.
ACP nodes MUST support for the ACP domain membership check the
certificate path validation with 0 or 1 intermediate CA. They SHOULD
support 2 intermediate CA and two TA (to permit migration to from one
TA to another TA).
Certificates for an ACP MUST only be given to nodes that are allowed
to be members of that ACP. When the signing CA relies on an ACP
Registrar, the CA MUST only sign certificates with acp-node-name
through trusted ACP Registrars. In this setup, any existing CA,
unaware of the formatting of acp-node-name, can be used.
These requirements can be achieved by using a TA private to the owner
of the ACP domain or potentially through appropriate contractual
agreements between the involved parties (Registrar and CA). Using
public CA is out of scope of this document. [RFC-Editor: please
remove the following sentence]. See [ACPDRAFT], Appendix B.3 for
further considerations.
A single owner can operate multiple independent ACP domains from the
same set of TA. Registrars must then know which ACP a node needs to
be enrolled into.
6.2.5. Certificate and Trust Anchor Maintenance
ACP nodes MUST support renewal of their Certificate and TA
information via EST and MAY support other mechanisms. See
Section 6.1 for TLS requirements. An ACP network MUST have at least
one ACP node supporting EST server functionality across the ACP so
that EST renewal is useable.
ACP nodes SHOULD be able to remember the IPv6 locator parameters of
the O_IPv6_LOCATOR in GRASP of the EST server from which they last
renewed their ACP certificate. They SHOULD provide the ability for
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these EST server parameters to also be set by the ACP Registrar (see
Section 6.11.7) that initially enrolled the ACP device with its ACP
certificate. When BRSKI (see
[I-D.ietf-anima-bootstrapping-keyinfra]) is used, the IPv6 locator of
the BRSKI registrar from the BRSKI TLS connection SHOULD be
remembered and used for the next renewal via EST if that registrar
also announces itself as an EST server via GRASP (see next section)
on its ACP address.
The EST server MUST present a certificate that is passing ACP domain
membership check in its TLS connection setup (Section 6.2.3, rules
1...4, not rule 5 as this is not for an ACP secure channel setup).
The EST server certificate MUST also contain the id-kp-cmcRA
[RFC6402] extended key usage attribute and the EST client MUST check
its presence.
The additional check against the id-kp-cmcRA extended key usage
extension field ensures that clients do not fall prey to an illicit
EST server. While such illicit EST servers should not be able to
support certificate signing requests (as they are not able to elicit
a signing response from a valid CA), such an illicit EST server would
be able to provide faked CA certificates to EST clients that need to
renew their CA certificates when they expire.
Note that EST servers supporting multiple ACP domains will need to
have for each of these ACP domains a separate certificate and respond
on a different transport address (IPv6 address and/or TCP port), but
this is easily automated on the EST server as long as the CA does not
restrict registrars to request certificates with the id-kp-cmcRA
extended usage extension for themselves.
6.2.5.1. GRASP objective for EST server
ACP nodes that are EST servers MUST announce their service via GRASP
in the ACP through M_FLOOD messages. See [I-D.ietf-anima-grasp],
section 2.8.11 for the definition of this message type:
Example:
[M_FLOOD, 12340815, h'fd89b714f3db0000200000064000001', 210000,
[["SRV.est", 4, 255 ],
[O_IPv6_LOCATOR,
h'fd89b714f3db0000200000064000001', IPPROTO_TCP, 443]]
]
Figure 4: GRASP SRV.est example
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The formal definition of the objective in Concise data definition
language (CDDL) (see [RFC8610]) is as follows:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
; see example above and explanation
; below for initiator and ttl
objective = ["SRV.est", objective-flags, loop-count,
objective-value]
objective-flags = sync-only ; as in GRASP spec
sync-only = 4 ; M_FLOOD only requires synchronization
loop-count = 255 ; recommended as there is no mechanism
; to discover network diameter.
objective-value = any ; reserved for future extensions
Figure 5: GRASP SRV.est definition
The objective name "SRV.est" indicates that the objective is an
[RFC7030] compliant EST server because "est" is an [RFC6335]
registered service name for [RFC7030]. Objective-value MUST be
ignored if present. Backward compatible extensions to [RFC7030] MAY
be indicated through objective-value. Non [RFC7030] compatible
certificate renewal options MUST use a different objective-name.
Non-recognized objective-values (or parts thereof if it is a
structure partially understood) MUST be ignored.
The M_FLOOD message MUST be sent periodically. The default SHOULD be
60 seconds; the value SHOULD be operator configurable but SHOULD be
not smaller than 60 seconds. The frequency of sending MUST be such
that the aggregate amount of periodic M_FLOODs from all flooding
sources cause only negligible traffic across the ACP. The time-to-
live (ttl) parameter SHOULD be 3.5 times the period so that up to
three consecutive messages can be dropped before considering an
announcement expired. In the example above, the ttl is 210000 msec,
3.5 times 60 seconds. When a service announcer using these
parameters unexpectedly dies immediately after sending the M_FLOOD,
receivers would consider it expired 210 seconds later. When a
receiver tries to connect to this dead service before this timeout,
it will experience a failing connection and use that as an indication
that the service instance is dead and select another instance of the
same service instead (from another GRASP announcement).
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The "SRV.est" objective(s) SHOULD only be announced when the ACP node
knows that it can successfully communicate with a CA to perform the
EST renewal/rekeying operations for the ACP domain. See also
Section 11.
6.2.5.2. Renewal
When performing renewal, the node SHOULD attempt to connect to the
remembered EST server. If that fails, it SHOULD attempt to connect
to an EST server learned via GRASP. The server with which
certificate renewal succeeds SHOULD be remembered for the next
renewal.
Remembering the last renewal server and preferring it provides
stickiness which can help diagnostics. It also provides some
protection against off-path compromised ACP members announcing bogus
information into GRASP.
Renewal of certificates SHOULD start after less than 50% of the
domain certificate lifetime so that network operations has ample time
to investigate and resolve any problems that causes a node to not
renew its domain certificate in time - and to allow prolonged periods
of running parts of a network disconnected from any CA.
6.2.5.3. Certificate Revocation Lists (CRLs)
The ACP node SHOULD support revocation through CRL(s) via HTTP from
one or more CRL Distribution Points (CRLDP). The CRLDP(s) MUST be
indicated in the Domain Certificate when used. If the CRLDP URL uses
an IPv6 address (ULA address when using the addressing rules
specified in this document), the ACP node will connect to the CRLDP
via the ACP. If the CRLDP uses a domain name, the ACP node will
connect to the CRLDP via the Data-Plane.
It is common to use domain names for CRLDP(s), but there is no
requirement for the ACP to support DNS. Any DNS lookup in the Data-
Plane is not only a possible security issue, but it would also not
indicate whether the resolved address is meant to be reachable across
the ACP. Therefore, the use of an IPv6 address versus the use of a
DNS name doubles as an indicator whether or not to reach the CRLDP
via the ACP.
A CRLDP can be reachable across the ACP either by running it on a
node with ACP or by connecting its node via an ACP connect interface
(see Section 8.1).
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When using a private PKI for ACP certificates, the CRL may be need-
to-know, for example to prohibit insight into the operational
practices of the domain by tracking the growth of the CRL. In this
case, HTTPS may be chosen to provide confidentiality, especially when
making the CRL available via the Data-Plane. Authentication and
authorization SHOULD use ACP certificates and ACP domain membership
check. The CRLDP MAY omit the CRL verification during authentication
of the peer to permit retrieval of the CRL by an ACP node with
revoked ACP certificate. This can allow for that (ex) ACP node to
quickly discover its ACP certificate revocation. This may violate
the desired need-to-know requirement though. ACP nodes MAY support
CRLDP operations via HTTPS.
6.2.5.4. Lifetimes
Certificate lifetime may be set to shorter lifetimes than customary
(1 year) because certificate renewal is fully automated via ACP and
EST. The primary limiting factor for shorter certificate lifetimes
is load on the EST server(s) and CA. It is therefore recommended
that ACP certificates are managed via a CA chain where the assigning
CA has enough performance to manage short lived certificates. See
also Section 9.2.4 for discussion about an example setup achieving
this. See also [I-D.ietf-acme-star].
When certificate lifetimes are sufficiently short, such as few hours,
certificate revocation may not be necessary, allowing to simplify the
overall certificate maintenance infrastructure.
See Appendix A.2 for further optimizations of certificate maintenance
when BRSKI can be used ("Bootstrapping Remote Secure Key
Infrastructures", see [I-D.ietf-anima-bootstrapping-keyinfra]).
6.2.5.5. Re-enrollment
An ACP node may determine that its ACP certificate has expired, for
example because the ACP node was powered down or disconnected longer
than its certificate lifetime. In this case, the ACP node SHOULD
convert to a role of a re-enrolling candidate ACP node.
In this role, the node does maintain the TA and certificate chain
associated with its ACP certificate exclusively for the purpose of
re-enrollment, and attempts (or waits) to get re-enrolled with a new
ACP certificate. The details depend on the mechanisms/protocols used
by the ACP Registrars.
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Please refer to Section 6.11.7 and
[I-D.ietf-anima-bootstrapping-keyinfra] for explanations about ACP
Registrars and vouchers as used in the following text. When ACP is
intended to be used without BRSKI, the details about BRSKI and
vouchers in the following text can be skipped.
When BRSKI is used (i.e.: on ACP nodes that are ANI nodes), the re-
enrolling candidate ACP node would attempt to enroll like a candidate
ACP node (BRSKI pledge), but instead of using the ACP nodes IDevID
certificate, it SHOULD first attempt to use its ACP domain
certificate in the BRSKI TLS authentication. The BRSKI registrar MAY
honor this certificate beyond its expiration date purely for the
purpose of re-enrollment. Using the ACP node's domain certificate
allows the BRSKI registrar to learn that node's acp-node-name, so
that the BRSKI registrar can re-assign the same ACP address
information to the ACP node in the new ACP certificate.
If the BRSKI registrar denies the use of the old ACP certificate, the
re-enrolling candidate ACP node MUST re-attempt re-enrollment using
its IDevID certificate as defined in BRSKI during the TLS connection
setup.
Both when the BRSKI connection is attempted with the old ACP
certificate or the IDevID certificate, the re-enrolling candidate ACP
node SHOULD authenticate the BRSKI registrar during TLS connection
setup based on its existing TA certificate chain information
associated with its old ACP certificate. The re-enrolling candidate
ACP node SHOULD only fall back to requesting a voucher from the BRSKI
registrar when this authentication fails during TLS connection setup.
As a countermeasure against attacks that attempt to force the ACP
node to forget its prior (expired) certificate and TA, the ACP node
should alternate between attempting to re-enroll using its old keying
material and attempting to re-enroll with its IDevID and requesting a
voucher.
When other mechanisms than BRSKI are used for ACP certificate
enrollment, the principles of the re-enrolling candidate ACP node are
the same. The re-enrolling candidate ACP node attempts to
authenticate any ACP Registrar peers during re-enrollment protocol/
mechanisms via its existing certificate chain/TA information and
provides its existing ACP certificate and other identification (such
as the IDevID certificate) as necessary to the registrar.
Maintaining existing TA information is especially important when
enrollment mechanisms are used that unlike BRSKI do not leverage a
mechanism (such as the voucher in BRSKI) to authenticate the ACP
registrar and where therefore the injection of certificate failures
could otherwise make the ACP node easily attackable remotely by
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returning the ACP node to a "duckling" state in which it accepts to
be enrolled by any network it connects to. The (expired) ACP
certificate and ACP TA SHOULD therefore be maintained and attempted
to be used as one possible credential for re-enrollment until new
keying material is acquired.
When using BRSKI or other protocol/mechanisms supporting vouchers,
maintaining existing TA information allows for re-enrollment of
expired ACP certificates to be more lightweight, especially in
environments where repeated acquisition of vouchers during the
lifetime of ACP nodes may be operationally expensive or otherwise
undesirable.
6.2.5.6. Failing Certificates
An ACP certificate is called failing in this document, if/when the
ACP node to which the certificate was issued can determine that it
was revoked (or explicitly not renewed), or in the absence of such
explicit local diagnostics, when the ACP node fails to connect to
other ACP nodes in the same ACP domain using its ACP certificate.
For connection failures to determine the ACP certificate as the
culprit, the peer should pass the domain membership check
(Section 6.2.3) and other reasons for the connection failure can be
excluded because of the connection error diagnostics.
This type of failure can happen during setup/refresh of a secure ACP
channel connections or any other use of the ACP certificate, such as
for the TLS connection to an EST server for the renewal of the ACP
domain certificate.
Example reasons for failing certificates that the ACP node can only
discover through connection failure are that the domain certificate
or any of its signing certificates could have been revoked or may
have expired, but the ACP node cannot self-diagnose this condition
directly. Revocation information or clock synchronization may only
be available across the ACP, but the ACP node cannot build ACP secure
channels because ACP peers reject the ACP node's domain certificate.
ACP nodes SHOULD support the option to determines whether its ACP
certificate is failing, and when it does, put itself into the role of
a re-enrolling candidate ACP node as explained above
(Section 6.2.5.5).
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6.3. ACP Adjacency Table
To know to which nodes to establish an ACP channel, every ACP node
maintains an adjacency table. The adjacency table contains
information about adjacent ACP nodes, at a minimum: Node-ID
(identifier of the node inside the ACP, see Section 6.11.3 and
Section 6.11.5), interface on which neighbor was discovered (by GRASP
as explained below), link-local IPv6 address of neighbor on that
interface, certificate (including acp-node-name). An ACP node MUST
maintain this adjacency table. This table is used to determine to
which neighbor an ACP connection is established.
Where the next ACP node is not directly adjacent (i.e., not on a link
connected to this node), the information in the adjacency table can
be supplemented by configuration. For example, the Node-ID and IP
address could be configured. See Section 8.2.
The adjacency table MAY contain information about the validity and
trust of the adjacent ACP node's certificate. However, subsequent
steps MUST always start with the ACP domain membership check against
the peer (see Section 6.2.3).
The adjacency table contains information about adjacent ACP nodes in
general, independently of their domain and trust status. The next
step determines to which of those ACP nodes an ACP connection should
be established.
6.4. Neighbor Discovery with DULL GRASP
[RFC-Editor: GRASP draft is in RFC editor queue, waiting for
dependencies, including ACP. Please ensure that references to I-
D.ietf-anima-grasp that include section number references (throughout
this document) will be updated in case any last-minute changes in
GRASP would make those section references change.
Discovery Unsolicited Link-Local (DULL) GRASP is a limited subset of
GRASP intended to operate across an insecure link-local scope. See
section 2.5.2 of [I-D.ietf-anima-grasp] for its formal definition.
The ACP uses one instance of DULL GRASP for every L2 interface of the
ACP node to discover link level adjacent candidate ACP neighbors.
Unless modified by policy as noted earlier (Section 5 bullet point
2.), native interfaces (e.g., physical interfaces on physical nodes)
SHOULD be initialized automatically to a state in which ACP discovery
can be performed and any native interfaces with ACP neighbors can
then be brought into the ACP even if the interface is otherwise not
configured. Reception of packets on such otherwise not configured
interfaces MUST be limited so that at first only IPv6 StateLess
Address Auto Configuration (SLAAC - [RFC4862]) and DULL GRASP work
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and then only the following ACP secure channel setup packets - but
not any other unnecessary traffic (e.g., no other link-local IPv6
transport stack responders for example).
Note that the use of the IPv6 link-local multicast address
(ALL_GRASP_NEIGHBORS) implies the need to use Multicast Listener
Discovery Version 2 (MLDv2, see [RFC3810]) to announce the desire to
receive packets for that address. Otherwise DULL GRASP could fail to
operate correctly in the presence of MLD snooping ([RFC4541])
switches that are not ACP supporting/enabled - because those switches
would stop forwarding DULL GRASP packets. Switches not supporting
MLD snooping simply need to operate as pure L2 bridges for IPv6
multicast packets for DULL GRASP to work.
ACP discovery SHOULD NOT be enabled by default on non-native
interfaces. In particular, ACP discovery MUST NOT run inside the ACP
across ACP virtual interfaces. See Section 9.3 for further, non-
normative suggestions on how to enable/disable ACP at node and
interface level. See Section 8.2.2 for more details about tunnels
(typical non-native interfaces). See Section 7 for how ACP should be
extended on devices operating (also) as L2 bridges.
Note: If an ACP node also implements BRSKI to enroll its ACP
certificate (see Appendix A.2 for a summary), then the above
considerations also apply to GRASP discovery for BRSKI. Each DULL
instance of GRASP set up for ACP is then also used for the discovery
of a bootstrap proxy via BRSKI when the node does not have a domain
certificate. Discovery of ACP neighbors happens only when the node
does have the certificate. The node therefore never needs to
discover both a bootstrap proxy and ACP neighbor at the same time.
An ACP node announces itself to potential ACP peers by use of the
"AN_ACP" objective. This is a synchronization objective intended to
be flooded on a single link using the GRASP Flood Synchronization
(M_FLOOD) message. In accordance with the design of the Flood
message, a locator consisting of a specific link-local IP address, IP
protocol number and port number will be distributed with the flooded
objective. An example of the message is informally:
[M_FLOOD, 12340815, h'fe80000000000000c0011001feef0000', 210000,
[["AN_ACP", 4, 1, "IKEv2" ],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001feef0000', IPPROTO_UDP, 15000]]
[["AN_ACP", 4, 1, "DTLS" ],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001feef0000', IPPROTO_UDP, 17000]]
]
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Figure 6: GRASP AN_ACP example
The formal CDDL definition is:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
objective = ["AN_ACP", objective-flags, loop-count,
objective-value]
objective-flags = sync-only ; as in the GRASP specification
sync-only = 4 ; M_FLOOD only requires synchronization
loop-count = 1 ; limit to link-local operation
objective-value = method-name / [ method, *extension ]
method = method-name / [ method-name, *method-param ]
method-name = "IKEv2" / "DTLS" / id
extension = any
method-param = any
id = text .regexp "[A-Za-z@_$]([-.]*[A-Za-z0-9@_$])*"
Figure 7: GRASP AN_ACP definition
The objective-flags field is set to indicate synchronization.
The loop-count is fixed at 1 since this is a link-local operation.
In the above example the RECOMMENDED period of sending of the
objective is 60 seconds. The indicated ttl of 210000 msec means that
the objective would be cached by ACP nodes even when two out of three
messages are dropped in transit.
The session-id is a random number used for loop prevention
(distinguishing a message from a prior instance of the same message).
In DULL this field is irrelevant but has to be set according to the
GRASP specification.
The originator MUST be the IPv6 link local address of the originating
ACP node on the sending interface.
The method-name in the 'objective-value' parameter is a string
indicating the protocol available at the specified or implied
locator. It is a protocol supported by the node to negotiate a
secure channel. IKEv2 as shown above is the protocol used to
negotiate an IPsec secure channel.
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Method-params allows to carry method specific parameters. This
specification does not define any method-param(s) for "IKEv2" or
"DTLS". Method-params for these two methods that are not understood
by an ACP node MUST be ignored by it.
extension(s) allows to define method independent parameters. This
specification does not define any extensions. Extensions not
understood by an ACP node MUST be ignored by it.
The locator-option is optional and only required when the secure
channel protocol is not offered at a well-defined port number, or if
there is no well-defined port number.
IKEv2 is the actual protocol used to negotiate an Internet Protocol
security architecture (IPsec) connection. GRASP therefore indicates
"IKEv2" and not "IPsec". If "IPsec" was used, this too could mean
use of the obsolete older version IKE (v1) ([RFC2409]). IKEv2 has an
IANA assigned port number 500, but in the above example, the
candidate ACP neighbor is offering ACP secure channel negotiation via
IKEv2 on port 15000 (purely to show through the example that GRASP
allows to indicate the port number and it does not have to be the
IANA assigned one).
There is no default UDP port for DTLS, it is always locally assigned
by the node. For further details about the "DTLS" secure channel
protocol, see Section 6.8.4.
If a locator is included, it MUST be an O_IPv6_LOCATOR, and the IPv6
address MUST be the same as the initiator address (these are DULL
requirements to minimize third party DoS attacks).
The secure channel methods defined in this document use the
objective-values of "IKEv2" and "DTLS". There is no distinction
between IKEv2 native and GRE-IKEv2 because this is purely negotiated
via IKEv2.
A node that supports more than one secure channel protocol method
needs to flood multiple versions of the "AN_ACP" objective so that
each method can be accompanied by its own locator-option. This can
use a single GRASP M_FLOOD message as shown in Figure 6.
The use of DULL GRASP primarily serves to discover the link-local
IPv6 address of candidate ACP peers on subnets. The signaling of the
supported secure channel option is primarily for diagnostic purposes,
but it is also necessary for discovery when the protocol has no well-
known transport address, such as in the case of DTLS. [RFC-Editor:
Please remove the following sentence]. See [ACPDRAFT], Appendix B.4.
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Note that a node serving both as an ACP node and BRSKI Join Proxy may
choose to distribute the "AN_ACP" objective and the respective BRSKI
in the same M_FLOOD message, since GRASP allows multiple objectives
in one message. This may be impractical though if ACP and BRSKI
operations are implemented via separate software modules / ASAs.
The result of the discovery is the IPv6 link-local address of the
neighbor as well as its supported secure channel protocols (and non-
standard port they are running on). It is stored in the ACP
Adjacency Table (see Section 6.3), which then drives the further
building of the ACP to that neighbor.
Note that the DULL GRASP objective described intentionally does not
include the ACP node's ACP certificate even though this would be
useful for diagnostics and to simplify the security exchange in ACP
secure channel security association protocols (see Section 6.8). The
reason is that DULL GRASP messages are periodically multicasted
across IPv6 subnets and full certificates could easily lead to
fragmented IPv6 DULL GRASP multicast packets due to the size of a
certificate. This would be highly undesirable.
6.5. Candidate ACP Neighbor Selection
An ACP node determines to which other ACP nodes in the adjacency
table it should attempt to build an ACP connection. This is based on
the information in the ACP Adjacency table.
The ACP is established exclusively between nodes in the same domain.
This includes all routing subdomains. Appendix A.6 explains how ACP
connections across multiple routing subdomains are special.
The result of the candidate ACP neighbor selection process is a list
of adjacent or configured autonomic neighbors to which an ACP channel
should be established. The next step begins that channel
establishment.
6.6. Channel Selection
To avoid attacks, initial discovery of candidate ACP peers cannot
include any non-protected negotiation. To avoid re-inventing and
validating security association mechanisms, the next step after
discovering the address of a candidate neighbor can only be to try
first to establish a security association with that neighbor using a
well-known security association method.
From the use-cases it seems clear that not all type of ACP nodes can
or need to connect directly to each other or are able to support or
prefer all possible mechanisms. For example, code space limited IoT
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devices may only support DTLS because that code exists already on
them for end-to-end security, but low-end in-ceiling L2 switches may
only want to support Media Access Control Security (MacSec, see
802.1AE ([MACSEC]) because that is also supported in their chips.
Only a flexible gateway device may need to support both of these
mechanisms and potentially more. Note that MacSec is not required by
any profiles of the ACP in this specification. Instead, MacSec is
mentioned as a likely next interesting secure channel protocol. Note
also that the security model allows and requires for any-to-any
authentication and authorization between all ACP nodes because there
is also end-to-end and not only hop-by-hop authentication for secure
channels.
To support extensible secure channel protocol selection without a
single common mandatory to implement (MTI) protocol, ACP nodes MUST
try all the ACP secure channel protocols it supports and that are
feasible because the candidate ACP neighbor also announced them via
its AN_ACP GRASP parameters (these are called the "feasible" ACP
secure channel protocols).
To ensure that the selection of the secure channel protocols always
succeeds in a predictable fashion without blocking, the following
rules apply:
* An ACP node may choose to attempt to initiate the different
feasible ACP secure channel protocols it supports according to its
local policies sequentially or in parallel, but it MUST support
acting as a responder to all of them in parallel.
* Once the first ACP secure channel protocol connection to a
specific peer IPv6 address passes peer authentication, the two
peers know each other's certificate because those ACP certificates
are used by all secure channel protocols for mutual
authentication. The peer with the higher Node-ID in the
AcpNodeName of its ACP certificate takes on the role of the
Decider towards the peer. The other peer takes on the role of the
Follower. The Decider selects which secure channel protocol to
ultimately use.
* The Follower becomes passive: it does not attempt to further
initiate ACP secure channel protocol connections with the Decider
and does not consider it to be an error when the Decider closes
secure channels. The Decider becomes the active party, continues
to attempt setting up secure channel protocols with the Follower.
This process terminates when the Decider arrives at the "best" ACP
secure channel connection option that also works with the Follower
("best" from the Deciders point of view).
* A peer with a "0" acp-address in its AcpNodeName takes on the role
of Follower when peering with a node that has a non-"0" acp-
address (note that this specification does not fully define the
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behavior of ACP secure channel negotiation for nodes with a "0"
ACP address field, it only defines interoperability with such ACP
nodes).
In a simple example, ACP peer Node 1 attempts to initiate an IPsec
via IKEv2 connection to peer Node 2. The IKEv2 authentication
succeeds. Node 1 has the lower ACP address and becomes the Follower.
Node 2 becomes the Decider. IKEv2 might not be the preferred ACP
secure channel protocol for the Decider Node 2. Node 2 would
therefore proceed to attempt secure channel setups with (in its view)
more preferred protocol options (e.g., DTLS/UDP). If any such
preferred ACP secure channel connection of the Decider succeeds, it
would close the IPsec connection. If Node 2 has no preferred
protocol option over IPsec, or no such connection attempt from Node 2
to Node 1 succeeds, Node 2 would keep the IPsec connection and use
it.
The Decider SHOULD NOT send actual payload packets across a secure
channel until it has decided to use it. The Follower MAY delay
linking the ACP secure channel into the ACP virtual interface until
it sees the first payload packet from the Decider up to a maximum of
5 seconds to avoid unnecessarily linking a secure channel that will
be terminated as undesired by the Decider shortly afterwards.
The following sequence of steps show this example in more detail.
Each step is tagged with [<step#>{:<connection>}]. The connection is
included to more easily distinguish which of the two competing
connections the step belongs to, one initiated by Node 1, one
initiated by Node 2.
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[1] Node 1 sends GRASP AN_ACP message to announce itself
[2] Node 2 sends GRASP AN_ACP message to announce itself
[3] Node 2 receives [1] from Node 1
[4:C1] Because of [3], Node 2 starts as initiator on its
preferred secure channel protocol towards Node 1.
Connection C1.
[5] Node 1 receives [2] from Node 2
[6:C2] Because of [5], Node 1 starts as initiator on its
preferred secure channel protocol towards Node 2.
Connection C2.
[7:C1] Node1 and Node2 have authenticated each others
certificate on connection C1 as valid ACP peers.
[8:C1] Node 1 certificate has lower ACP Node-ID than Node2, therefore
Node 1 considers itself the Follower and Node 2 the Decider
on connection C1. Connection setup C1 is completed.
[9] Node 1 refrains from attempting any further secure channel
connections to Node 2 (the Decider) as learned from [2]
because it knows from [8:C1] that it is the Follower
relative to Node 1.
[10:C2] Node1 and Node2 have authenticated each others
certificate on connection C2 (like [7:C1]).
[11:C2] Node 1 certificate has lower ACP Node-ID than Node2,
therefore Node 1 considers itself the Follower and Node 2 the
Decider on connection C2, but they also identify that C2 is
to the same mutual peer as their C1, so this has no further
impact: the roles Decider and Follower where already assigned
between these two peers by [8:C1].
[12:C2] Node 2 (the Decider) closes C1. Node 1 is fine with this,
because of its role as the Follower (from [8:C1]).
[13] Node 2 (the Decider) and Node 1 (the Follower) start data
transfer across C2, which makes it become a secure channel
for the ACP.
Figure 8: Secure Channel sequence of steps
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All this negotiation is in the context of an "L2 interface". The
Decider and Follower will build ACP connections to each other on
every "L2 interface" that they both connect to. An autonomic node
MUST NOT assume that neighbors with the same L2 or link-local IPv6
addresses on different L2 interfaces are the same node. This can
only be determined after examining the certificate after a successful
security association attempt.
The Decider SHOULD NOT suppress attempting a particular ACP secure
channel protocol connection on one L2 interface because this type of
ACP secure channel connection has failed to the peer with the same
ACP certificate on another L2 interface: Not only the supported ACP
secure channel protocol options may be different on the same ACP peer
across different L2 interfaces, but also error conditions may cause
inconsistent failures across different L2 interfaces. Avoiding such
connection attempt optimizations can therefore help to increase
robustness in the case of errors.
6.7. Candidate ACP Neighbor verification
Independent of the security association protocol chosen, candidate
ACP neighbors need to be authenticated based on their domain
certificate. This implies that any secure channel protocol MUST
support certificate based authentication that can support the ACP
domain membership check as defined in Section 6.2.3. If it fails,
the connection attempt is aborted and an error logged. Attempts to
reconnect MUST be throttled. The RECOMMENDED default is exponential
base 2 backoff with an initial retransmission time (IRT) of 10
seconds and a maximum retransmission time (MRT) of 640 seconds.
Failure to authenticate an ACP neighbor when acting in the role of a
responder of the security authentication protocol MUST NOT impact the
attempts of the ACP node to attempt establishing a connection as an
initiator. Only failed connection attempts as an initiator must
cause throttling. This rule is meant to increase resilience of
secure channel creation. Section 6.6 shows how simultaneous mutual
secure channel setup collisions are resolved.
6.8. Security Association (Secure Channel) protocols
This section describes how ACP nodes establish secured data
connections to automatically discovered or configured peers in the
ACP. Section 6.4 above described how IPv6 subnet adjacent peers are
discovered automatically. Section 8.2 describes how non IPv6 subnet
adjacent peers can be configured.
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Section 6.13.5.2 describes how secure channels are mapped to virtual
IPv6 subnet interfaces in the ACP. The simple case is to map every
ACP secure channel into a separate ACP point-to-point virtual
interface Section 6.13.5.2.1. When a single subnet has multiple ACP
peers this results in multiple ACP point-to-point virtual interfaces
across that underlying multi-party IPv6 subnet. This can be
optimized with ACP multi-access virtual interfaces
(Section 6.13.5.2.2) but the benefits of that optimization may not
justify the complexity of that option.
6.8.1. General considerations
Due to Channel Selection (Section 6.6), ACP can support an evolving
set of security association protocols and does not require support
for a single network wide MTI. ACP nodes only need to implement
those protocols required to interoperate with their candidate peers,
not with potentially any node in the ACP domain. See Section 6.8.5
for an example of this.
The degree of security required on every hop of an ACP network needs
to be consistent across the network so that there is no designated
"weakest link" because it is that "weakest link" that would otherwise
become the designated point of attack. When the secure channel
protection on one link is compromised, it can be used to send/receive
packets across the whole ACP network. Therefore, even though the
security association protocols can be different, their minimum degree
of security should be comparable.
Secure channel protocols do not need to always support arbitrary L3
connectivity between peers, but can leverage the fact that the
standard use case for ACP secure channels is an L2 adjacency. Hence,
L2 dependent mechanisms could be adopted for use as secure channel
association protocols:
L2 mechanisms such as strong encrypted radio technologies or [MACSEC]
may offer equivalent encryption and the ACP security association
protocol may only be required to authenticate ACP domain membership
of a peer and/or derive a key for the L2 mechanism. Mechanisms to
auto-discover and associate ACP peers leveraging such underlying L2
security are possible and desirable to avoid duplication of
encryption, but none are specified in this document.
Strong physical security of a link may stand in where cryptographic
security is infeasible. As there is no secure mechanism to
automatically discover strong physical security solely between two
peers, it can only be used with explicit configuration and that
configuration too could become an attack vector. This document
therefore only specifies with ACP connect (Section 8.1) one
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explicitly configured mechanism without any secure channel
association protocol - for the case where both the link and the nodes
attached to it have strong physical security.
6.8.2. Common requirements
The authentication of peers in any security association protocol MUST
use the ACP certificate according to Section 6.2.3. Because auto-
discovery of candidate ACP neighbors via GRASP (see Section 6.4) as
specified in this document does not communicate the neighbors ACP
certificate, and ACP nodes may not (yet) have any other network
connectivity to retrieve certificates, any security association
protocol MUST use a mechanism to communicate the certificate directly
instead of relying on a referential mechanism such as communicating
only a hash and/or URL for the certificate.
A security association protocol MUST use Forward Secrecy (whether
inherently or as part of a profile of the security association
protocol).
Because the ACP payload of legacy protocol payloads inside the ACP
and hop-by-hop ACP flooded GRASP information is unencrypted, the ACP
secure channel protocol requires confidentiality. Symmetric
encryption for the transmission of secure channel data MUST use
encryption schemes considered to be security wise equal to or better
than 256-bit key strength, such as AES256. There MUST NOT be support
for NULL encryption.
Security association protocols typically only signal the End Entity
certificate (e.g. the ACP certificate) and any possible intermediate
CA certificates for successful mutual authentication. The TA has to
be mutually known and trusted and therefore its certificate does not
need to be signaled for successful mutual authentication.
Nevertheless, for use with ACP secure channel setup, there SHOULD be
the option to include the TA certificate in the signaling to aid
troubleshooting, see Section 9.1.1.
Signaling of TA certificates may not be appropriate when the
deployment is relying on a security model where the TA certificate
content is considered confidential and only its hash is appropriate
for signaling. ACP nodes SHOULD have a mechanism to select whether
the TA certificate is signaled or not. Assuming that both options
are possible with a specific secure channel protocol.
An ACP secure channel MUST immediately be terminated when the
lifetime of any certificate in the chain used to authenticate the
neighbor expires or becomes revoked. This may not be standard
behavior in secure channel protocols because the certificate
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authentication may only influence the setup of the secure channel in
these protocols, but may not be re-validated during the lifetime of
the secure connection in the absence of this requirement.
When specifying an additional security association protocol for ACP
secure channels beyond those covered in this document, protocol
options SHOULD be eliminated that are not necessary to support
devices that are expected to be able to support the ACP to minimize
implementation complexity. For example, definitions for security
protocols often include old/inferior security options required only
to interoperate with existing devices that will not be able to update
to the currently preferred security options. Such old/inferior
security options do not need to be supported when a security
association protocol is first specified for the ACP, strengthening
the "weakest link" and simplifying ACP implementation overhead.
6.8.3. ACP via IPsec
An ACP node announces its ability to support IPsec, negotiated via
IKEv2, as the ACP secure channel protocol using the "IKEv2"
objective-value in the "AN_ACP" GRASP objective.
The ACP usage of IPsec and IKEv2 mandates a profile with a narrow set
of options of the current standards-track usage guidance for IPsec
[RFC8221] and IKEv2 [RFC8247]. These option result in stringent
security properties and can exclude deprecated/legacy algorithms
because there is no need for interoperability with legacy equipment
for ACP secure channels. Any such backward compatibility would lead
only to increased attack surface and implementation complexity, for
no benefit.
6.8.3.1. Native IPsec
An ACP node that is supporting native IPsec MUST use IPsec in tunnel
mode, negotiated via IKEv2, and with IPv6 payload (e.g., ESP Next
Header of 41). It MUST use local and peer link-local IPv6 addresses
for encapsulation. Manual keying MUST NOT be used, see Section 6.2.
Traffic Selectors are:
TSi = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
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IPsec tunnel mode is required because the ACP will route/forward
packets received from any other ACP node across the ACP secure
channels, and not only its own generated ACP packets. With IPsec
transport mode (and no additional encapsulation header in the ESP
payload), it would only be possible to send packets originated by the
ACP node itself because the IPv6 addresses of the ESP must be the
same as that of the outer IPv6 header.
6.8.3.1.1. RFC8221 (IPsec/ESP)
ACP IPsec implementations MUST comply with [RFC8221] (and its
updates). The requirements from above and this section amend and
superseded its requirements.
The IP Authentication Header (AH) MUST NOT be used (because it does
not provide confidentiality).
For the required ESP encryption algorithms in section 5 of [RFC8221]
the following guidance applies:
* ENCR_NULL AH MUST NOT be used (because it does not provide
confidentiality).
* ENCR_AES_GCM_16 is the only MTI ESP encryption algorithm for ACP
via IPsec/ESP (it is already listed as MUST in [RFC8221]).
* ENCR_AES_CBC with AUTH_HMAC_SHA2_256_128 (as the ESP
authentication algorithm) and ENCR_AES_CCM_8 MAY be supported. If
either provides higher performance than ENCR_AES_GCM_16 it SHOULD
be supported.
* ENCR_CHACHA20_POLY1305 SHOULD be supported at equal or higher
performance than ENCR_AES_GCM_16. If that performance is not
feasible, it MAY be supported.
IKEv2 indicates an order for the offered algorithms. The algorithms
SHOULD be ordered by performance. The first algorithm supported by
both sides is generally chosen.
Explanations:
* There is no requirement to interoperate with legacy equipment in
ACP secure channels, so a single MTI encryption algorithm for
IPsec in ACP secure channels is sufficient for interoperability
and allows for the most lightweight implementations.
* ENCR_AES_GCM_16 is an authenticated encryption with associated
data (AEAD) cipher mode, so no additional ESP authentication
algorithm is needed, simplifying the MTI requirements of IPsec for
the ACP.
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* There is no MTI requirement for the support of ENCR_AES_CBC
because ENCR_AES_GCM_16 is assumed to be feasible with less cost/
higher performance in modern devices hardware accelerated
implementations compared to ENCR-AES_CBC.
* ENCR_CHACHA20_POLY1305 is mandatory in [RFC8221] because of its
target use as a fallback algorithm in case weaknesses in AES are
uncovered. Unfortunately, there is currently no way to
automatically propagate across an ACP a policy to disallow use of
AES based algorithms, so this target benefit of
ENCR_CHACHA20_POLY1305 cannot fully be adopted yet for the ACP.
Therefore, this algorithm is only recommended. Changing from AES
to this algorithm at potentially big drop in performance could
also render the ACP inoperable. Therefore, the performance
requirement against this algorithm so that it could become an
effective security backup to AES for the ACP once a policy to
switch over to it or prefer it is available in an ACP framework.
[RFC8221] allows for 128-bit or 256-bit AES keys. This document
mandates that only 256-bit AES keys MUST be supported.
When [RFC8221] is updated, ACP implementations will need to consider
legacy interoperability, and the IPsec WG has generally done a very
good job of taking that into account in its recommendations.
6.8.3.1.2. RFC8247 (IKEv2)
[RFC8247] provides a baseline recommendation for mandatory to
implement ciphers, integrity checks, pseudo-random-functions and
Diffie-Hellman mechanisms. Those recommendations, and the
recommendations of subsequent documents apply well to the ACP.
Because IKEv2 for ACP secure channels is sufficient to be implemented
in control plane software, rather than in ASIC hardware, and ACP
nodes supporting IKEv2 are not assumed to be code-space constrained,
and because existing IKEv2 implementations are expected to support
[RFC8247] recommendations, this documents makes no attempt to
simplify its recommendations for use with the ACP.
See [IKEV2IANA] for IANA IKEv2 parameter names used in this text.
ACP Nodes supporting IKEv2 MUST comply with [RFC8247] amended by the
following requirements which constitute a policy statement as
permitted by [RFC8247].
To signal the ACP certificate chain (including TA) as required by
Section 6.8.2, "X.509 Certificate - Signature" payload in IKEv2 can
be used. It is mandatory according to [RFC7296] section 3.6.
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ACP nodes SHOULD set up IKEv2 to only use the ACP certificate and TA
when acting as an IKEv2 responder on the IPv6 link local address and
port number indicated in the AN_ACP DULL GRASP announcements (see
Section 6.4).
When CERTREQ is received from a peer, and does not indicate any of
this ACP nodes TA certificates, the ACP node SHOULD ignore the
CERTREQ and continue sending its certificate chain including its TA
as subject to the requirements and explanations in Section 6.8.2.
This will not result in successful mutual authentication but assists
diagnostics.
Note that with IKEv2, failing authentication will only result in the
responder receiving the certificate chain from the initiator, but not
vice versa. Because ACP secure channel setup is symmetric (see
Section 6.7), every non-malicious ACP neighbor will attempt to
connect as an initiator though, allowing to obtain the diagnostic
information about the neighbors certificate.
In IKEv2, ACP nodes are identified by their ACP address. The
ID_IPv6_ADDR IKEv2 identification payload MUST be used and MUST
convey the ACP address. If the peer's ACP certificate includes a
32HEXDIG ACP address in the acp-node-name (not "0" or omitted), the
address in the IKEv2 identification payload MUST match it. See
Section 6.2.3 for more information about "0" or omitted ACP address
fields in the acp-node-name.
IKEv2 authentication MUST use authentication method 14 ("Digital
Signature") for ACP certificates; this authentication method can be
used with both RSA and ECDSA certificates, indicated by an ASN.1
object AlgorithmIdentifier.
The Digital Signature hash SHA2-512 MUST be supported (in addition to
SHA2-256).
The IKEv2 Diffie-Hellman key exchange group 19 (256-bit random ECP),
MUST be supported. Reason: ECC provides a similar security level to
finite-field (MODP) key exchange with a shorter key length, so is
generally preferred absent other considerations.
6.8.3.2. IPsec with GRE encapsulation
In network devices it is often more common to implement high
performance virtual interfaces on top of GRE encapsulation than on
top of a "native" IPsec association (without any other encapsulation
than those defined by IPsec). On those devices it may be beneficial
to run the ACP secure channel on top of GRE protected by the IPsec
association.
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The requirements for ESP/IPsec/IKEv2 with GRE are the same as for
native IPsec (see Section 6.8.3.1) except that IPsec transport mode
and next protocol GRE (47) are to be negotiated. Tunnel mode is not
required because of GRE. Traffic Selectors are:
TSi = (47, 0-65535, Initiator-IPv6-LL-addr ... Initiator-IPv6-LL-
addr)
TSr = (47, 0-65535, Responder-IPv6-LL-addr ... Responder-IPv6-LL-
addr)
If IKEv2 initiator and responder support IPsec over GRE, it will be
preferred over native IPsec because of the way how IKEv2 negotiates
transport mode (as used by this IPsec over GRE profile) versus tunnel
mode as used by native IPsec (see [RFC7296], section 1.3.1). The ACP
IPv6 traffic has to be carried across GRE according to [RFC7676].
6.8.4. ACP via DTLS
This document defines the use of ACP via DTLS, on the assumption that
it is likely the first transport encryption supported in some classes
of constrained devices: DTLS is commonly used in constrained devices
when IPsec is not. Code-space on those devices may be also be too
limited to support more than the minimum number of required
protocols.
An ACP node announces its ability to support DTLS version 1.2
([RFC6347]) compliant with the requirements defined in this document
as an ACP secure channel protocol in GRASP through the "DTLS"
objective-value in the "AN_ACP" objective (see Section 6.4).
To run ACP via UDP and DTLS, a locally assigned UDP port is used that
is announced as a parameter in the GRASP AN_ACP objective to
candidate neighbors. This port can also be any newer version of DTLS
as long as that version can negotiate a DTLS v1.2 connection in the
presence of an DTLS v1.2 only peer.
All ACP nodes supporting DTLS as a secure channel protocol MUST
adhere to the DTLS implementation recommendations and security
considerations of BCP 195, BCP 195 [RFC7525] except with respect to
the DTLS version. ACP nodes supporting DTLS MUST support DTLS 1.2.
They MUST NOT support older versions of DTLS.
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Unlike for IPsec, no attempts are made to simplify the requirements
of the BCP 195 recommendations because the expectation is that DTLS
would be using software-only implementations where the ability to
reuse of widely adopted implementations is more important than
minimizing the complexity of a hardware accelerated implementation
which is known to be important for IPsec.
DTLS v1.3 ([I-D.ietf-tls-dtls13]) is "backward compatible" with DTLS
v1.2 (see section 1. of DTLS v1.3). A DTLS implementation supporting
both DTLS v1.2 and DTLS v1.3 does comply with the above requirements
of negotiating to DTLS v1.2 in the presence of a DTLS v1.2 only peer,
but using DTLS v1.3 when booth peers support it.
Version v1.2 is the MTI version of DTLS in this specification because
* There is more experience with DTLS v1.2 across the spectrum of
target ACP nodes.
* Firmware of lower end, embedded ACP nodes may not support a newer
version for a long time.
* There are significant changes of DTLS v1.3, such as a different
record layer requiring time to gain implementation and deployment
experience especially on lower end, code space limited devices.
* The existing BCP [RFC7525] for DTLS v1.2 may equally take longer
time to be updated with experience from a newer DTLS version.
* There are no significant use-case relevant benefits of DTLS v1.3
over DTLS v1.2 in the context of the ACP options for DTLS. For
example, signaling performance improvements for session setup in
DTLS v1.3 is not important for the ACP given the long-lived nature
of ACP secure channel connections and the fact that DTLS
connections are mostly link-local (short RTT).
Nevertheless, newer versions of DTLS, such as DTLS v1.3 have stricter
security requirements and use of the latest standard protocol version
is for IETF security standards in general recommended. Therefore,
ACP implementations are advised to support all the newer versions of
DTLS that can still negotiate down to DTLS v1.2.
[RFC-editor: if by the time of AUTH48, DTLS 1.3 would have evolved to
be an RFC, then not only would the references to the DTLS v1.3 draft
be changed to the RFC number, but that RFC is then going to be put
into the normative list of references and the above paragraph is
going to be amended to say: Implementations SHOULD support
[DTLSv1.3-RFC]. This is not done right now, because there is no
benefit in potentially waiting in RFC-editor queue for that RFC given
how the text already lays out a non-normative desire to support
DTLSv1.3.]
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There is no additional session setup or other security association
besides this simple DTLS setup. As soon as the DTLS session is
functional, the ACP peers will exchange ACP IPv6 packets as the
payload of the DTLS transport connection. oAny DTLS defined security
association mechanisms such as re-keying are used as they would be
for any transport application relying solely on DTLS.
6.8.5. ACP Secure Channel Profiles
As explained in the beginning of Section 6.6, there is no single
secure channel mechanism mandated for all ACP nodes. Instead, this
section defines two ACP profiles (baseline and constrained) for ACP
nodes that do introduce such requirements.
An ACP node supporting the "baseline" profile MUST support IPsec
natively and MAY support IPsec via GRE. An ACP node supporting the
"constrained" profile node that cannot support IPsec MUST support
DTLS. An ACP node connecting an area of constrained ACP nodes with
an area of baseline ACP nodes needs to support IPsec and DTLS and
supports therefore the baseline and constrained profile.
Explanation: Not all type of ACP nodes can or need to connect
directly to each other or are able to support or prefer all possible
secure channel mechanisms. For example, code space limited IoT
devices may only support DTLS because that code exists already on
them for end-to-end security, but high-end core routers may not want
to support DTLS because they can perform IPsec in accelerated
hardware but would need to support DTLS in an underpowered CPU
forwarding path shared with critical control plane operations. This
is not a deployment issue for a single ACP across these type of nodes
as long as there are also appropriate gateway ACP nodes that support
sufficiently many secure channel mechanisms to allow interconnecting
areas of ACP nodes with a more constrained set of secure channel
protocols. On the edge between IoT areas and high-end core networks,
general-purpose routers that act as those gateways and that can
support a variety of secure channel protocols is the norm already.
IPsec natively with tunnel mode provides the shortest encapsulation
overhead. GRE may be preferred by legacy implementations because the
virtual interfaces required by ACP design in conjunction with secure
channels have in the past more often been implemented for GRE than
purely for native IPsec.
ACP nodes need to specify in documentation the set of secure ACP
mechanisms they support and should declare which profile they support
according to above requirements.
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6.9. GRASP in the ACP
6.9.1. GRASP as a core service of the ACP
The ACP MUST run an instance of GRASP inside of it. It is a key part
of the ACP services. The function in GRASP that makes it fundamental
as a service of the ACP is the ability to provide ACP wide service
discovery (using objectives in GRASP).
ACP provides IP unicast routing via the RPL routing protocol (see
Section 6.12).
The ACP does not use IP multicast routing nor does it provide generic
IP multicast services (the handling of GRASP link-local multicast
messages is explained in Section 6.9.2). Instead, the ACP provides
service discovery via the objective discovery/announcement and
negotiation mechanisms of the ACP GRASP instance (services are a form
of objectives). These mechanisms use hop-by-hop reliable flooding of
GRASP messages for both service discovery (GRASP M_DISCOVERY
messages) and service announcement (GRASP M_FLOOD messages).
See Appendix A.5 for discussion about this design choice of the ACP.
6.9.2. ACP as the Security and Transport substrate for GRASP
In the terminology of GRASP ([I-D.ietf-anima-grasp]), the ACP is the
security and transport substrate for the GRASP instance run inside
the ACP ("ACP GRASP").
This means that the ACP is responsible for ensuring that this
instance of GRASP is only sending messages across the ACP GRASP
virtual interfaces. Whenever the ACP adds or deletes such an
interface because of new ACP secure channels or loss thereof, the ACP
needs to indicate this to the ACP instance of GRASP. The ACP exists
also in the absence of any active ACP neighbors. It is created when
the node has a domain certificate, and continues to exist even if all
of its neighbors cease operation.
In this case ASAs using GRASP running on the same node would still
need to be able to discover each other's objectives. When the ACP
does not exist, ASAs leveraging the ACP instance of GRASP via APIs
MUST still be able to operate, and MUST be able to understand that
there is no ACP and that therefore the ACP instance of GRASP cannot
operate.
The following explanation how ACP acts as the security and transport
substrate for GRASP is visualized in Figure 9 below.
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GRASP unicast messages inside the ACP always use the ACP address.
Link-local addresses from the ACP VRF MUST NOT be used inside
objectives. GRASP unicast messages inside the ACP are transported
via TLS. See Section 6.1 for TLS requirements. TLS mutual
authentication MUST use the ACP domain membership check defined in
(Section 6.2.3).
GRASP link-local multicast messages are targeted for a specific ACP
virtual interface (as defined Section 6.13.5) but are sent by the ACP
into an ACP GRASP virtual interface that is constructed from the TCP
connection(s) to the IPv6 link-local neighbor address(es) on the
underlying ACP virtual interface. If the ACP GRASP virtual interface
has two or more neighbors, the GRASP link-local multicast messages
are replicated to all neighbor TCP connections.
TCP and TLS connections for GRASP in the ACP use the IANA assigned
TCP port for GRASP (7107). Effectively the transport stack is
expected to be TLS for connections from/to the ACP address (e.g.,
global scope address(es)) and TCP for connections from/to link-local
addresses on the ACP virtual interfaces. The latter ones are only
used for flooding of GRASP messages.
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..............................ACP..............................
. .
. /-GRASP-flooding-\ ACP GRASP instance .
. / \ A
. GRASP GRASP GRASP C
. link-local unicast link-local P
. multicast messages multicast .
. messages | messages .
. | | | .
...............................................................
. v v v ACP security and transport .
. | | | substrate for GRASP .
. | | | .
. | ACP GRASP | - ACP GRASP A
. | Loopback | Loopback interface C
. | interface | - ACP-cert auth P
. | TLS | .
. ACP GRASP | ACP GRASP - ACP GRASP virtual .
. subnet1 | subnet2 virtual interfaces .
. TCP | TCP .
. | | | .
...............................................................
. | | | ^^^ Users of ACP (GRASP/ASA) .
. | | | ACP interfaces/addressing .
. | | | .
. | | | A
. | ACP-Loopback Interf.| <- ACP Loopback interface C
. | ACP-address | - address (global ULA) P
. subnet1 | subnet2 <- ACP virtual interfaces .
. link-local | link-local - link-local addresses .
...............................................................
. | | | ACP VRF .
. | RPL-routing | virtual routing and forwarding .
. | /IP-Forwarding\ | A
. | / \ | C
. ACP IPv6 packets ACP IPv6 packets P
. |/ \| .
. IPsec/DTLS IPsec/DTLS - ACP-cert auth .
...............................................................
| | Data-Plane
| |
| | - ACP secure channel
link-local link-local - encapsulation addresses
subnet1 subnet2 - Data-Plane interfaces
| |
ACP-Nbr1 ACP-Nbr2
Figure 9: ACP as security and transport substrate for GRASP
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6.9.2.1. Discussion
TCP encapsulation for GRASP M_DISCOVERY and M_FLOOD link local
messages is used because these messages are flooded across
potentially many hops to all ACP nodes and a single link with even
temporary packet loss issues (e.g., WiFi/Powerline link) can reduce
the probability for loss free transmission so much that applications
would want to increase the frequency with which they send these
messages. Such shorter periodic retransmission of datagrams would
result in more traffic and processing overhead in the ACP than the
hop-by-hop reliable retransmission mechanism by TCP and duplicate
elimination by GRASP.
TLS is mandated for GRASP non-link-local unicast because the ACP
secure channel mandatory authentication and encryption protects only
against attacks from the outside but not against attacks from the
inside: Compromised ACP members that have (not yet) been detected and
removed (e.g., via domain certificate revocation / expiry).
If GRASP peer connections were to use just TCP, compromised ACP
members could simply eavesdrop passively on GRASP peer connections
for whom they are on-path ("man in the middle" - MITM) or intercept
and modify them. With TLS, it is not possible to completely
eliminate problems with compromised ACP members, but attacks are a
lot more complex:
Eavesdropping/spoofing by a compromised ACP node is still possible
because in the model of the ACP and GRASP, the provider and consumer
of an objective have initially no unique information (such as an
identity) about the other side which would allow them to distinguish
a benevolent from a compromised peer. The compromised ACP node would
simply announce the objective as well, potentially filter the
original objective in GRASP when it is a MITM and act as an
application level proxy. This of course requires that the
compromised ACP node understand the semantics of the GRASP
negotiation to an extent that allows it to proxy it without being
detected, but in an ACP environment this is quite likely public
knowledge or even standardized.
The GRASP TLS connections are run the same as any other ACP traffic
through the ACP secure channels. This leads to double
authentication/encryption, which has the following benefits:
* Secure channel methods such as IPsec may provide protection
against additional attacks, for example reset-attacks.
* The secure channel method may leverage hardware acceleration and
there may be little or no gain in eliminating it.
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* There is no different security model for ACP GRASP from other ACP
traffic. Instead, there is just another layer of protection
against certain attacks from the inside which is important due to
the role of GRASP in the ACP.
6.10. Context Separation
The ACP is in a separate context from the normal Data-Plane of the
node. This context includes the ACP channels' IPv6 forwarding and
routing as well as any required higher layer ACP functions.
In classical network system, a dedicated VRF is one logical
implementation option for the ACP. If possible by the systems
software architecture, separation options that minimize shared
components are preferred, such as a logical container or virtual
machine instance. The context for the ACP needs to be established
automatically during bootstrap of a node. As much as possible it
should be protected from being modified unintentionally by ("Data-
Plane") configuration.
Context separation improves security, because the ACP is not
reachable from the Data-Plane routing or forwarding table(s). Also,
configuration errors from the Data-Plane setup do not affect the ACP.
6.11. Addressing inside the ACP
The channels explained above typically only establish communication
between two adjacent nodes. In order for communication to happen
across multiple hops, the autonomic control plane requires ACP
network wide valid addresses and routing. Each ACP node creates a
Loopback interface with an ACP network wide unique address (prefix)
inside the ACP context (as explained in in Section 6.10). This
address may be used also in other virtual contexts.
With the algorithm introduced here, all ACP nodes in the same routing
subdomain have the same /48 ULA prefix. Conversely, ULA global IDs
from different domains are unlikely to clash, such that two ACP
networks can be merged, as long as the policy allows that merge. See
also Section 10.1 for a discussion on merging domains.
Links inside the ACP only use link-local IPv6 addressing, such that
each node's ACP only requires one routable address prefix.
6.11.1. Fundamental Concepts of Autonomic Addressing
* Usage: Autonomic addresses are exclusively used for self-
management functions inside a trusted domain. They are not used
for user traffic. Communications with entities outside the
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trusted domain use another address space, for example normally
managed routable address space (called "Data-Plane" in this
document).
* Separation: Autonomic address space is used separately from user
address space and other address realms. This supports the
robustness requirement.
* Loopback-only: Only ACP Loopback interfaces (and potentially those
configured for "ACP connect", see Section 8.1) carry routable
address(es); all other interfaces (called ACP virtual interfaces)
only use IPv6 link local addresses. The usage of IPv6 link local
addressing is discussed in [RFC7404].
* Use-ULA: For Loopback interfaces of ACP nodes, we use ULA with L=1
(as defined in section 3.1 of [RFC4193]). Note that the random
hash for ACP Loopback addresses uses the definition in
Section 6.11.2 and not the one of [RFC4193] section 3.2.2.
* No external connectivity: They do not provide access to the
Internet. If a node requires further reaching connectivity, it
should use another, traditionally managed address scheme in
parallel.
* Addresses in the ACP are permanent, and do not support temporary
addresses as defined in [RFC4941].
* Addresses in the ACP are not considered sensitive on privacy
grounds because ACP nodes are not expected to be end-user hosts
and ACP addresses do therefore not represent end-users or groups
of end-users. All ACP nodes are in one (potentially federated)
administrative domain. They are assumed to be to be candidate
hosts of ACP traffic amongst each other or transit thereof. There
are no transit nodes less privileged to know about the identity of
other hosts in the ACP. Therefore, ACP addresses do not need to
be pseudo-random as discussed in [RFC7721]. Because they are not
propagated to untrusted (non ACP) nodes and stay within a domain
(of trust), we also consider them not to be subject to scanning
attacks.
The ACP is based exclusively on IPv6 addressing, for a variety of
reasons:
* Simplicity, reliability and scale: If other network layer
protocols were supported, each would have to have its own set of
security associations, routing table and process, etc.
* Autonomic functions do not require IPv4: Autonomic functions and
autonomic service agents are new concepts. They can be
exclusively built on IPv6 from day one. There is no need for
backward compatibility.
* OAM protocols do not require IPv4: The ACP may carry OAM
protocols. All relevant protocols (SNMP, TFTP, SSH, SCP, RADIUS,
Diameter, NETCONF ...) are available in IPv6. See also [RFC8368]
for how ACP could be made to interoperate with IPv4 only OAM.
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Further explanation about the addressing and routing related reasons
for the choice of the autonomous ACP addressing can be found in
Section 6.13.5.1.
6.11.2. The ACP Addressing Base Scheme
The Base ULA addressing scheme for ACP nodes has the following
format:
8 40 2 78
+--+-------------------------+------+------------------------------+
|fd| hash(routing-subdomain) | Type | (sub-scheme) |
+--+-------------------------+------+------------------------------+
Figure 10: ACP Addressing Base Scheme
The first 48-bits follow the ULA scheme, as defined in [RFC4193], to
which a type field is added:
* "fd" identifies a locally defined ULA address.
* The 40-bits ULA "global ID" (term from [RFC4193]) for ACP
addresses carried in the acp-node-name in the ACP certificates are
the first 40-bits of the SHA256 hash of the routing subdomain from
the same acp-node-name. In the example of Section 6.2.2, the
routing subdomain is "area51.research.acp.example.com" and the
40-bits ULA "global ID" 89b714f3db.
* When creating a new routing-subdomain for an existing autonomic
network, it MUST be ensured, that rsub is selected so the
resulting hash of the routing-subdomain does not collide with the
hash of any pre-existing routing-subdomains of the autonomic
network. This ensures that ACP addresses created by registrars
for different routing subdomains do not collide with each other.
* To allow for extensibility, the fact that the ULA "global ID" is a
hash of the routing subdomain SHOULD NOT be assumed by any ACP
node during normal operations. The hash function is only executed
during the creation of the certificate. If BRSKI is used, then
the BRSKI registrar will create the acp-node-name in response to
the EST Certificate Signing Request (CSR) Attribute Request
message by the pledge.
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* Establishing connectivity between different ACP (different acp-
domain-name) is outside the scope of this specification. If it is
being done through future extensions, then the rsub of all
routing-subdomains across those autonomic networks need to be
selected so the resulting routing-subdomain hashes do not collide.
For example, a large cooperation with its own private TA may want
to create different autonomic networks that initially should not
be able to connect but where the option to do so should be kept
open. When taking this future possibility into account, it is
easy to always select rsub so that no collisions happen.
* Type: This field allows different address sub-schemes. This
addresses the "upgradability" requirement. Assignment of types
for this field will be maintained by IANA.
The sub-scheme may imply a range or set of addresses assigned to the
node, this is called the ACP address range/set and explained in each
sub-scheme.
Please refer to Section 6.11.7 and Appendix A.1 for further
explanations why the following Sub-Addressing schemes are used and
why multiple are necessary.
The following summarizes the addressing Sub-Schemes:
+------+-----------------+-----------+-------------------+
| Type | Name |F-bit| Z | V-bits | Prefix |
+------+-----------------+-----+-----+----------+--------+
| 0x00 | ACP-Zone | N/A | 0 | 1 bit | /127 |
+------+-----------------+-----+-----+----------+--------+
| 0x00 | ACP-Manual | N/A | 1 | N/A | /64 |
+------+-----------------+-----+-----+----------+--------+
| 0x01 | ACP-VLong-8 | 0 | N/A | 8 bits | /120 |
+------+-----------------+-----+-----+----------+--------+
| 0x01 | ACP-VLong-16 | 1 | N/A | 16 bits | /112 |
+------+-----------------+-----+-----+----------+--------+
| 0x10 | Reserved / For future definition/allocation |
+------+-----------------+-----+-----+----------+--------+
| 0x11 | Reserved / For future definition/allocation |
+------+-----------------+-----+-----+----------+--------+
Figure 11: Addressing Sub-Schemes
F-Bit and Z are two encoding fields explained below for the Sub-
Schemes that introduce/use them. V-bits is the number of bits of
addresses allocated to the ACP node. Prefix is the prefix the ACP
node is announcing into the RPL routing protocol.
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6.11.3. ACP Zone Addressing Sub-Scheme (ACP-Zone)
This sub-scheme is used when the Type field of the base scheme is
0x00 and the Z bit is 0x0.
64 64
+-----------------+---+---------++-----------------------------+---+
| (base scheme) | Z | Zone-ID || Node-ID |
| | | || Registrar-ID | Node-Number| V |
+-----------------+---+---------++--------------+--------------+---+
50 1 13 48 15 1
Figure 12: ACP Zone Addressing Sub-Scheme
The fields are defined as follows:
* Type: MUST be 0x0.
* Z: MUST be 0x0.
* Zone-ID: A value for a network zone.
* Node-ID: A unique value for each node.
The 64-bit Node-ID must be unique across the ACP domain for each
node. It is derived and composed as follows:
* Registrar-ID (48-bit): A number unique inside the domain that
identifies the ACP registrar which assigned the Node-ID to the
node. One or more domain-wide unique identifiers of the ACP
registrar can be used for this purpose. See Section 6.11.7.2.
* Node-Number: Number to make the Node-ID unique. This can be
sequentially assigned by the ACP Registrar owning the Registrar-
ID.
* V (1-bit): Virtualization bit: 0: Indicates the ACP itself ("ACP
node base system); 1: Indicates the optional "host" context on the
ACP node (see below).
In the ACP Zone Addressing Sub-Scheme, the ACP address in the
certificate has V field as all zero bits.
The ACP address set of the node includes addresses with any Zone-ID
value and any V value. No two nodes in the same ACP can have the
same Node-ID, but different Zone-IDs.
The Virtual bit in this sub-scheme allows the easy addition of the
ACP as a component to existing systems without causing problems in
the port number space between the services in the ACP and the
existing system. V:0 is the ACP router (autonomic node base system),
V:1 is the host with pre-existing transport endpoints on it that
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could collide with the transport endpoints used by the ACP router.
The ACP host could for example have a p2p virtual interface with the
V:0 address as its router into the ACP. Depending on the software
design of ASAs, which is outside the scope of this specification,
they may use the V:0 or V:1 address.
The location of the V bit(s) at the end of the address allows the
announcement of a single prefix for each ACP node. For example, in a
network with 20,000 ACP nodes, this avoid 20,000 additional routes in
the routing table.
It is RECOMMENDED that only Zone-ID 0 is used unless it is meant to
be used in conjunction with operational practices for partial/
incremental adoption of the ACP as described in Section 9.4.
Note: Zones and Zone-ID as defined here are not related to [RFC4007]
zones or zone_id. ACP zone addresses are not scoped (reachable only
from within an RFC4007 zone) but reachable across the whole ACP. An
RFC4007 zone_id is a zone index that has only local significance on a
node, whereas an ACP Zone-ID is an identifier for an ACP zone that is
unique across that ACP.
6.11.4. ACP Manual Addressing Sub-Scheme (ACP-Manual)
This sub-scheme is used when the Type field of the base scheme is
0x00 and the Z bit is 0x1.
64 64
+---------------------+---+----------++-----------------------------+
| (base scheme) | Z | Subnet-ID|| Interface Identifier |
+---------------------+---+----------++-----------------------------+
50 1 13
Figure 13: ACP Manual Addressing Sub-Scheme
The fields are defined as follows:
* Type: MUST be 0x0.
* Z: MUST be 0x1.
* Subnet-ID: Configured subnet identifier.
* Interface Identifier.
This sub-scheme is meant for "manual" allocation to subnets where the
other addressing schemes cannot be used. The primary use case is for
assignment to ACP connect subnets (see Section 8.1.1).
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"Manual" means that allocations of the Subnet-ID need to be done
today with pre-existing, non-autonomic mechanisms. Every subnet that
uses this addressing sub-scheme needs to use a unique Subnet-ID
(unless some anycast setup is done).
The Z bit field was added to distinguish Zone addressing and manual
addressing sub-schemes without requiring one more bit in the base
scheme and therefore allowing for the Vlong scheme (described below)
to have one more bit available.
Manual addressing sub-scheme addresses SHOULD NOT be used in ACP
certificates. Any node capable to build ACP secure channels and
permitted by Registrar policy to participate in building ACP secure
channels SHOULD receive an ACP address (prefix) from one of the other
ACP addressing sub-schemes. Nodes not capable (or permitted) to
participate in ACP secure channels can connect to the ACP via ACP
connect interfaces of ACP edge nodes (see Section 8.1), without
setting up an ACP secure channel. Their ACP certificate MUST omit
the acp-address field to indicate that their ACP certificate is only
usable for non- ACP secure channel authentication, such as end-to-end
transport connections across the ACP or Data-Plane.
Address management of ACP connect subnets is done using traditional
assignment methods and existing IPv6 protocols. See Section 8.1.3
for details. Therefore, the notion of V-bit many addresses assigned
to the ACP nodes does not apply to this Sub-Scheme.
6.11.5. ACP Vlong Addressing Sub-Scheme (ACP-VLong-8/ACP-VLong-16
This sub-scheme is used when the Type field of the base scheme is
0x01.
50 78
+---------------------++-----------------------------+----------+
| (base scheme) || Node-ID |
| || Registrar-ID |F| Node-Number| V |
+---------------------++--------------+--------------+----------+
50 46 1 23/15 8/16
Figure 14: ACP Vlong Addressing Sub-Scheme
This addressing scheme foregoes the Zone-ID field to allow for
larger, flatter routed networks (e.g., as in IoT) with 8421376 Node-
Numbers (2^23+2^15). It also allows for up to 2^16 (i.e. 65536)
different virtualized addresses within a node, which could be used to
address individual software components in an ACP node.
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The fields are the same as in the Zone-ID sub-scheme with the
following refinements:
* F: format bit. This bit determines the format of the subsequent
bits.
* V: Virtualization bit: this is a field that is either 8 or 16
bits. For F=0, it is 8 bits, for F=1 it is 16 bits. The V bits
are assigned by the ACP node. In the ACP certificate's ACP
address Section 6.2.2, the V-bits are always set to 0.
* Registrar-ID: To maximize Node-Number and V, the Registrar-ID is
reduced to 46-bits. One or more domain-wide unique identifiers of
the ACP registrar can be used for this purpose. See
Section 6.11.7.2.
* The Node-Number is unique to each ACP node. There are two formats
for the Node-Number. When F=0, the node-number is 23 bits, for
F=1 it is 15 bits. Each format of node-number is considered to be
in a unique number space.
The F=0 bit format addresses are intended to be used for "general
purpose" ACP nodes that would potentially have a limited number (<
256) of clients (ASA/Autonomic Functions or legacy services) of the
ACP that require separate V(irtual) addresses.
The F=1 bit Node-Numbers are intended for ACP nodes that are ACP edge
nodes (see Section 8.1.1) or that have a large number of clients
requiring separate V(irtual) addresses. For example, large SDN
controllers with container modular software architecture (see
Section 8.1.2).
In the Vlong addressing sub-scheme, the ACP address in the
certificate has all V field bits as zero. The ACP address set for
the node includes any V value.
6.11.6. Other ACP Addressing Sub-Schemes
Before further addressing sub-schemes are defined, experience with
the schemes defined here should be collected. The schemes defined in
this document have been devised to allow hopefully sufficiently
flexible setup of ACPs for a variety of situation. These reasons
also lead to the fairly liberal use of address space: The Zone
Addressing Sub-Scheme is intended to enable optimized routing in
large networks by reserving bits for Zone-ID's. The Vlong addressing
sub-scheme enables the allocation of 8/16-bit of addresses inside
individual ACP nodes. Both address spaces allow distributed,
uncoordinated allocation of node addresses by reserving bits for the
registrar-ID field in the address.
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6.11.7. ACP Registrars
ACP registrars are responsible to enroll candidate ACP nodes with ACP
certificates and associated trust anchor(s). They are also
responsible that an acp-node-name field is included in the ACP
certificate carrying the ACP domain name and the ACP nodes ACP
address prefix. This address prefix is intended to persist unchanged
through the lifetime of the ACP node.
Because of the ACP addressing sub-schemes, an ACP domain can have
multiple distributed ACP registrars that do not need to coordinate
for address assignment. ACP registrars can also be sub-CAs, in which
case they can also assign ACP certificates without dependencies
against a (shared) TA (except during renewals of their own
certificates).
ACP registrars are PKI registration authorities (RA) enhanced with
the handling of the ACP certificate specific fields. They request
certificates for ACP nodes from a Certification Authority through any
appropriate mechanism (out of scope in this document, but required to
be BRSKI for ANI registrars). Only nodes that are trusted to be
compliant with the requirements against registrar described in this
section can be given the necessary credentials to perform this RA
function, such as credentials for the BRSKI connection to the CA for
ANI registrars.
6.11.7.1. Use of BRSKI or other Mechanism/Protocols
Any protocols or mechanisms may be used by ACP registrars, as long as
the resulting ACP certificate and TA certificate(s) allow to perform
the ACP domain membership described in Section 6.2.3 with other ACP
domain members, and meet the ACP addressing requirements for its acp-
node-name as described further below in this section.
An ACP registrar could be a person deciding whether to enroll a
candidate ACP node and then orchestrating the enrollment of the ACP
certificate and associated TA, using command line or web based
commands on the candidate ACP node and TA to generate and sign the
ACP certificate and configure certificate and TA onto the node.
The only currently defined protocol for ACP registrars is BRSKI
([I-D.ietf-anima-bootstrapping-keyinfra]). When BRSKI is used, the
ACP nodes are called ANI nodes, and the ACP registrars are called
BRSKI or ANI registrars. The BRSKI specification does not define the
handling of the acp-node-name field because the rules do not depend
on BRSKI but apply equally to any protocols/mechanisms an ACP
registrar may use.
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6.11.7.2. Unique Address/Prefix allocation
ACP registrars MUST NOT allocate ACP address prefixes to ACP nodes
via the acp-node-name that would collide with the ACP address
prefixes of other ACP nodes in the same ACP domain. This includes
both prefixes allocated by the same ACP registrar to different ACP
nodes as well as prefixes allocated by other ACP registrars for the
same ACP domain.
To support such unique address allocation, an ACP registrar MUST have
one or more 46-bit identifiers unique across the ACP domain which is
called the Registrar-ID. Allocation of Registrar-ID(s) to an ACP
registrar can happen through OAM mechanisms in conjunction with some
database / allocation orchestration.
ACP registrars running on physical devices with known globally unique
EUI-48 MAC address(es) can use the lower 46 bits of those address(es)
as unique Registrar-IDs without requiring any external signaling/
configuration (the upper two bits, V and U are not uniquely assigned
but functional). This approach is attractive for distributed, non-
centrally administered, lightweight ACP registrar implementations.
There is no mechanism to deduce from a MAC address itself whether it
is actually uniquely assigned. Implementations need to consult
additional offline information before making this assumption. For
example by knowing that a particular physical product/MIC-chip is
guaranteed to use globally unique assigned EUI-48 MAC address(es).
When the candidate ACP device (called Pledge in BRSKI) is to be
enrolled into an ACP domain, the ACP registrar needs to allocate a
unique ACP address to the node and ensure that the ACP certificate
gets a acp-node-name field (Section 6.2.2) with the appropriate
information - ACP domain-name, ACP-address, and so on. If the ACP
registrar uses BRSKI, it signals the ACP acp-node-name field to the
Pledge via the EST /csrattrs command (see
[I-D.ietf-anima-bootstrapping-keyinfra], section 5.9.2 - "EST CSR
Attributes").
[RFC-Editor: please update reference to section 5.9.2 accordingly
with latest BRSKI draft at time of publishing, or RFC]
6.11.7.3. Addressing Sub-Scheme Policies
The ACP registrar selects for the candidate ACP node a unique address
prefix from an appropriate ACP addressing sub-scheme, either a zone
addressing sub-scheme prefix (see Section 6.11.3), or a Vlong
addressing sub-scheme prefix (see Section 6.11.5). The assigned ACP
address prefix encoded in the acp-node-name field of the ACP
certificate indicates to the ACP node its ACP address information.
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The sub-addressing scheme indicates the prefix length: /127 for zone
address sub-scheme, /120 or /112 for Vlong address sub-scheme. The
first address of the prefix is the ACP address. All other addresses
in the prefix are for other uses by the ACP node as described in the
zone and Vlong addressing sub scheme sections. The ACP address
prefix itself is then signaled by the ACP node into the ACP routing
protocol (see Section 6.12) to establish IPv6 reachability across the
ACP.
The choice of addressing sub-scheme and prefix-length in the Vlong
address sub-scheme is subject to ACP registrar policy. It could be
an ACP domain wide policy, or a per ACP node or per ACP node type
policy. For example, in BRSKI, the ACP registrar is aware of the
IDevID certificate of the candidate ACP node, which typically
contains a "serialNumber" attribute in the subject field
distinguished name encoding that is often indicating the node's
vendor and device type and can be used to drive a policy selecting an
appropriate addressing sub-scheme for the (class of) node(s).
ACP registrars SHOULD default to allocate ACP zone sub-address scheme
addresses with Zone-ID 0.
ACP registrars that are aware of the IDevID certificate of a
candidate ACP device SHOULD be able to choose the zone vs. Vlong sub-
address scheme for ACP nodes based on the [X.520] "serialNumber"
attribute in the subject field distinguished name encoding of the
IDevID certificate, for example by the PID (Product Identifier) part
which identifies the product type, or the complete "serialNumber".
The PID for example could identify nodes that allow for specialized
ASA requiring multiple addresses or non-autonomic VMs for services
and those nodes could receive Vlong sub-address scheme ACP addresses.
In a simple allocation scheme, an ACP registrar remembers
persistently across reboots its currently used Registrar-ID and for
each addressing scheme (Zone with Zone-ID 0, Vlong with /112, Vlong
with /120), the next Node-Number available for allocation and
increases it during successful enrollment to an ACP node. In this
simple allocation scheme, the ACP registrar would not recycle ACP
address prefixes from no longer used ACP nodes.
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If allocated addresses cannot be remembered by registrars, then it is
necessary to either use a new value for the Register-ID field in the
ACP addresses, or determine allocated ACP addresses from determining
the addresses of reachable ACP nodes, which is not necessarily the
set of all ACP nodes. Non-tracked ACP addresses can be reclaimed by
revoking or not renewing their certificates and instead handing out
new certificate with new addresses (for example with a new Registrar-
ID value). Note that such strategies may require coordination
amongst registrars.
6.11.7.4. Address/Prefix Persistence
When an ACP certificate is renewed or rekeyed via EST or other
mechanisms, the ACP address/prefix in the acp-node-name field MUST be
maintained unless security issues or violations of the unique address
assignment requirements exist or are suspected by the ACP registrar.
ACP address information SHOULD be maintained even when the renewing/
rekeying ACP registrar is not the same as the one that enrolled the
prior ACP certificate. See Section 9.2.4 for an example.
ACP address information SHOULD also be maintained even after an ACP
certificate did expire or failed. See Section 6.2.5.5 and
Section 6.2.5.6.
6.11.7.5. Further Details
Section 9.2 discusses further informative details of ACP registrars:
What interactions registrars need, what parameters they require,
certificate renewal and limitations, use of sub-CAs on registrars and
centralized policy control.
6.12. Routing in the ACP
Once ULA address are set up all autonomic entities should run a
routing protocol within the autonomic control plane context. This
routing protocol distributes the ULA created in the previous section
for reachability. The use of the autonomic control plane specific
context eliminates the probable clash with Data-Plane routing tables
and also secures the ACP from interference from the configuration
mismatch or incorrect routing updates.
The establishment of the routing plane and its parameters are
automatic and strictly within the confines of the autonomic control
plane. Therefore, no explicit configuration is required.
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All routing updates are automatically secured in transit as the
channels of the ACP are encrypted, and this routing runs only inside
the ACP.
The routing protocol inside the ACP is RPL ([RFC6550]). See
Appendix A.4 for more details on the choice of RPL.
RPL adjacencies are set up across all ACP channels in the same domain
including all its routing subdomains. See Appendix A.6 for more
details.
6.12.1. ACP RPL Profile
The following is a description of the RPL profile that ACP nodes need
to support by default. The format of this section is derived from
[I-D.ietf-roll-applicability-template].
6.12.1.1. Overview
RPL Packet Information (RPI) defined in [RFC6550], section 11.2
defines the data packet artefacts required or beneficial in
forwarding of packets routed by RPL. This profile does not use RPI
for better compatibility with accelerated hardware forwarding planes
which most often does not support the Hop-by-Hop headers used for
RPI, but also to avoid the overhead of the RPI header on the wire and
cost of adding/removing them.
6.12.1.1.1. Single Instance
To avoid the need for RPI, the ACP RPL profile uses a simple
destination prefix based routing/forwarding table. To achieve this,
the profiles uses only one RPL instanceID. This single instanceID
can contain only one Destination Oriented Directed Acyclic Graph
(DODAG), and the routing/forwarding table can therefore only
calculate a single class of service ("best effort towards the primary
NOC/root") and cannot create optimized routing paths to accomplish
latency or energy goals between any two nodes.
This choice is a compromise. Consider a network that has multiple
NOCs in different locations. Only one NOC will become the DODAG
root. Traffic to and from other NOCs has to be sent through the
DODAG (shortest path tree) rooted in the primary NOC. Depending on
topology, this can be an annoyance from a latency point of view or
from minimizing network path resources, but this is deemed to be
acceptable given how ACP traffic is "only" network management/control
traffic. See Appendix A.9.4 for more details.
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Using a single instanceID/DODAG does not introduce a single point of
failure, as the DODAG will reconfigure itself when it detects Data-
Plane forwarding failures including choosing a different root when
the primary one fails.
The benefit of this profile, especially compared to other IGPs is
that it does not calculate routes for node reachable through the same
interface as the DODAG root. This RPL profile can therefore scale to
much larger number of ACP nodes in the same amount of compute and
memory than other routing protocols. Especially on nodes that are
leafs of the topology or those close to those leafs.
6.12.1.1.2. Reconvergence
In RPL profiles where RPL Packet Information (RPI, see
Section 6.12.1.13) is present, it is also used to trigger
reconvergence when misrouted, for example looping, packets are
recognized because of their RPI data. This helps to minimize RPL
signaling traffic especially in networks without stable topology and
slow links.
The ACP RPL profile instead relies on quick reconverging the DODAG by
recognizing link state change (down/up) and triggering reconvergence
signaling as described in Section 6.12.1.7. Since links in the ACP
are assumed to be mostly reliable (or have link layer protection
against loss) and because there is no stretch according to
Section 6.12.1.7, loops caused by loss of RPL routing protocol
signaling packets should be exceedingly rare.
In addition, there are a variety of mechanisms possible in RPL to
further avoid temporary loops RECOMMENDED to be used for the ACPL RPL
profile: DODAG Information Objects (DIOs) SHOULD be sent 2 or 3 times
to inform children when losing the last parent. The technique in
[RFC6550] section 8.2.2.6. (Detaching) SHOULD be favored over that
in section 8.2.2.5., (Poisoning) because it allows local
connectivity. Nodes SHOULD select more than one parent, at least 3
if possible, and send Destination Advertisement Objects (DAO)s to all
of them in parallel.
Additionally, failed ACP tunnels can be quickly discovered trough the
secure channel protocol mechanisms such as IKEv2 Dead Peer Detection.
This can function as a replacement for a Low-power and Lossy
Networks' (LLN's) Expected Transmission Count (ETX) feature that is
not used in this profile. A failure of an ACP tunnel should
immediately signal the RPL control plane to pick a different parent.
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6.12.1.2. RPL Instances
Single RPL instance. Default RPLInstanceID = 0.
6.12.1.3. Storing vs. Non-Storing Mode
RPL Mode of Operations (MOP): MUST support mode 2 - "Storing Mode of
Operations with no multicast support". Implementations MAY support
mode 3 ("... with multicast support" as that is a superset of mode
2). Note: Root indicates mode in DIO flow.
6.12.1.4. DAO Policy
Proactive, aggressive DAO state maintenance:
* Use K-flag in unsolicited DAO indicating change from previous
information (to require DAO-ACK).
* Retry such DAO DAO-RETRIES(3) times with DAO- ACK_TIME_OUT(256ms)
in between.
6.12.1.5. Path Metric
Use Hopcount according to [RFC6551]. Note that this is solely for
diagnostic purposes as it is not used by the objective function.
6.12.1.6. Objective Function
Objective Function (OF): Use OF0 [RFC6552]. No use of metric
containers.
rank_factor: Derived from link speed: <= 100Mbps:
LOW_SPEED_FACTOR(5), else HIGH_SPEED_FACTOR(1)
This is a simple rank differentiation between typical "low speed" or
"IoT" links that commonly max out at 100 Mbps and typical
infrastructure links with speeds of 1 Gbps or higher. Given how the
path selection for the ACP focusses only on reachability but not on
path cost optimization, no attempts at finer grained path
optimization are made.
6.12.1.7. DODAG Repair
Global Repair: we assume stable links and ranks (metrics), so there
is no need to periodically rebuild the DODAG. The DODAG version is
only incremented under catastrophic events (e.g., administrative
action).
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Local Repair: As soon as link breakage is detected, the ACP node send
No-Path DAO for all the targets that were reachable only via this
link. As soon as link repair is detected, the ACP node validates if
this link provides a better parent. If so, a new rank is computed by
the ACP node and it sends new DIO that advertise the new rank. Then
it sends a DAO with a new path sequence about itself.
When using ACP multi-access virtual interfaces, local repair can be
triggered directly by peer breakage, see Section 6.13.5.2.2.
stretch_rank: none provided ("not stretched").
Data Path Validation: Not used.
Trickle: Not used.
6.12.1.8. Multicast
Not used yet but possible because of the selected mode of operations.
6.12.1.9. Security
[RFC6550] security not used, substituted by ACP security.
Because the ACP links already include provisions for confidentiality
and integrity protection, their usage at the RPL layer would be
redundant, and so RPL security is not used.
6.12.1.10. P2P communications
Not used.
6.12.1.11. IPv6 address configuration
Every ACP node (RPL node) announces an IPv6 prefix covering the
addresses assigned to the ACP node via the AcpNodeName. The prefix
length depends on the addressing sub-scheme of the acp-address, /127
for Zone Addressing Sub-Scheme and /112 or /120 for Vlong addressing
sub-scheme. See Section 6.11 for more details.
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Every ACP node MUST install a black hole (aka null) route if there
are unused parts of the ACP address space assigned to the ACP node
via its AcpNodeName. This is superseded by longer prefixes assigned
to interfaces for the address space actually used by the node. For
example, when the node has an ACP-VLong-8 address space, it installs
a /120 black hole route. If it then for example only uses the ACP
address (first address from the space), it would assign that address
via a /128 address prefix to the ACP loopback interface (see
Section 6.13.5.1). None of those longer prefixes are announced into
RPL.
For ACP-Manual address prefixes configured on an ACP node, for
example for ACP connect subnets (see Section 8.1.1), the node
announces the /64 subnet prefix.
6.12.1.12. Administrative parameters
Administrative Preference ([RFC6550], 3.2.6 - to become root):
Indicated in DODAGPreference field of DIO message.
* Explicit configured "root": 0b100
* ACP registrar (Default): 0b011
* ACP-connect (non-registrar): 0b010
* Default: 0b001.
6.12.1.13. RPL Packet Information
RPI is not required in the ACP RPL profile for the following reasons.
One RPI option is the RPL Source Routing Header (SRH) [RFC6554] which
is not necessary because the ACP RPL profile uses storing mode where
each hop has the necessary next-hop forwarding information.
The simpler RPL Option header [RFC6553] is also not necessary in this
profile, because it uses a single RPL instance and data path
validation is also not used.
6.12.1.14. Unknown Destinations
Because RPL minimizes the size of the routing and forwarding table,
prefixes reachable through the same interface as the RPL root are not
known on every ACP node. Therefore, traffic to unknown destination
addresses can only be discovered at the RPL root. The RPL root
SHOULD have attach safe mechanisms to operationally discover and log
such packets.
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As this requirement places additional constraints on the Data-Plane
functionality of the RPL root, it does not apply to "normal" nodes
that are not configured to have special functionality (i.e., the
administrative parameter from Section 6.12.1.12 has value 0b001). If
the ACP network is degraded to the point where there are no nodes
that could be configured as root, registrar, or ACP-connect nodes, it
is possible that the RPL root (and thus the ACP as a whole) would be
unable to detect traffic to unknown destinations. However, in the
absence of nodes with administrative preference other than 0b001,
there is also unlikely to be a way to get diagnostic information out
of the ACP, so detection of traffic to unknown destinations would not
be actionable anyway.
6.13. General ACP Considerations
Since channels are by default established between adjacent neighbors,
the resulting overlay network does hop-by-hop encryption. Each node
decrypts incoming traffic from the ACP, and encrypts outgoing traffic
to its neighbors in the ACP. Routing is discussed in Section 6.12.
6.13.1. Performance
There are no performance requirements against ACP implementations
defined in this document because the performance requirements depend
on the intended use case. It is expected that full autonomic node
with a wide range of ASA can require high forwarding plane
performance in the ACP, for example for telemetry. Implementations
of ACP to solely support traditional/SDN style use cases can benefit
from ACP at lower performance, especially if the ACP is used only for
critical operations, e.g., when the Data-Plane is not available. The
design of the ACP as specified in this document is intended to
support a wide range of performance options: It is intended to allow
software-only implementations at potentially low performance, but can
also support high performance options. See [RFC8368] for more
details.
6.13.2. Addressing of Secure Channels
In order to be independent of the Data-Plane routing and addressing,
the GRASP discovered ACP secure channels use IPv6 link local
addresses between adjacent neighbors. Note: Section 8.2 specifies
extensions in which secure channels are configured tunnels operating
over the Data-Plane, so those secure channels cannot be independent
of the Data-Plane.
To avoid that Data-Plane configuration can impact the operations of
the IPv6 (link-local) interface/address used for ACP channels,
appropriate implementation considerations are required. If the IPv6
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interface/link-local address is shared with the Data-Plane, it needs
to be impossible to unconfigure/disable it through configuration.
Instead of sharing the IPv6 interface/link-local address, a separate
(virtual) interface with a separate IPv6 link-local address can be
used. For example, the ACP interface could be run over a separate
MAC address of an underlying L2 (Ethernet) interface. For more
details and options, see Appendix A.9.2.
Note that other (non-ideal) implementation choices may introduce
additional undesired dependencies against the Data-Plane. For
example, shared code and configuration of the secure channel
protocols (IPsec / DTLS).
6.13.3. MTU
The MTU for ACP secure channels MUST be derived locally from the
underlying link MTU minus the secure channel encapsulation overhead.
ACP secure Channel protocols do not need to perform MTU discovery
because they are built across L2 adjacencies - the MTU on both sides
connecting to the L2 connection are assumed to be consistent.
Extensions to ACP where the ACP is for example tunneled need to
consider how to guarantee MTU consistency. This is an issue of
tunnels, not an issue of running the ACP across a tunnel. Transport
stacks running across ACP can perform normal PMTUD (Path MTU
Discovery). Because the ACP is meant to prioritize reliability over
performance, they MAY opt to only expect IPv6 minimum MTU (1280) to
avoid running into PMTUD implementation bugs or underlying link MTU
mismatch problems.
6.13.4. Multiple links between nodes
If two nodes are connected via several links, the ACP SHOULD be
established across every link, but it is possible to establish the
ACP only on a sub-set of links. Having an ACP channel on every link
has a number of advantages, for example it allows for a faster
failover in case of link failure, and it reflects the physical
topology more closely. Using a subset of links (for example, a
single link), reduces resource consumption on the node, because state
needs to be kept per ACP channel. The negotiation scheme explained
in Section 6.6 allows the Decider (the node with the higher ACP
address) to drop all but the desired ACP channels to the Follower -
and the Follower will not re-try to build these secure channels from
its side unless the Decider shows up with a previously unknown GRASP
announcement (e.g., on a different link or with a different address
announced in GRASP).
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6.13.5. ACP interfaces
The ACP VRF has conceptually two type of interfaces: The "ACP
Loopback interface(s)" to which the ACP ULA address(es) are assigned
and the "ACP virtual interfaces" that are mapped to the ACP secure
channels.
6.13.5.1. ACP loopback interfaces
For autonomous operations of the ACP, as described in Section 6 and
Section 7, the ACP node uses the first address from the N bit ACP
prefix (N = 128 - number of Vbits of the ACP address) assigned to the
node. This address is assigned with an address prefix of N or larger
to a loopback interface.
Other addresses from the prefix can be used by the ACP of the node as
desired. The autonomous operations of the ACP does not require
additional global scope IPv6 addresses, they are instead intended for
ASA or non-autonomous functions. Non fully autonomic components of
the ACP such as ACP connect interfaces (see Figure 16) may also
introduce additional global scope IPv6 addresses on other types of
interfaces into the ACP.
[RFC-Editor: please remove this paragraph: Note to reviewers: Please
do not complain again about an obsolete RFC number in the following
paragraph. The text should make it clear that the reference was
chosen to indicate a particular point in time, but not to recommend/
use a particularly obsolete protocol spec.]
The use of loopback interfaces for global scope addresses is common
operational configuration practice on routers, for example in IBGP
connections since BGP4 (see [RFC1654]) or earlier. The ACP adopts
and automates this operational practice.
A loopback interface for use with the ACP as described above is an
interface behaving according to [RFC6724] Section 4., paragraph 2:
Packets sent by the host of the node from the loopback interface
behave as if they are looped back by the interface so that they look
as if they originated from the loopback interface, are then received
by the node and forwarded by it towards the destination.
The word loopback only indicates this behavior, but not the actual
name of the interface type choosen in an actual implementation. A
loopback interface for use with the ACP can be a virtual/software
construct without any associated hardware, or it can be a hardware
interface operating in loopback mode.
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A loopback interface used for the ACP MUST NOT have connectivity to
other nodes.
The following reviews the reasons for the choice of loopback
addresses for ACP addresses is based on the IPv6 address architecture
and common challenges:
1. IPv6 addresses are assigned to interfaces, not nodes. IPv6
continues the IPv4 model that a subnet prefix is associated with
one link, see [RFC4291], Section 2.1.
2. IPv6 implementations commonly do not allow assignment of the same
IPv6 global scope address in the same VRF to more than one
interface.
3. Global scope addresses assigned to interfaces that are connecting
to other nodes (external interfaces) may not be stable addresses
for communications because any such interface could fail due to
reasons external to the node. This could render the addresses
assigned to that interface unusable.
4. If failure of the subnet does not result in bringing down the
interface and making the addresses unusable, it could result in
unreachability of the address because the shortest path to the
node might go through one of the other nodes on the same subnet
which could equally consider the subnet to be operational even
though it is not.
5. Many OAM service implementations on routers cannot deal with more
than one peer address, often because they do already expect that
a single loopback address can be used, especially to provide a
stable address under failure of external interfaces or links.
6. Even when an application supports multiple addresses to a peer,
it can only use one address for a connection at a time with the
most widely deployed transport protocols TCP and UDP. While
[RFC6824] solves this problem, it is not widely adopted for
router OAM services implementations.
7. To completely autonomously assign global scope addresses to
subnets connecting to other nodes, it would be necessary for
every node to have an amount of prefix address space in the order
of the maximum number of subnets that the node could connect to
and then the node would have to negotiate with adjacent nodes
across those subnets whose address space to use for each subnet.
8. Using global scope addresses for subnets between nodes is
unnecessary if those subnets only connect routers, such as ACP
secure channels, because they can communicate to remote nodes via
their global scope loopback addresses. Using global scope
addresses for those extern subnets is therefore wasteful for the
address space and also unnecessarily increasing the size of
routing and forwarding tables, which especially for the ACP is
highly undesirable because it should attempt to minimize the per-
node overhead of the ACP VRF.
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9. For all these reasons, the ACP addressing schemes do not consider
ACP addresses for subnets connecting ACP nodes.
Note that [RFC8402] introduces the term Node-SID to refer to IGP
prefix segments that identify a specific router, for example on a
loopback interface. An ACP loopback address prefix may similarly be
called an ACP Node Identifier.
6.13.5.2. ACP virtual interfaces
Any ACP secure channel to another ACP node is mapped to ACP virtual
interfaces in one of the following ways. This is independent of the
chosen secure channel protocol (IPsec, DTLS or other future protocol
- standards or non-standards).
Note that all the considerations described here are assuming point-
to-point secure channel associations. Mapping multi-party secure
channel associations such as [RFC6407] is out of scope.
6.13.5.2.1. ACP point-to-point virtual interfaces
In this option, each ACP secure channel is mapped into a separate
point-to-point ACP virtual interface. If a physical subnet has more
than two ACP capable nodes (in the same domain), this implementation
approach will lead to a full mesh of ACP virtual interfaces between
them.
When the secure channel protocol determines a peer to be dead, this
SHOULD result in indicating link breakage to trigger RPL DODAG
repair, see Section 6.12.1.7.
6.13.5.2.2. ACP multi-access virtual interfaces
In a more advanced implementation approach, the ACP will construct a
single multi-access ACP virtual interface for all ACP secure channels
to ACP capable nodes reachable across the same underlying (physical)
subnet. IPv6 link-local multicast packets sent into an ACP multi-
access virtual interface are replicated to every ACP secure channel
mapped into the ACP multicast-access virtual interface. IPv6 unicast
packets sent into an ACP multi-access virtual interface are sent to
the ACP secure channel that belongs to the ACP neighbor that is the
next-hop in the ACP forwarding table entry used to reach the packets
destination address.
When the secure channel protocol determines a peer to be dead for a
secure channel mapped into an ACP multi-access virtual interface,
this SHOULD result in signaling breakage of that peer to RPL, so it
can trigger RPL DODAG repair, see Section 6.12.1.7.
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There is no requirement for all ACP nodes on the same multi-access
subnet to use the same type of ACP virtual interface. This is purely
a node local decision.
ACP nodes MUST perform standard IPv6 operations across ACP virtual
interfaces including SLAAC (Stateless Address Auto-Configuration) -
[RFC4862]) to assign their IPv6 link local address on the ACP virtual
interface and ND (Neighbor Discovery - [RFC4861]) to discover which
IPv6 link-local neighbor address belongs to which ACP secure channel
mapped to the ACP virtual interface. This is independent of whether
the ACP virtual interface is point-to-point or multi-access.
"Optimistic Duplicate Address Detection (DAD)" according to [RFC4429]
is RECOMMENDED because the likelihood for duplicates between ACP
nodes is highly improbable as long as the address can be formed from
a globally unique local assigned identifier (e.g., EUI-48/EUI-64, see
below).
ACP nodes MAY reduce the amount of link-local IPv6 multicast packets
from ND by learning the IPv6 link-local neighbor address to ACP
secure channel mapping from other messages such as the source address
of IPv6 link-local multicast RPL messages - and therefore forego the
need to send Neighbor Solicitation messages.
The ACP virtual interface IPv6 link local address can be derived from
any appropriate local mechanism such as node local EUI-48 or EUI-64
("EUI" stands for "Extended Unique Identifier"). It MUST NOT depend
on something that is attackable from the Data-Plane such as the IPv6
link-local address of the underlying physical interface, which can be
attacked by SLAAC, or parameters of the secure channel encapsulation
header that may not be protected by the secure channel mechanism.
The link-layer address of an ACP virtual interface is the address
used for the underlying interface across which the secure tunnels are
built, typically Ethernet addresses. Because unicast IPv6 packets
sent to an ACP virtual interface are not sent to a link-layer
destination address but rather an ACP secure channel, the link-layer
address fields SHOULD be ignored on reception and instead the ACP
secure channel from which the message was received should be
remembered.
Multi-access ACP virtual interfaces are preferable implementations
when the underlying interface is a (broadcast) multi-access subnet
because they do reflect the presence of the underlying multi-access
subnet into the virtual interfaces of the ACP. This makes it for
example simpler to build services with topology awareness inside the
ACP VRF in the same way as they could have been built running
natively on the multi-access interfaces.
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Consider also the impact of point-to-point vs. multi-access virtual
interface on the efficiency of flooding via link local multicasted
messages:
Assume a LAN with three ACP neighbors, Alice, Bob and Carol. Alice's
ACP GRASP wants to send a link-local GRASP multicast message to Bob
and Carol. If Alice's ACP emulates the LAN as per-peer, point-to-
point virtual interfaces, one to Bob and one to Carol, Alice's ACP
GRASP will send two copies of multicast GRASP messages: One to Bob
and one to Carol. If Alice's ACP emulates a LAN via a multipoint
virtual interface, Alice's ACP GRASP will send one packet to that
interface and the ACP multipoint virtual interface will replicate the
packet to each secure channel, one to Bob, one to Carol. The result
is the same. The difference happens when Bob and Carol receive their
packet. If they use ACP point-to-point virtual interfaces, their
GRASP instance would forward the packet from Alice to each other as
part of the GRASP flooding procedure. These packets are unnecessary
and would be discarded by GRASP on receipt as duplicates (by use of
the GRASP Session ID). If Bob and Carol's ACP would emulate a multi-
access virtual interface, then this would not happen, because GRASPs
flooding procedure does not replicate back packets to the interface
that they were received from.
Note that link-local GRASP multicast messages are not sent directly
as IPv6 link-local multicast UDP messages into ACP virtual
interfaces, but instead into ACP GRASP virtual interfaces, that are
layered on top of ACP virtual interfaces to add TCP reliability to
link-local multicast GRASP messages. Nevertheless, these ACP GRASP
virtual interfaces perform the same replication of message and,
therefore, result in the same impact on flooding. See Section 6.9.2
for more details.
RPL does support operations and correct routing table construction
across non-broadcast multi-access (NBMA) subnets. This is common
when using many radio technologies. When such NBMA subnets are used,
they MUST NOT be represented as ACP multi-access virtual interfaces
because the replication of IPv6 link-local multicast messages will
not reach all NBMA subnet neighbors. In result, GRASP message
flooding would fail. Instead, each ACP secure channel across such an
interface MUST be represented as a ACP point-to-point virtual
interface. See also Appendix A.9.4.
Care needs to be taken when creating multi-access ACP virtual
interfaces across ACP secure channels between ACP nodes in different
domains or routing subdomains. If for example future inter-domain
ACP policies are defined as "peer-to-peer" policies, it is easier to
create ACP point-to-point virtual interfaces for these inter-domain
secure channels.
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7. ACP support on L2 switches/ports (Normative)
7.1. Why (Benefits of ACP on L2 switches)
ANrtr1 ------ ANswitch1 --- ANswitch2 ------- ANrtr2
.../ \ \ ...
ANrtrM ------ \ ------- ANrtrN
ANswitchM ...
Figure 15: Topology with L2 ACP switches
Consider a large L2 LAN with ANrtr1...ANrtrN connected via some
topology of L2 switches. Examples include large enterprise campus
networks with an L2 core, IoT networks or broadband aggregation
networks which often have even a multi-level L2 switched topology.
If the discovery protocol used for the ACP is operating at the subnet
level, every ACP router will see all other ACP routers on the LAN as
neighbors and a full mesh of ACP channels will be built. If some or
all of the AN switches are autonomic with the same discovery
protocol, then the full mesh would include those switches as well.
A full mesh of ACP connections can create fundamental scale
challenges. The number of security associations of the secure
channel protocols will likely not scale arbitrarily, especially when
they leverage platform accelerated encryption/decryption. Likewise,
any other ACP operations (such as routing) needs to scale to the
number of direct ACP neighbors. An ACP router with just 4 physical
interfaces might be deployed into a LAN with hundreds of neighbors
connected via switches. Introducing such a new unpredictable scaling
factor requirement makes it harder to support the ACP on arbitrary
platforms and in arbitrary deployments.
Predictable scaling requirements for ACP neighbors can most easily be
achieved if in topologies such as these, ACP capable L2 switches can
ensure that discovery messages terminate on them so that neighboring
ACP routers and switches will only find the physically connected ACP
L2 switches as their candidate ACP neighbors. With such a discovery
mechanism in place, the ACP and its security associations will only
need to scale to the number of physical interfaces instead of a
potentially much larger number of "LAN-connected" neighbors. And the
ACP topology will follow directly the physical topology, something
which can then also be leveraged in management operations or by ASAs.
In the example above, consider ANswitch1 and ANswitchM are ACP
capable, and ANswitch2 is not ACP capable. The desired ACP topology
is that ANrtr1 and ANrtrM only have an ACP connection to ANswitch1,
and that ANswitch1, ANrtr2, ANrtrN have a full mesh of ACP connection
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amongst each other. ANswitch1 also has an ACP connection with
ANswitchM and ANswitchM has ACP connections to anything else behind
it.
7.2. How (per L2 port DULL GRASP)
To support ACP on L2 switches or L2 switched ports of an L3 device,
it is necessary to make those L2 ports look like L3 interfaces for
the ACP implementation. This primarily involves the creation of a
separate DULL GRASP instance/domain on every such L2 port. Because
GRASP has a dedicated link-local IPv6 multicast address
(ALL_GRASP_NEIGHBORS), it is sufficient that all packets for this
address are being extracted at the port level and passed to that DULL
GRASP instance. Likewise the IPv6 link-local multicast packets sent
by that DULL GRASP instance need to be sent only towards the L2 port
for this DULL GRASP instance (instead of being flooded across all
ports of the VLAN to which the port belongs).
When Ports/Interfaces across which the ACP is expected to operate in
an ACP-aware L2-switch or L2/L3-switch/router are L2-bridged, packets
for the ALL_GRASP_NEIGHBORS multicast address MUST never be forward
between these ports. If MLD snooping is used, it MUST be prohibited
from bridging packets for the ALL_GRASP_NEIGHBORS IPv6 multicast
address.
On hybrid L2/L3 switches, multiple L2 ports are assigned to a single
L3 VLAN interface. With the aforementioned changes for DULL GRASP,
ACP can simply operate on the L3 VLAN interfaces, so no further
(hardware) forwarding changes are required to make ACP operate on L2
ports. This is possible because the ACP secure channel protocols
only use link-local IPv6 unicast packets, and these packets will be
sent to the correct L2 port towards the peer by the VLAN logic of the
device.
This is sufficient when p2p ACP virtual interfaces are established to
every ACP peer. When it is desired to create multi-access ACP
virtual interfaces (see Section 6.13.5.2.2), it is REQIURED not to
coalesce all the ACP secure channels on the same L3 VLAN interface,
but only all those on the same L2 port.
If VLAN tagging is used, then all the above described logic only
applies to untagged GRASP packets. For the purpose of ACP neighbor
discovery via GRASP, no VLAN tagged packets SHOULD be sent or
received. In a hybrid L2/L3 switch, each VLAN would therefore only
create ACP adjacencies across those ports where the VLAN is carried
untagged.
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In result, the simple logic is that ACP secure channels would operate
over the same L3 interfaces that present a single flat bridged
network across all routers, but because DULL GRASP is separated on a
per-port basis, no full mesh of ACP secure channels is created, but
only per-port ACP secure channels to per-port L2-adjacent ACP node
neighbors.
For example, in the above picture, ANswitch1 would run separate DULL
GRASP instances on its ports to ANrtr1, ANswitch2 and ANswitchI, even
though all those three ports may be in the data plane in the same
(V)LAN and perform L2 switching between these ports, ANswitch1 would
perform ACP L3 routing between them.
The description in the previous paragraph was specifically meant to
illustrate that on hybrid L3/L2 devices that are common in
enterprise, IoT and broadband aggregation, there is only the GRASP
packet extraction (by Ethernet address) and GRASP link-local
multicast per L2-port packet injection that has to consider L2 ports
at the hardware forwarding level. The remaining operations are
purely ACP control plane and setup of secure channels across the L3
interface. This hopefully makes support for per-L2 port ACP on those
hybrid devices easy.
In devices without such a mix of L2 port/interfaces and L3 interfaces
(to terminate any transport layer connections), implementation
details will differ. Logically most simply every L2 port is
considered and used as a separate L3 subnet for all ACP operations.
The fact that the ACP only requires IPv6 link-local unicast and
multicast should make support for it on any type of L2 devices as
simple as possible.
A generic issue with ACP in L2 switched networks is the interaction
with the Spanning Tree Protocol. Without further L2 enhancements,
the ACP would run only across the active STP topology and the ACP
would be interrupted and re-converge with STP changes. Ideally, ACP
peering SHOULD be built also across ports that are blocked in STP so
that the ACP does not depend on STP and can continue to run
unaffected across STP topology changes, where re-convergence can be
quite slow. The above described simple implementation options are
not sufficient to achieve this.
8. Support for Non-ACP Components (Normative)
8.1. ACP Connect
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8.1.1. Non-ACP Controller / NMS system
The Autonomic Control Plane can be used by management systems, such
as controllers or network management system (NMS) hosts (henceforth
called simply "NMS hosts"), to connect to devices (or other type of
nodes) through it. For this, an NMS host needs to have access to the
ACP. The ACP is a self-protecting overlay network, which allows by
default access only to trusted, autonomic systems. Therefore, a
traditional, non-ACP NMS system does not have access to the ACP by
default, such as any other external node.
If the NMS host is not autonomic, i.e., it does not support autonomic
negotiation of the ACP, then it can be brought into the ACP by
explicit configuration. To support connections to adjacent non-ACP
nodes, an ACP node SHOULD support "ACP connect" (sometimes also
called "autonomic connect"):
"ACP connect" is an interface level configured workaround for
connection of trusted non-ACP nodes to the ACP. The ACP node on
which ACP connect is configured is called an "ACP edge node". With
ACP connect, the ACP is accessible from those non-ACP nodes (such as
NOC systems) on such an interface without those non-ACP nodes having
to support any ACP discovery or ACP channel setup. This is also
called "native" access to the ACP because to those NOC systems the
interface looks like a normal network interface without any ACP
secure channel that is encapsulating the traffic.
Data-Plane "native" (no ACP)
.
+--------+ +----------------+ . +-------------+
| ACP | |ACP Edge Node | . | |
| Node | | | v | |
| |-------|...[ACP VRF]....+----------------| |+
| | ^ |. | | NOC Device ||
| | . | .[Data-Plane]..+----------------| "NMS hosts" ||
| | . | [ ] | . ^ | ||
+--------+ . +----------------+ . . +-------------+|
. . . +-------------+
. . .
Data-Plane "native" . ACP "native" (unencrypted)
+ ACP auto-negotiated . "ACP connect subnet"
and encrypted .
ACP connect interface
e.g., "VRF ACP native" (config)
Figure 16: ACP connect
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ACP connect has security consequences: All systems and processes
connected via ACP connect have access to all ACP nodes on the entire
ACP, without further authentication. Thus, the ACP connect interface
and NOC systems connected to it needs to be physically controlled/
secured. For this reason the mechanisms described here do explicitly
not include options to allow for a non-ACP router to be connected
across an ACP connect interface and addresses behind such a router
routed inside the ACP.
Physical controlled/secured means that attackers can gain no access
to the physical device hosting the ACP Edge Node, the physical
interfaces and links providing the ACP connect link nor the physical
devices hosting the NOC Device. In a simple case, ACP Edge node and
NOC Device are co-located in an access controlled room, such as a
NOC, to which attackers cannot gain physical access.
An ACP connect interface provides exclusively access to only the ACP.
This is likely insufficient for many NMS hosts. Instead, they would
require a second "Data-Plane" interface outside the ACP for
connections between the NMS host and administrators, or Internet
based services, or for direct access to the Data-Plane. The document
"Using Autonomic Control Plane for Stable Connectivity of Network
OAM" [RFC8368] explains in more detail how the ACP can be integrated
in a mixed NOC environment.
An ACP connect interface SHOULD use an IPv6 address/prefix from the
ACP Manual Addressing Sub-Scheme (Section 6.11.4), letting the
operator configure for example only the Subnet-ID and having the node
automatically assign the remaining part of the prefix/address. It
SHOULD NOT use a prefix that is also routed outside the ACP so that
the addresses clearly indicate whether it is used inside the ACP or
not.
The prefix of ACP connect subnets MUST be distributed by the ACP edge
node into the ACP routing protocol RPL. The NMS hosts MUST connect
to prefixes in the ACP routing table via its ACP connect interface.
In the simple case where the ACP uses only one ULA prefix and all ACP
connect subnets have prefixes covered by that ULA prefix, NMS hosts
can rely on [RFC6724] to determine longest match prefix routes
towards its different interfaces, ACP and Data-Plane. With RFC6724,
The NMS host will select the ACP connect interface for all addresses
in the ACP because any ACP destination address is longest matched by
the address on the ACP connect interface. If the NMS hosts ACP
connect interface uses another prefix or if the ACP uses multiple ULA
prefixes, then the NMS hosts require (static) routes towards the ACP
interface for these prefixes.
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When an ACP Edge node receives a packet from an ACP connect
interface, the ACP Edge node MUST only forward the packet into the
ACP if the packet has an IPv6 source address from that interface
(this is sometimes called "RPF filtering"). This filtering rule MAY
be changed through administrative measures. The more any such
administrative action enable reachability of non ACP nodes to the
ACP, the more this may cause security issues.
To limit the security impact of ACP connect, nodes supporting it
SHOULD implement a security mechanism to allow configuration/use of
ACP connect interfaces only on nodes explicitly targeted to be
deployed with it (those in physically secure locations such as a
NOC). For example, the registrar could disable the ability to enable
ACP connect on devices during enrollment and that property could only
be changed through re-enrollment. See also Appendix A.9.5.
ACP Edge nodes SHOULD have a configurable option to prohibit packets
with RPI headers (see Section 6.12.1.13 across an ACP connect
interface. These headers are outside the scope of the RPL profile in
this specification but may be used in future extensions of this
specification.
8.1.2. Software Components
The previous section assumed that ACP Edge node and NOC devices are
separate physical devices and the ACP connect interface is a physical
network connection. This section discusses the implication when
these components are instead software components running on a single
physical device.
The ACP connect mechanism cannot only be used to connect physically
external systems (NMS hosts) to the ACP but also other applications,
containers or virtual machines. In fact, one possible way to
eliminate the security issue of the external ACP connect interface is
to collocate an ACP edge node and an NMS host by making one a virtual
machine or container inside the other; and therefore converting the
unprotected external ACP subnet into an internal virtual subnet in a
single device. This would ultimately result in a fully ACP enabled
NMS host with minimum impact to the NMS hosts software architecture.
This approach is not limited to NMS hosts but could equally be
applied to devices consisting of one or more VNF (virtual network
functions): An internal virtual subnet connecting out-of-band
management interfaces of the VNFs to an ACP edge router VNF.
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The core requirement is that the software components need to have a
network stack that permits access to the ACP and optionally also the
Data-Plane. Like in the physical setup for NMS hosts this can be
realized via two internal virtual subnets. One that is connecting to
the ACP (which could be a container or virtual machine by itself),
and one (or more) connecting into the Data-Plane.
This "internal" use of ACP connect approach should not be considered
to be a "workaround" because in this case it is possible to build a
correct security model: It is not necessary to rely on unprovable
external physical security mechanisms as in the case of external NMS
hosts. Instead, the orchestration of the ACP, the virtual subnets
and the software components can be done by trusted software that
could be considered to be part of the ANI (or even an extended ACP).
This software component is responsible for ensuring that only trusted
software components will get access to that virtual subnet and that
only even more trusted software components will get access to both
the ACP virtual subnet and the Data-Plane (because those ACP users
could leak traffic between ACP and Data-Plane). This trust could be
established for example through cryptographic means such as signed
software packages.
8.1.3. Auto Configuration
ACP edge nodes, NMS hosts and software components that as described
in the previous section are meant to be composed via virtual
interfaces SHOULD support on the ACP connect subnet StateLess Address
Autoconfiguration (SLAAC - [RFC4862]) and route auto configuration
according to [RFC4191].
The ACP edge node acts as the router towards the ACP on the ACP
connect subnet, providing the (auto-)configured prefix for the ACP
connect subnet and (auto-)configured routes into the ACP to NMS hosts
and/or software components.
The ACP edge node uses the Route Information Option (RIO) of RFC4191
to announce aggregated prefixes for address prefixes used in the ACP
(with normal RIO lifetimes. In addition, the ACP edge node also uses
a RIO to announce the default route (::/0) with a lifetime of 0.
These RIOs allow to connect Type C hosts to the ACP via an ACP
connect subnet on one interface and another network (Data Plane / NMS
network) on the same or another interface of the Type C host, relying
on other routers than the ACP edge node. The RIOs ensure that these
hosts will only route the prefixes used in the ACP to the ACP edge
node.
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Type A/B host ignore the RIOs and will consider the ACP node to be
their default router for all destination. This is sufficient when
type A/B hosts only need to connect to the ACP but not to other
networks. Attaching Type A/B hosts to both the ACP and other
networks, requires either explicit ACP prefix route configuration on
the Type A/B hosts or the combined ACP/Data-Plane interface on the
ACP edge node, see Section 8.1.4.
Aggregated prefix means that the ACP edge node needs to only announce
the /48 ULA prefixes used in the ACP but none of the actual /64
(Manual Addressing Sub-Scheme), /127 (ACP Zone Addressing Sub-
Scheme), /112 or /120 (Vlong Addressing Sub-Scheme) routes of actual
ACP nodes. If ACP interfaces are configured with non ULA prefixes,
then those prefixes cannot be aggregated without further configured
policy on the ACP edge node. This explains the above recommendation
to use ACP ULA prefix covered prefixes for ACP connect interfaces:
They allow for a shorter list of prefixes to be signaled via RFC4191
to NMS hosts and software components.
The ACP edge nodes that have a Vlong ACP address MAY allocate a
subset of their /112 or /120 address prefix to ACP connect
interface(s) to eliminate the need to non-autonomically configure/
provision the address prefixes for such ACP connect interfaces.
8.1.4. Combined ACP/Data-Plane Interface (VRF Select)
Combined ACP and Data-Plane interface
.
+--------+ +--------------------+ . +--------------+
| ACP | |ACP Edge No | . | NMS Host(s) |
| Node | | | . | / Software |
| | | [ACP ]. | . | |+
| | | .[VRF ] .[VRF ] | v | "ACP address"||
| +-------+. .[Select].+--------+ "Date Plane ||
| | ^ | .[Data ]. | | Address(es)"||
| | . | [Plane] | | ||
| | . | [ ] | +--------------+|
+--------+ . +--------------------+ +--------------+
.
Data-Plane "native" and + ACP auto-negotiated/encrypted
Figure 17: VRF select
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Using two physical and/or virtual subnets (and therefore interfaces)
into NMS Hosts (as per Section 8.1.1) or Software (as per
Section 8.1.2) may be seen as additional complexity, for example with
legacy NMS Hosts that support only one IP interface, or it may be
insufficient to support [RFC4191] Type A or B host (see
Section 8.1.3).
To provide a single subnet into both ACP and Data-Plane, the ACP Edge
node needs to de-multiplex packets from NMS hosts into ACP VRF and
Data-Plane. This is sometimes called "VRF select". If the ACP VRF
has no overlapping IPv6 addresses with the Data-Plane (it should have
no overlapping addresses), then this function can use the IPv6
Destination address. The problem is Source Address Selection on the
NMS Host(s) according to RFC6724.
Consider the simple case: The ACP uses only one ULA prefix, the ACP
IPv6 prefix for the Combined ACP and Data-Plane interface is covered
by that ULA prefix. The ACP edge node announces both the ACP IPv6
prefix and one (or more) prefixes for the Data-Plane. Without
further policy configurations on the NMS Host(s), it may select its
ACP address as a source address for Data-Plane ULA destinations
because of Rule 8 of RFC6724. The ACP edge node can pass on the
packet to the Data-Plane, but the ACP source address should not be
used for Data-Plane traffic, and return traffic may fail.
If the ACP carries multiple ULA prefixes or non-ULA ACP connect
prefixes, then the correct source address selection becomes even more
problematic.
With separate ACP connect and Data-Plane subnets and RFC4191 prefix
announcements that are to be routed across the ACP connect interface,
RFC6724 source address selection Rule 5 (use address of outgoing
interface) will be used, so that above problems do not occur, even in
more complex cases of multiple ULA and non-ULA prefixes in the ACP
routing table.
To achieve the same behavior with a Combined ACP and Data-Plane
interface, the ACP Edge Node needs to behave as two separate routers
on the interface: One link-local IPv6 address/router for its ACP
reachability, and one link-local IPv6 address/router for its Data-
Plane reachability. The Router Advertisements for both are as
described above (Section 8.1.3): For the ACP, the ACP prefix is
announced together with RFC4191 option for the prefixes routed across
the ACP and lifetime=0 to disqualify this next-hop as a default
router. For the Data-Plane, the Data-Plane prefix(es) are announced
together with whatever dafault router parameters are used for the
Data-Plane.
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In result, RFC6724 source address selection Rule 5.5 may result in
the same correct source address selection behavior of NMS hosts
without further configuration on it as the separate ACP connect and
Data-Plane interfaces. As described in the text for Rule 5.5, this
is only a MAY, because IPv6 hosts are not required to track next-hop
information. If an NMS Host does not do this, then separate ACP
connect and Data-Plane interfaces are the preferable method of
attachment. Hosts implementing [RFC8028] should (instead of may)
implement [RFC6724] Rule 5.5, so it is preferred for hosts to support
[RFC8028].
ACP edge nodes MAY support the Combined ACP and Data-Plane interface.
8.1.5. Use of GRASP
GRASP can and should be possible to use across ACP connect
interfaces, especially in the architectural correct solution when it
is used as a mechanism to connect Software (e.g., ASA or legacy NMS
applications) to the ACP.
Given how the ACP is the security and transport substrate for GRASP,
the requirements for devices connected via ACP connect is that those
are equivalently (if not better) secured against attacks than ACP
nodes that do not use ACP connect and run only software that is
equally (if not better) protected, known (or trusted) not to be
malicious and accordingly designed to isolate access to the ACP
against external equipment.
The difference in security is that cryptographic security of the ACP
secure channel is replaced by required physical security/control of
the network connection between an ACP edge node and the NMS or other
host reachable via the ACP connect interface. See Section 8.1.1.
When using "Combined ACP and Data-Plane Interfaces", care has to be
taken that only GRASP messages intended for the ACP GRASP domain
received from Software or NMS Hosts are forwarded by ACP edge nodes.
Currently there is no definition for a GRASP security and transport
substrate beside the ACP, so there is no definition how such
Software/NMS Host could participate in two separate GRASP Domains
across the same subnet (ACP and Data-Plane domains). At current it
is assumed that all GRASP packets on a Combined ACP and Data-Plane
interface belong to the GRASP ACP Domain. They SHOULD all use the
ACP IPv6 addresses of the Software/NMS Hosts. The link-local IPv6
addresses of Software/NMS Hosts (used for GRASP M_DISCOVERY and
M_FLOOD messages) are also assumed to belong to the ACP address
space.
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8.2. Connecting ACP islands over Non-ACP L3 networks (Remote ACP
neighbors)
Not all nodes in a network may support the ACP. If non-ACP Layer-2
devices are between ACP nodes, the ACP will work across it since it
is IP based. However, the autonomic discovery of ACP neighbors via
DULL GRASP is only intended to work across L2 connections, so it is
not sufficient to autonomically create ACP connections across non-ACP
Layer-3 devices.
8.2.1. Configured Remote ACP neighbor
On the ACP node, remote ACP neighbors are configured explicitly. The
parameters of such a "connection" are described in the following
ABNF.
connection = [ method , local-addr, remote-addr, ?pmtu ]
method = [ "IKEv2", ?port ]
method =/ [ "DTLS", port ]
local-addr = [ address , ?vrf ]
remote-addr = [ address ]
address = ("any" | ipv4-address | ipv6-address )
vrf = tstr ; Name of a VRF on this node with local-address
Figure 18: Parameters for remote ACP neighbors
Explicit configuration of a remote-peer according to this ABNF
provides all the information to build a secure channel without
requiring a tunnel to that peer and running DULL GRASP inside of it.
The configuration includes the parameters otherwise signaled via DULL
GRASP: local address, remote (peer) locator and method. The
differences over DULL GRASP local neighbor discovery and secure
channel creation are as follows:
* The local and remote address can be IPv4 or IPv6 and are typically
global scope addresses.
* The VRF across which the connection is built (and in which local-
addr exists) can to be specified. If vrf is not specified, it is
the default VRF on the node. In DULL GRASP the VRF is implied by
the interface across which DULL GRASP operates.
* If local address is "any", the local address used when initiating
a secure channel connection is decided by source address selection
([RFC6724] for IPv6). As a responder, the connection listens on
all addresses of the node in the selected VRF.
* Configuration of port is only required for methods where no
defaults exist (e.g., "DTLS").
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* If remote address is "any", the connection is only a responder.
It is a "hub" that can be used by multiple remote peers to connect
simultaneously - without having to know or configure their
addresses. Example: Hub site for remote "spoke" sites reachable
over the Internet.
* Pmtu should be configurable to overcome issues/limitations of Path
MTU Discovery (PMTUD).
* IKEv2/IPsec to remote peers should support the optional NAT
Traversal (NAT-T) procedures.
8.2.2. Tunneled Remote ACP Neighbor
An IPinIP, GRE or other form of pre-existing tunnel is configured
between two remote ACP peers and the virtual interfaces representing
the tunnel are configured for "ACP enable". This will enable IPv6
link local addresses and DULL on this tunnel. In result, the tunnel
is used for normal "L2 adjacent" candidate ACP neighbor discovery
with DULL and secure channel setup procedures described in this
document.
Tunneled Remote ACP Neighbor requires two encapsulations: the
configured tunnel and the secure channel inside of that tunnel. This
makes it in general less desirable than Configured Remote ACP
Neighbor. Benefits of tunnels are that it may be easier to implement
because there is no change to the ACP functionality - just running it
over a virtual (tunnel) interface instead of only native interfaces.
The tunnel itself may also provide PMTUD while the secure channel
method may not. Or the tunnel mechanism is permitted/possible
through some firewall while the secure channel method may not.
Tunneling using an insecure tunnel encapsulation increases on average
the risk of a MITM downgrade attack somewhere along the underlay path
that blocks all but the most easily attacked ACP secure channel
option. ACP nodes supporting tunneled remote ACP Neighbors SHOULD
support configuration on such tunnel interfaces to restrict or
explicitly select the available ACP secure channel protocols (if the
ACP node supports more than one ACP secure channel protocol in the
first place).
8.2.3. Summary
Configured/Tunneled Remote ACP neighbors are less "indestructible"
than L2 adjacent ACP neighbors based on link local addressing, since
they depend on more correct Data-Plane operations, such as routing
and global addressing.
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Nevertheless, these options may be crucial to incrementally deploy
the ACP, especially if it is meant to connect islands across the
Internet. Implementations SHOULD support at least Tunneled Remote
ACP Neighbors via GRE tunnels - which is likely the most common
router-to-router tunneling protocol in use today.
9. ACP Operations (Informative)
The following sections document important operational aspects of the
ACP. They are not normative because they do not impact the
interoperability between components of the ACP, but they include
recommendations/requirements for the internal operational model
beneficial or necessary to achieve the desired use-case benefits of
the ACP (see Section 3).
* Section 9.1 describes recommended operator diagnostics
capabilities of ACP nodes.
* Section 9.2 describes high level how an ACP registrar needs to
work, what its configuration parameters are and specific issues
impacting the choices of deployment design due to renewal and
revocation issues. It describes a model where ACP Registrars have
their own sub-CA to provide the most distributed deployment option
for ACP Registrars, and it describes considerations for
centralized policy control of ACP Registrar operations.
* Section 9.3 describes suggested ACP node behavior and operational
interfaces (configuration options) to manage the ACP in so-called
greenfield devices (previously unconfigured) and brownfield
devices (preconfigured).
The recommendations and suggestions of this chapter were derived from
operational experience gained with a commercially available pre-
standard ACP implementation.
9.1. ACP (and BRSKI) Diagnostics
Even though ACP and ANI in general are taking out many manual
configuration mistakes through their automation, it is important to
provide good diagnostics for them.
Basic standardized diagnostics would require support for (yang)
models representing the complete (auto-)configuration and operational
state of all components: GRASP, ACP and the infrastructure used by
them: TLS/DTLS, IPsec, certificates, TA, time, VRF and so on. While
necessary, this is not sufficient:
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Simply representing the state of components does not allow operators
to quickly take action - unless they do understand how to interpret
the data, and that can mean a requirement for deep understanding of
all components and how they interact in the ACP/ANI.
Diagnostic supports should help to quickly answer the questions
operators are expected to ask, such as "is the ACP working
correctly?", or "why is there no ACP connection to a known
neighboring node?"
In current network management approaches, the logic to answer these
questions is most often built as centralized diagnostics software
that leverages the above mentioned data models. While this approach
is feasible for components utilizing the ANI, it is not sufficient to
diagnose the ANI itself:
* Developing the logic to identify common issues requires
operational experience with the components of the ANI. Letting
each management system define its own analysis is inefficient.
* When the ANI is not operating correctly, it may not be possible to
run diagnostics from remote because of missing connectivity. The
ANI should therefore have diagnostic capabilities available
locally on the nodes themselves.
* Certain operations are difficult or impossible to monitor in real-
time, such as initial bootstrap issues in a network location where
no capabilities exist to attach local diagnostics. Therefore, it
is important to also define means of capturing (logging)
diagnostics locally for later retrieval. Ideally, these captures
are also non-volatile so that they can survive extended power-off
conditions - for example when a device that fails to be brought up
zero-touch is being sent back for diagnostics at a more
appropriate location.
The simplest form of diagnostics answering questions such as the
above is to represent the relevant information sequentially in
dependency order, so that the first non-expected/non-operational item
is the most likely root cause. Or just log/highlight that item. For
example:
Q: Is ACP operational to accept neighbor connections:
* Check if any potentially necessary configuration to make ACP/ANI
operational are correct (see Section 9.3 for a discussion of such
commands).
* Does the system time look reasonable, or could it be the default
system time after clock chip battery failure (certificate checks
depend on reasonable notion of time)?.
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* Does the node have keying material - domain certificate, TA
certificates, ...>
* If no keying material and ANI is supported/enabled, check the
state of BRSKI (not detailed in this example).
* Check the validity of the domain certificate:
- Does the certificate validate against the TA?
- Has it been revoked?
- Was the last scheduled attempt to retrieve a CRL successful
(e.g., do we know that our CRL information is up to date).
- Is the certificate valid: validity start time in the past,
expiration time in the future?
- Does the certificate have a correctly formatted acp-node-name
field?
* Was the ACP VRF successfully created?
* Is ACP enabled on one or more interfaces that are up and running?
If all this looks good, the ACP should be running locally "fine" -
but we did not check any ACP neighbor relationships.
Question: why does the node not create a working ACP connection to a
neighbor on an interface?
* Is the interface physically up? Does it have an IPv6 link-local
address?
* Is it enabled for ACP?
* Do we successfully send DULL GRASP messages to the interface (link
layer errors)?
* Do we receive DULL GRASP messages on the interface? If not, some
intervening L2 equipment performing bad MLD snooping could have
caused problems. Provide e.g., diagnostics of the MLD querier
IPv6 and MAC address.
* Do we see the ACP objective in any DULL GRASP message from that
interface? Diagnose the supported secure channel methods.
* Do we know the MAC address of the neighbor with the ACP objective?
If not, diagnose SLAAC/ND state.
* When did we last attempt to build an ACP secure channel to the
neighbor?
* If it failed, why:
- Did the neighbor close the connection on us or did we close the
connection on it because the domain certificate membership
failed?
- If the neighbor closed the connection on us, provide any error
diagnostics from the secure channel protocol.
- If we failed the attempt, display our local reason:
o There was no common secure channel protocol supported by the
two neighbors (this could not happen on nodes supporting
this specification because it mandates common support for
IPsec).
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o The ACP certificate membership check (Section 6.2.3) fails:
+ The neighbor's certificate is not signed directly or
indirectly by one of the nodes TA. Provide diagnostics
which TA it has (can identify whom the device belongs
to).
+ The neighbor's certificate does not have the same domain
(or no domain at all). Diagnose domain-name and
potentially other cert info.
+ The neighbor's certificate has been revoked or could not
be authenticated by OCSP.
+ The neighbor's certificate has expired - or is not yet
valid.
- Any other connection issues in e.g., IKEv2 / IPsec, DTLS?.
Question: Is the ACP operating correctly across its secure channels?
* Are there one or more active ACP neighbors with secure channels?
* Is the RPL routing protocol for the ACP running?
* Is there a default route to the root in the ACP routing table?
* Is there for each direct ACP neighbor not reachable over the ACP
virtual interface to the root a route in the ACP routing table?
* Is ACP GRASP running?
* Is at least one SRV.est objective cached (to support certificate
renewal)?
* Is there at least one BRSKI registrar objective cached (in case
BRSKI is supported)
* Is BRSKI proxy operating normally on all interfaces where ACP is
operating?
* ...
These lists are not necessarily complete, but illustrate the
principle and show that there are variety of issues ranging from
normal operational causes (a neighbor in another ACP domain) over
problems in the credentials management (certificate lifetimes),
explicit security actions (revocation) or unexpected connectivity
issues (intervening L2 equipment).
The items so far are illustrating how the ANI operations can be
diagnosed with passive observation of the operational state of its
components including historic/cached/counted events. This is not
necessary sufficient to provide good enough diagnostics overall:
The components of ACP and BRSKI are designed with security in mind
but they do not attempt to provide diagnostics for building the
network itself. Consider two examples:
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1. BRSKI does not allow for a neighboring device to identify the
pledges IDevID certificate. Only the selected BRSKI registrar
can do this, but it may be difficult to disseminate information
about undesired pledges from those BRSKI registrars to locations/
nodes where information about those pledges is desired.
2. LLDP disseminates information about nodes to their immediate
neighbors, such as node model/type/software and interface name/
number of the connection. This information is often helpful or
even necessary in network diagnostics. It can equally be
considered to be too insecure to make this information available
unprotected to all possible neighbors.
An "interested adjacent party" can always determine the IDevID
certificate of a BRSKI pledge by behaving like a BRSKI proxy/
registrar. Therefore, the IDevID certificate of a BRSKI pledge is
not meant to be protected - it just has to be queried and is not
signaled unsolicited (as it would be in LLDP) so that other observers
on the same subnet can determine who is an "interested adjacent
party".
9.1.1. Secure Channel Peer diagnostics
When using mutual certificate authentication, the TA certificate is
not required to be signaled explicitly because its hash is sufficient
for certificate chain validation. In the case of ACP secure channel
setup this leads to limited diagnostics when authentication fails
because of TA mismatch. For this reason, Section 6.8.2 recommends to
also include the TA certificate in the secure channel signaling.
This should be possible to do without protocol modifications in the
security association protocols used by the ACP. For example, while
[RFC7296] does not mention this, it also does not prohibit it.
One common deployment use case where the diagnostic through the
signaled TA of a candidate peer is very helpful are multi-tenant
environments such as office buildings, where different tenants run
their own networks and ACPs. Each tenant is given supposedly
disjoint L2 connectivity through the building infrastructure. In
these environments there are various common errors through which a
device may receive L2 connectivity into the wrong tenants network.
While the ACP itself is not impact by this, the Data-Plane to be
built later may be impacted. Therefore, it is important to be able
to diagnose such undesirable connectivity from the ACP so that any
autonomic or non-autonomic mechanisms to configure the Data-Plane can
accordingly treat such interfaces. The information in the TA of the
peer can then ease troubleshooting of such issues.
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Another example case is the intended or accidental re-activation of
equipment whose TA certificate has long expired, such as redundant
gear taken from storage after years.
A third example case is when in a mergers & acquisition case ACP
nodes have not been correctly provisioned with the mutual TA of
previously disjoint ACP. This is assuming that the ACP domain names
where already aligned so that the ACP domain membership check is only
failing on the TA.
A fourth example case is when multiple registrars where set up for
the same ACP but without correctly setting up the same TA. For
example, when registrars support to also be CA themselves but are
misconfigured to become TA instead of intermediate CA.
9.2. ACP Registrars
As described in Section 6.11.7, the ACP addressing mechanism is
designed to enable lightweight, distributed and uncoordinated ACP
registrars that are providing ACP address prefixes to candidate ACP
nodes by enrolling them with an ACP certificate into an ACP domain
via any appropriate mechanism/protocol, automated or not.
This section discusses informatively more details and options for ACP
registrars.
9.2.1. Registrar interactions
This section summarizes and discusses the interactions with other
entities required by an ACP registrar.
In a simple instance of an ACP network, no central NOC component
beside a TA is required. Typically, this is a root CA. One or more
uncoordinated acting ACP registrar can be set up, performing the
following interactions:
To orchestrate enrolling a candidate ACP node autonomically, the ACP
registrar can rely on the ACP and use Proxies to reach the candidate
ACP node, therefore allowing minimum pre-existing (auto-)configured
network services on the candidate ACP node. BRSKI defines the BRSKI
proxy, a design that can be adopted for various protocols that
Pledges/candidate ACP nodes could want to use, for example BRSKI over
CoAP (Constrained Application Protocol), or proxying of NETCONF.
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To reach a TA that has no ACP connectivity, the ACP registrar would
use the Data-Plane. ACP and Data-Plane in an ACP registrar could
(and by default should be) completely isolated from each other at the
network level. Only applications such as the ACP registrar would
need the ability for their transport stacks to access both.
In non-autonomic enrollment options, the Data-Plane between a ACP
registrar and the candidate ACP node needs to be configured first.
This includes the ACP registrar and the candidate ACP node. Then any
appropriate set of protocols can be used between ACP registrar and
candidate ACP node to discover the other side, and then connect and
enroll (configure) the candidate ACP node with an ACP certificate.
NETCONF ZeroTouch ([RFC8572]) is an example protocol that could be
used for this. BRSKI using optional discovery mechanisms is equally
a possibility for candidate ACP nodes attempting to be enrolled
across non-ACP networks, such as the Internet.
When candidate ACP nodes have secure bootstrap, such as BRSKI
Pledges, they will not trust to be configured/enrolled across the
network, unless being presented with a voucher (see [RFC8366])
authorizing the network to take possession of the node. An ACP
registrar will then need a method to retrieve such a voucher, either
offline, or online from a MASA (Manufacturer Authorized Signing
Authority). BRSKI and NETCONF ZeroTouch are two protocols that
include capabilities to present the voucher to the candidate ACP
node.
An ACP registrar could operate EST for ACP certificate renewal and/or
act as a CRL Distribution point. A node performing these services
does not need to support performing (initial) enrollment, but it does
require the same above described connectivity as an ACP registrar:
via the ACP to ACP nodes and via the Data-Plane to the TA and other
sources of CRL information.
9.2.2. Registrar Parameter
The interactions of an ACP registrar outlined Section 6.11.7 and
Section 9.2.1 above depend on the following parameters:
* A URL to the TA and credentials so that the ACP registrar can let
the TA sign candidate ACP node certificates.
* The ACP domain-name.
* The Registrar-ID to use. This could default to a MAC address of
the ACP registrar.
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* For recovery, the next-useable Node-IDs for zone (Zone-ID=0) sub-
addressing scheme, for Vlong /112 and for Vlong /120 sub-
addressing scheme. These IDs would only need to be provisioned
after recovering from a crash. Some other mechanism would be
required to remember these IDs in a backup location or to recover
them from the set of currently known ACP nodes.
* Policies if candidate ACP nodes should receive a domain
certificate or not, for example based on the devices IDevID
certificate as in BRSKI. The ACP registrar may have a whitelist
or blacklist of devices [X.520] "serialNumbers" attribute in the
subject field distinguished name encoding from their IDevID
certificate.
* Policies what type of address prefix to assign to a candidate ACP
devices, based on likely the same information.
* For BRSKI or other mechanisms using vouchers: Parameters to
determine how to retrieve vouchers for specific type of secure
bootstrap candidate ACP nodes (such as MASA URLs), unless this
information is automatically learned such as from the IDevID
certificate of candidate ACP nodes (as defined in BRSKI).
9.2.3. Certificate renewal and limitations
When an ACP node renews/rekeys its certificate, it may end up doing
so via a different registrar (e.g., EST server) than the one it
originally received its ACP certificate from, for example because
that original ACP registrar is gone. The ACP registrar through which
the renewal/rekeying is performed would by default trust the acp-
node-name from the ACP nodes current ACP certificate and maintain
this information so that the ACP node maintains its ACP address
prefix. In EST renewal/rekeying, the ACP nodes current ACP
certificate is signaled during the TLS handshake.
This simple scenario has two limitations:
1. The ACP registrars cannot directly assign certificates to nodes
and therefore needs an "online" connection to the TA.
2. Recovery from a compromised ACP registrar is difficult. When an
ACP registrar is compromised, it can insert for example a
conflicting acp-node-name and create thereby an attack against
other ACP nodes through the ACP routing protocol.
Even when such a malicious ACP registrar is detected, resolving the
problem may be difficult because it would require identifying all the
wrong ACP certificates assigned via the ACP registrar after it was
compromised. And without additional centralized tracking of assigned
certificates there is no way to do this.
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9.2.4. ACP Registrars with sub-CA
In situations, where either of the above two limitations are an
issue, ACP registrars could also be sub-CAs. This removes the need
for connectivity to a TA whenever an ACP node is enrolled, and
reduces the need for connectivity of such an ACP registrar to a TA to
only those times when it needs to renew its own certificate. The ACP
registrar would also now use its own (sub-CA) certificate to enroll
and sign the ACP nodes certificates, and therefore it is only
necessary to revoke a compromised ACP registrars sub-CA certificate.
Alternatively one can let it expire and not renew it, when the
certificate of the sub-CA is appropriately short-lived.
As the ACP domain membership check verifies a peer ACP node's ACP
certificate trust chain, it will also verify the signing certificate
which is the compromised/revoked sub-CA certificate. Therefore, ACP
domain membership for an ACP node enrolled from a compromised and
discovered ACP registrar will fail.
ACP nodes enrolled by a compromised ACP registrar would automatically
fail to establish ACP channels and ACP domain certificate renewal via
EST and therefore revert to their role as a candidate ACP members and
attempt to get a new ACP certificate from an ACP registrar - for
example, via BRSKI. In result, ACP registrars that have an
associated sub-CA makes isolating and resolving issues with
compromised registrars easier.
Note that ACP registrars with sub-CA functionality also can control
the lifetime of ACP certificates easier and therefore also be used as
a tool to introduce short lived certificates and not rely on CRL,
whereas the certificates for the sub-CAs themselves could be longer
lived and subject to CRL.
9.2.5. Centralized Policy Control
When using multiple, uncoordinated ACP registrars, several advanced
operations are potentially more complex than with a single, resilient
policy control backend, for example including but not limited to:
* Which candidate ACP node is permitted or not permitted into an ACP
domain. This may not be a decision to be taken upfront, so that a
policy per "serialNumber" attribute in the subject field
distinguished name encoding can be loaded into every ACP
registrar. Instead, it may better be decided in real-time
including potentially a human decision in a NOC.
* Tracking of all enrolled ACP nodes and their certificate
information. For example, in support of revoking individual ACP
nodes certificates.
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* More flexible policies what type of address prefix or even what
specific address prefix to assign to a candidate ACP node.
These and other operations could be introduced more easily by
introducing a centralized Policy Management System (PMS) and
modifying ACP registrar behavior so that it queries the PMS for any
policy decision occurring during the candidate ACP node enrollment
process and/or the ACP node certificate renewal process. For
example, which ACP address prefix to assign. Likewise the ACP
registrar would report any relevant state change information to the
PMS as well, for example when a certificate was successfully enrolled
onto a candidate ACP node.
9.3. Enabling and disabling ACP/ANI
Both ACP and BRSKI require interfaces to be operational enough to
support sending/receiving their packets. In node types where
interfaces are by default (e.g., without operator configuration)
enabled, such as most L2 switches, this would be less of a change in
behavior than in most L3 devices (e.g. routers), where interfaces are
by default disabled. In almost all network devices it is common
though for configuration to change interfaces to a physically
disabled state and that would break the ACP.
In this section, we discuss a suggested operational model to enable/
disable interfaces and nodes for ACP/ANI in a way that minimizes the
risk of operator action to break the ACP in this way, and that also
minimizes operator surprise when ACP/ANI becomes supported in node
software.
9.3.1. Filtering for non-ACP/ANI packets
Whenever this document refers to enabling an interface for ACP (or
BRSKI), it only requires to permit the interface to send/receive
packets necessary to operate ACP (or BRSKI) - but not any other Data-
Plane packets. Unless the Data-Plane is explicitly configured/
enabled, all packets not required for ACP/BRSKI should be filtered on
input and output:
Both BRSKI and ACP require link-local only IPv6 operations on
interfaces and DULL GRASP. IPv6 link-local operations means the
minimum signaling to auto-assign an IPv6 link-local address and talk
to neighbors via their link-local address: SLAAC (Stateless Address
Auto-Configuration - [RFC4862]) and ND (Neighbor Discovery -
[RFC4861]). When the device is a BRSKI pledge, it may also require
TCP/TLS connections to BRSKI proxies on the interface. When the
device has keying material, and the ACP is running, it requires DULL
GRASP packets and packets necessary for the secure-channel mechanism
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it supports, e.g., IKEv2 and IPsec ESP packets or DTLS packets to the
IPv6 link-local address of an ACP neighbor on the interface. It also
requires TCP/TLS packets for its BRSKI proxy functionality, if it
does support BRSKI.
9.3.2. Admin Down State
Interfaces on most network equipment have at least two states: "up"
and "down". These may have product specific names. "down" for
example could be called "shutdown" and "up" could be called "no
shutdown". The "down" state disables all interface operations down
to the physical level. The "up" state enables the interface enough
for all possible L2/L3 services to operate on top of it and it may
also auto-enable some subset of them. More commonly, the operations
of various L2/L3 services is controlled via additional node-wide or
interface level options, but they all become only active when the
interface is not "down". Therefore, an easy way to ensure that all
L2/L3 operations on an interface are inactive is to put the interface
into "down" state. The fact that this also physically shuts down the
interface is in many cases just a side effect, but it may be
important in other cases (see below, Section 9.3.2.2).
One of the common problems of remote management is for the operator
or SDN controller to cut its own connectivity to the remote node by a
configuration impacting its own management connection into the node.
The ACP itself should have no dedicated configuration other than
aforementioned enablement of the ACP on brownfield ACP nodes. This
leaves configuration that cannot distinguish between ACP and Data-
Plane as sources of configuration mistakes as these commands will
impact the ACP even though they should only impact the Data-Plane.
The one ubiquitous type of commands that do this on many type of
routers are interface "down" commands/configurations. When such a
command is applied to the interface through which the ACP provides
access for remote management it would cut the remote management
connection through the ACP because, as outlined above, the "down"
commands typically impact the physical layer too and not only the
Data-Plane services.
To provide ACP/ANI resilience against such operator misconfiguration,
this document recommends to separate the "down" state of interfaces
into an "admin down" state where the physical layer is kept running
and ACP/ANI can use the interface and a "physical down" state. Any
existing "down" configurations would map to "admin down". In "admin
down", any existing L2/L3 services of the Data-Plane should see no
difference to "physical down" state. To ensure that no Data-Plane
packets could be sent/received, packet filtering could be established
automatically as described above in Section 9.3.1.
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An example of non-ACP but ANI traffic that should be permitted to
pass even in "admin-down" state is BRSKI enrollment traffic between
BRSKI pledge and a BRSKI proxy.
As necessary (see discussion below) new configuration options could
be introduced to issue "physical down". The options should be
provided with additional checks to minimize the risk of issuing them
in a way that breaks the ACP without automatic restoration. For
example, they could be denied to be issued from a control connection
(NETCONF/SSH) that goes across the interface itself ("do not
disconnect yourself"). Or they could be performed only temporary and
only be made permanent with additional later reconfirmation.
In the following sub-sections important aspects to the introduction
of "admin down" state are discussed.
9.3.2.1. Security
Interfaces are physically brought down (or left in default down
state) as a form of security. "Admin down" state as described above
provides also a high level of security because it only permits ACP/
ANI operations which are both well secured. Ultimately, it is
subject to security review for the deployment whether "admin down" is
a feasible replacement for "physical down".
The need to trust the security of ACP/ANI operations needs to be
weighed against the operational benefits of permitting this: Consider
the typical example of a CPE (customer premises equipment) with no
on-site network expert. User ports are in physical down state unless
explicitly configured not to be. In a misconfiguration situation,
the uplink connection is incorrectly plugged into such as user port.
The device is disconnected from the network and therefore no
diagnostics from the network side is possible anymore.
Alternatively, all ports default to "admin down". The ACP (but not
the Data-Plane) would still automatically form. Diagnostics from the
network side is possible and operator reaction could include to
either make this port the operational uplink port or to instruct re-
cabling. Security wise, only ACP/ANI could be attacked, all other
functions are filtered on interfaces in "admin down" state.
9.3.2.2. Fast state propagation and Diagnostics
"Physical down" state propagates on many interface types (e.g.,
Ethernet) to the other side. This can trigger fast L2/L3 protocol
reaction on the other side and "admin down" would not have the same
(fast) result.
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Bringing interfaces to "physical down" state is to the best of our
knowledge always a result of operator action, but today, never the
result of autonomic L2/L3 services running on the nodes. Therefore,
one option is to change the operator action to not rely on link-state
propagation anymore. This may not be possible when both sides are
under different operator control, but in that case it is unlikely
that the ACP is running across the link and actually putting the
interface into "physical down" state may still be a good option.
Ideally, fast physical state propagation is replaced by fast software
driven state propagation. For example, a DULL GRASP "admin-state"
objective could be used to auto configure a Bidirectional Forwarding
Protocol (BFD, [RFC5880]) session between the two sides of the link
that would be used to propagate the "up" vs. admin down state.
Triggering physical down state may also be used as a mean of
diagnosing cabling in the absence of easier methods. It is more
complex than automated neighbor diagnostics because it requires
coordinated remote access to both (likely) sides of a link to
determine whether up/down toggling will cause the same reaction on
the remote side.
See Section 9.1 for a discussion about how LLDP and/or diagnostics
via GRASP could be used to provide neighbor diagnostics, and
therefore hopefully eliminating the need for "physical down" for
neighbor diagnostics - as long as both neighbors support ACP/ANI.
9.3.2.3. Low Level Link Diagnostics
"Physical down" is performed to diagnose low-level interface behavior
when higher layer services (e.g., IPv6) are not working. Especially
Ethernet links are subject to a wide variety of possible wrong
configuration/cablings if they do not support automatic selection of
variable parameters such as speed (10/100/1000 Mbps), crossover
(Auto-MDIX) and connector (fiber, copper - when interfaces have
multiple but can only enable one at a time). The need for low level
link diagnostic can therefore be minimized by using fully auto
configuring links.
In addition to "Physical down", low level diagnostics of Ethernet or
other interfaces also involve the creation of other states on
interfaces, such as physical Loopback (internal and/or external) or
bringing down all packet transmissions for reflection/cable-length
measurements. Any of these options would disrupt ACP as well.
In cases where such low-level diagnostics of an operational link is
desired but where the link could be a single point of failure for the
ACP, ASA on both nodes of the link could perform a negotiated
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diagnostic that automatically terminates in a predetermined manner
without dependence on external input ensuring the link will become
operational again.
9.3.2.4. Power Consumption Issues
Power consumption of "physical down" interfaces, may be significantly
lower than those in "admin down" state, for example on long-range
fiber interfaces. Bringing up interfaces, for example to probe
reachability, may also consume additional power. This can make these
type of interfaces inappropriate to operate purely for the ACP when
they are not currently needed for the Data-Plane.
9.3.3. Interface level ACP/ANI enable
The interface level configuration option "ACP enable" enables ACP
operations on an interface, starting with ACP neighbor discovery via
DULL GRAP. The interface level configuration option "ANI enable" on
nodes supporting BRSKI and ACP starts with BRSKI pledge operations
when there is no domain certificate on the node. On ACP/BRSKI nodes,
"ACP enable" may not need to be supported, but only "ANI enable".
Unless overridden by global configuration options (see later), "ACP/
ANI enable" will result in "down" state on an interface to behave as
"admin down".
9.3.4. Which interfaces to auto-enable?
(Section 6.4) requires that "ACP enable" is automatically set on
native interfaces, but not on non-native interfaces (reminder: a
native interface is one that exists without operator configuration
action such as physical interfaces in physical devices).
Ideally, ACP enable is set automatically on all interfaces that
provide access to additional connectivity that allows to reach more
nodes of the ACP domain. The best set of interfaces necessary to
achieve this is not possible to determine automatically. Native
interfaces are the best automatic approximation.
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Consider an ACP domain of ACP nodes transitively connected via native
interfaces. A Data-Plane tunnel between two of these nodes that are
non-adjacent is created and "ACP enable" is set for that tunnel. ACP
RPL sees this tunnel as just as a single hop. Routes in the ACP
would use this hop as an attractive path element to connect regions
adjacent to the tunnel nodes. In result, the actual hop-by-hop paths
used by traffic in the ACP can become worse. In addition, correct
forwarding in the ACP now depends on correct Data-Plane forwarding
config including QoS, filtering and other security on the Data-Plane
path across which this tunnel runs. This is the main issue why "ACP/
ANI enable" should not be set automatically on non-native interfaces.
If the tunnel would connect two previously disjoint ACP regions, then
it likely would be useful for the ACP. A Data-Plane tunnel could
also run across nodes without ACP and provide additional connectivity
for an already connected ACP network. The benefit of this additional
ACP redundancy has to be weighed against the problems of relying on
the Data-Plane. If a tunnel connects two separate ACP regions: how
many tunnels should be created to connect these ACP regions reliably
enough? Between which nodes? These are all standard tunneled
network design questions not specific to the ACP, and there are no
generic fully automated answers.
Instead of automatically setting "ACP enable" on these type of
interfaces, the decision needs to be based on the use purpose of the
non-native interface and "ACP enable" needs to be set in conjunction
with the mechanism through which the non-native interface is created/
configured.
In addition to explicit setting of "ACP/ANI enable", non-native
interfaces also need to support configuration of the ACP RPL cost of
the link - to avoid the problems of attracting too much traffic to
the link as described above.
Even native interfaces may not be able to automatically perform BRSKI
or ACP because they may require additional operator input to become
operational. Example include DSL interfaces requiring PPPoE
credentials or mobile interfaces requiring credentials from a SIM
card. Whatever mechanism is used to provide the necessary config to
the device to enable the interface can also be expanded to decide on
whether or not to set "ACP/ANI enable".
The goal of automatically setting "ACP/ANI enable" on interfaces
(native or not) is to eliminate unnecessary "touches" to the node to
make its operation as much as possible "zero-touch" with respect to
ACP/ANI. If there are "unavoidable touches" such a creating/
configuring a non-native interface or provisioning credentials for a
native interface, then "ACP/ANI enable" should be added as an option
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to that "touch". If a wrong "touch" is easily fixed (not creating
another high-cost touch), then the default should be not to enable
ANI/ACP, and if it is potentially expensive or slow to fix (e.g.,
parameters on SIM card shipped to remote location), then the default
should be to enable ACP/ANI.
9.3.5. Node Level ACP/ANI enable
A node level command "ACP/ANI enable [up-if-only]" enables ACP or ANI
on the node (ANI = ACP + BRSKI). Without this command set, any
interface level "ACP/ANI enable" is ignored. Once set, ACP/ANI will
operate an interface where "ACP/ANI enable" is set. Setting of
interface level "ACP/ANI enable" is either automatic (default) or
explicit through operator action as described in the previous
section.
If the option "up-if-only" is selected, the behavior of "down"
interfaces is unchanged, and ACP/ANI will only operate on interfaces
where "ACP/ANI enable" is set and that are "up". When it is not set,
then "down" state of interfaces with "ACP/ANI enable" is modified to
behave as "admin down".
9.3.5.1. Brownfield nodes
A "brownfield" node is one that already has a configured Data-Plane.
Executing global "ACP/ANI enable [up-if-only]" on each node is the
only command necessary to create an ACP across a network of
brownfield nodes once all the nodes have a domain certificate. When
BRSKI is used ("ANI enable"), provisioning of the certificates only
requires set-up of a single BRSKI registrar node which could also
implement a CA for the network. This is the simplest way to
introduce ACP/ANI into existing (== brownfield) networks.
The need to explicitly enable ACP/ANI is especially important in
brownfield nodes because otherwise software updates may introduce
support for ACP/ANI: Automatic enablement of ACP/ANI in networks
where the operator does not only not want ACP/ANI but where the
operator likely never even heard of it could be quite irritating to
the operator. Especially when "down" behavior is changed to "admin
down".
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Automatically setting "ANI enable" on brownfield nodes where the
operator is unaware of BRSKI and MASA operations could also be an
unlikely but then critical security issue. If an attacker could
impersonate the operator and register as the operator at the MASA or
otherwise get hold of vouchers and can get enough physical access to
the network so pledges would register to an attacking registrar, then
the attacker could gain access to the ACP, and through the ACP gain
access to the Data-Plane.
In networks where the operator explicitly wants to enable the ANI
this could not happen, because the operator would create a BRSKI
registrar that would discover attack attempts, and the operator would
be setting up his registrar with the MASA. Nodes requiring
"ownership vouchers" would not be subject to that attack. See
[I-D.ietf-anima-bootstrapping-keyinfra] for more details. Note that
a global "ACP enable" alone is not subject to these type of attacks,
because it always depends on some other mechanism first to provision
domain certificates into the device.
9.3.5.2. Greenfield nodes
An ACP "greenfield" node is one that does not have any prior
configuration and that can be bootstrapped into the ACP across the
network. To support greenfield nodes, ACP as described in this
document needs to be combined with a bootstrap protocol/mechanism
that will enroll the node with the ACP keying material - ACP
certificate and TA. For ANI nodes, this protocol/mechanism is BRSKI.
When such a node is powered on and determines it is in greenfield
condition, it enables the bootstrap protocol(s)/mechanism(s), and
once the ACP keying material is enrolled, greenfield state ends and
the ACP is started. When BRSKI is used, the node's state reflects
this by setting "ANI enable" upon determination of greenfield state
at power on.
ACP greenfield nodes that in the absence of ACP would have their
interfaces in "down" state SHOULD set all native interfaces into
"admin down" state and only permit Data-Plane traffic required for
the bootstrap protocol/mechanisms.
ACP greenfield state ends either through successful enrolment of ACP
keying material (certificate, TA) or detection of a permitted
termination of ACP greenfield operations.
ACP nodes supporting greenfield operations MAY want to provide
backward compatibility with other forms of configuration/
provisioning, especially when only a subset of nodes are expected to
be deployed with ACP. Such an ACP node SHOULD observe attempts to
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provision/configure the node via interfaces/methods that
traditionally indicate physical possession of the node, such as a
serial or USB console port or a USB memory stick with a bootstrap
configuration. When such an operation is observed before enrollment
of the ACP keying material has completed, the node SHOULD put itself
into the state the node would have been in, if ACP/ANI was disabled
at boot (terminate ACP greenfield operations).
When an ACP greenfield node enables multiple automated ACP or non-ACP
enrollment/bootstrap protocols/mechanisms in parallel, care must be
taken not to terminate any protocol/mechanism before another one has
succeeded to enroll ACP keying material or has progressed to a point
where it is permitted to be a termination reason for ACP greenfield
operations.
Highly secure ACP greenfield nodes may not permit any reason to
terminate ACP greenfield operations, including physical access.
Nodes that claim to support ANI greenfield operations SHOULD NOT
enable in parallel to BRSKI any enrollment/bootstrap protocol/
mechanism that allows Trust On First Use (TOFU, [RFC7435]) over
interfaces other than those traditionally indicating physical
possession of the node. Protocols/mechanisms with published default
username/password authentication are considered to suffer from TOFU.
Securing the bootstrap protocol/mechanism by requiring a voucher
([RFC8366]) can be used to avoid TOFU.
In summary, the goal of ACP greenfield support is to allow remote
automated enrollment of ACP keying materials, and therefore automated
bootstrap into the ACP and to prohibit TOFU during bootstrap with the
likely exception (for backward compatibility) of bootstrapping via
interfaces traditionally indicating physical possession of the node.
9.3.6. Undoing ANI/ACP enable
Disabling ANI/ACP by undoing "ACP/ANI enable" is a risk for the
reliable operations of the ACP if it can be executed by mistake or
unauthorized. This behavior could be influenced through some
additional (future) property in the certificate (e.g., in the acp-
node-name extension field): In an ANI deployment intended for
convenience, disabling it could be allowed without further
constraints. In an ANI deployment considered to be critical more
checks would be required. One very controlled option would be to not
permit these commands unless the domain certificate has been revoked
or is denied renewal. Configuring this option would be a parameter
on the BRSKI registrar(s). As long as the node did not receive a
domain certificate, undoing "ANI/ACP enable" should not have any
additional constraints.
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9.3.7. Summary
Node-wide "ACP/ANI enable [up-if-only]" commands enable the operation
of ACP/ANI. This is only auto-enabled on ANI greenfield devices,
otherwise it must be configured explicitly.
If the option "up-if-only" is not selected, interfaces enabled for
ACP/ANI interpret "down" state as "admin down" and not "physical
down". In "admin-down" all non-ACP/ANI packets are filtered, but the
physical layer is kept running to permit ACP/ANI to operate.
(New) commands that result in physical interruption ("physical down",
"loopback") of ACP/ANI enabled interfaces should be built to protect
continuance or reestablishment of ACP as much as possible.
Interface level "ACP/ANI enable" control per-interface operations.
It is enabled by default on native interfaces and has to be
configured explicitly on other interfaces.
Disabling "ACP/ANI enable" global and per-interface should have
additional checks to minimize undesired breakage of ACP. The degree
of control could be a domain wide parameter in the domain
certificates.
9.4. Partial or Incremental adoption
The ACP Zone Addressing Sub-Scheme (see Section 6.11.3) allows
incremental adoption of the ACP in a network where ACP can be
deployed on edge areas, but not across the core that is connecting
those edges.
In such a setup, each edge network, such as a branch or campus of an
enterprise network has a disjoined ACP to which one or more unique
Zone-IDs are assigned: ACP nodes registered for a specific ACP zone
have to receive ACP Zone Addressing Sub-scheme addresses, for example
by virtue of configuring for each such zone one or more ACP
Registrars with that Zone-ID. All the Registrars for these ACP Zones
need to get ACP certificates from CAs relying on a common set of TA
and of course the same ACP domain name.
These ACP zones can first be brought up as separate networks without
any connection between them and/or they can be connected across a
non-ACP enabled core network through various non-autonomic
operational practices. For example, each separate ACP Zone can have
an edge node that is a layer 3 VPN PE (MPLS or IPv6 layer 3 VPN),
where a complete non-autonomic ACP-Core VPN is created by using the
ACP VRFs and exchanging the routes from those ACP VRFs across the
VPNs non-autonomic routing protocol(s).
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While such a setup is possible with any ACP addressing sub-scheme,
the ACP-Zone Addressing sub-scheme makes it easy to configure and
scalable for any VPN routing protocols because every ACP zone would
only need to indicate one or more /64 ACP Zone Addressing prefix
routes into the ACP-Core VPN as opposed to routes for every
individual ACP node as required in the other ACP addressing schemes.
Note that the non-autonomous ACP-Core VPN would require additional
extensions to propagate GRASP messages when GRASP discovery is
desired across the zones.
For example, one could set up on each Zone edge router a remote ACP
tunnel to a GRASP hub. The GRASP hub could be implemented at the
application level and could run in the NOC of the network. It would
serve to propagate GRASP announcements between ACP Zones and/or
generate GRASP announcements for NOC services.
Such a partial deployment may prove to be sufficient or could evolve
to become more autonomous through future standardized or non-
standardized enhancements, for example by allowing GRASP messages to
be propagated across the layer 3 VPN, leveraging for example L3VPN
Multicast support.
Finally, these partial deployments can be merged into a single
contiguous complete autonomous ACP (given appropriate ACP support
across the core) without changes in the crypto material, because the
node's ACP certificates are from a single ACP.
9.5. Configuration and the ACP (summary)
There is no desirable configuration for the ACP. Instead, all
parameters that need to be configured in support of the ACP are
limitations of the solution, but they are only needed in cases where
not all components are made autonomic. Wherever this is necessary,
it relies on pre-existing mechanisms for configuration such as CLI or
YANG ([RFC7950]) data models.
The most important examples of such configuration include:
* When ACP nodes do not support an autonomic way to receive an ACP
certificate, for example BRSKI, then such certificate needs to be
configured via some pre-existing mechanisms outside the scope of
this specification. Today, router have typically a variety of
mechanisms to do this.
* Certificate maintenance requires PKI functions. Discovery of
these functions across the ACP is automated (see Section 6.2.5),
but their configuration is not.
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* When non-ACP capable nodes such as pre-existing NMS need to be
physically connected to the ACP, the ACP node to which they attach
needs to be configured with ACP-connect according to Section 8.1.
It is also possible to use that single physical connection to
connect both to ACP and the Data-Plane of the network as explained
in Section 8.1.4.
* When devices are not autonomically bootstrapped, explicit
configuration to enable the ACP needs to be applied. See
Section 9.3.
* When the ACP needs to be extended across interfaces other than L2,
the ACP as defined in this document cannot autodiscover candidate
neighbors automatically. Remote neighbors need to be configured,
see Section 8.2.
Once the ACP is operating, any further configuration for the Data-
Plane can be configured more reliably across the ACP itself because
the ACP provides addressing and connectivity (routing) independent of
the Data-Plane itself. For this, the configuration methods simply
need to also allow to operate across the ACP VRF - NETCONF, SSH or
any other method.
The ACP also provides additional security through its hop-by-hop
encryption for any such configuration operations: Some legacy
configuration methods (SNMP, TFTP, HTTP) may not use end-to-end
encryption, and most of the end-to-end secured configuration methods
still allow for easy passive observation along the path about
configuration taking place (transport flows, port numbers, IP
addresses).
The ACP can and should equally be used as the transport to configure
any of the aforementioned non-autonomic components of the ACP, but in
that case, the same caution needs to be exercised as with Data-Plane
configuration without ACP: Misconfiguration may cause the configuring
entity to be disconnected from the node it configures - for example
when incorrectly unconfiguring a remote ACP neighbor through which
the configured ACP node is reached.
10. Summary: Benefits (Informative)
10.1. Self-Healing Properties
The ACP is self-healing:
* New neighbors will automatically join the ACP after successful
validation and will become reachable using their unique ULA
address across the ACP.
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* When any changes happen in the topology, the routing protocol used
in the ACP will automatically adapt to the changes and will
continue to provide reachability to all nodes.
* The ACP tracks the validity of peer certificates and tears down
ACP secure channels when a peer certificate has expired. When
short-lived certificates with lifetimes in the order of OCSP/CRL
refresh times are used, then this allows for removal of invalid
peers (whose certificate was not renewed) at similar speeds as
when using OCSP/CRL. The same benefit can be achieved when using
CRL/OCSP, periodically refreshing the revocation information and
also tearing down ACP secure channels when the peer's (long-lived)
certificate is revoked. There is no requirement against ACP
implementations to require this enhancement though to keep the
mandatory implementations simpler.
The ACP can also sustain network partitions and mergers. Practically
all ACP operations are link local, where a network partition has no
impact. Nodes authenticate each other using the domain certificates
to establish the ACP locally. Addressing inside the ACP remains
unchanged, and the routing protocol inside both parts of the ACP will
lead to two working (although partitioned) ACPs.
There are few central dependencies: A CRL may not be available during
a network partition; a suitable policy to not immediately disconnect
neighbors when no CRL is available can address this issue. Also, an
ACP Registrar or Certification Authority might not be available
during a partition. This may delay renewal of certificates that are
to expire in the future, and it may prevent the enrollment of new
nodes during the partition.
Highly resilient ACP designs can be built by using ACP Registrars
with embedded sub-CA, as outlined in Section 9.2.4. As long as a
partition is left with one or more of such ACP Registrars, it can
continue to enroll new candidate ACP nodes as long as the ACP
Registrar's sub-CA certificate does not expire. Because the ACP
addressing relies on unique Registrar-IDs, a later re-merge of
partitions will also not cause problems with ACP addresses assigned
during partitioning.
After a network partition, a re-merge will just establish the
previous status, certificates can be renewed, the CRL is available,
and new nodes can be enrolled everywhere. Since all nodes use the
same TA, a re-merge will be smooth.
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Merging two networks with different TA requires the ACP nodes to
trust the union of TA. As long as the routing-subdomain hashes are
different, the addressing will not overlap. Accidentally, overlaps
will only happen in the unlikely event of a 40-bit hash collision in
SHA256 (see Section 6.11). Note that the complete mechanisms to
merge networks is out of scope of this specification.
It is also highly desirable for implementation of the ACP to be able
to run it over interfaces that are administratively down. If this is
not feasible, then it might instead be possible to request explicit
operator override upon administrative actions that would
administratively bring down an interface across which the ACP is
running. Especially if bringing down the ACP is known to disconnect
the operator from the node. For example, any such down
administrative action could perform a dependency check to see if the
transport connection across which this action is performed is
affected by the down action (with default RPL routing used, packet
forwarding will be symmetric, so this is actually possible to check).
10.2. Self-Protection Properties
10.2.1. From the outside
As explained in Section 6, the ACP is based on secure channels built
between nodes that have mutually authenticated each other with their
domain certificates. The channels themselves are protected using
standard encryption technologies such as DTLS or IPsec which provide
additional authentication during channel establishment, data
integrity and data confidentiality protection of data inside the ACP
and in addition, provide replay protection.
Attacker will not be able to join the ACP unless they have a valid
ACP certificate. On-path attackers without a valid ACP certificate
cannot inject packets into the ACP due to ACP secure channels. They
can also not decrypt ACP traffic except if they can crack the
encryption. They can attempt behavioral traffic analysis on the
encrypted ACP traffic.
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The degree to which compromised ACP nodes can impact the ACP depends
on the implementation of the ACP nodes and their impairment. When an
attacker has only gained administrative privileges to configure ACP
nodes remotely, the attacker can disrupt the ACP only through one of
the few configuration options to disable it, see Section 9.3, or by
configuring of non-autonomic ACP options if those are supported on
the impaired ACP nodes, see Section 8. Injecting or extracting
traffic into/from an impaired ACP node is only possible when an
impaired ACP node supports ACP connect (see Section 8.1) and the
attacker can control traffic into/from one of the ACP nodes
interfaces, such as by having physical access to the ACP node.
The ACP also serves as protection (through authentication and
encryption) for protocols relevant to OAM that may not have secured
protocol stack options or where implementation or deployment of those
options fail on some vendor/product/customer limitations. This
includes protocols such as SNMP ([RFC3411]), NTP ([RFC5905]), PTP
([IEEE-1588-2008]), DNS ([RFC3596]), DHCPv6 ([RFC3315]), syslog
([RFC3164]), RADIUS ([RFC2865]), Diameter ([RFC6733]), TACACS
([RFC1492]), IPFIX ([RFC7011]), Netflow ([RFC3954]) - just to name a
few. Not all of these protocol references are necessarily the latest
version of protocols but versions that are still widely deployed.
Protection via the ACP secure hop-by-hop channels for these protocols
is meant to be only a stopgap though: The ultimate goal is for these
and other protocols to use end-to-end encryption utilizing the domain
certificate and rely on the ACP secure channels primarily for zero-
touch reliable connectivity, but not primarily for security.
The remaining attack vector would be to attack the underlying ACP
protocols themselves, either via directed attacks or by denial-of-
service attacks. However, as the ACP is built using link-local IPv6
addresses, remote attacks from the Data-Plane are impossible as long
as the Data-Plane has no facilities to remotely send IPv6 link-local
packets. The only exceptions are ACP connected interfaces which
require higher physical protection. The ULA addresses are only
reachable inside the ACP context, therefore, unreachable from the
Data-Plane. Also, the ACP protocols should be implemented to be
attack resistant and not consume unnecessary resources even while
under attack.
10.2.2. From the inside
The security model of the ACP is based on trusting all members of the
group of nodes that receive an ACP certificate for the same domain.
Attacks from the inside by a compromised group member are therefore
the biggest challenge.
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Group members must be protected against attackers so that there is no
easy way to compromise them, or use them as a proxy for attacking
other devices across the ACP. For example, management plane
functions (transport ports) should only be reachable from the ACP but
not the Data-Plane. Especially for those management plane functions
that have no good protection by themselves because they do not have
secure end-to-end transport and to whom ACP not only provides
automatic reliable connectivity but also protection against attacks.
Protection across all potential attack vectors is typically easier to
do in devices whose software is designed from the ground up with ACP
in mind than with legacy software based systems where the ACP is
added on as another feature.
As explained above, traffic across the ACP should still be end-to-end
encrypted whenever possible. This includes traffic such as GRASP,
EST and BRSKI inside the ACP. This minimizes man in the middle
attacks by compromised ACP group members. Such attackers cannot
eavesdrop or modify communications, they can just filter them (which
is unavoidable by any means).
See Appendix A.9.8 for further considerations how to avoid and deal
with compromised nodes.
10.3. The Administrator View
An ACP is self-forming, self-managing and self-protecting, therefore
has minimal dependencies on the administrator of the network.
Specifically, since it is (intended to be) independent of
configuration, there is only limited scope for configuration errors
on the ACP itself. The administrator may have the option to enable
or disable the entire approach, but detailed configuration is not
possible. This means that the ACP must not be reflected in the
running configuration of nodes, except a possible on/off switch (and
even that is undesirable).
While configuration (except for Section 8 and Section 9.2) is not
possible, an administrator must have full visibility of the ACP and
all its parameters, to be able to do trouble-shooting. Therefore, an
ACP must support all show and debug options, as for any other network
function. Specifically, a network management system or controller
must be able to discover the ACP, and monitor its health. This
visibility of ACP operations must clearly be separated from
visibility of Data-Plane so automated systems will never have to deal
with ACP aspects unless they explicitly desire to do so.
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Since an ACP is self-protecting, a node not supporting the ACP, or
without a valid domain certificate cannot connect to it. This means
that by default a traditional controller or network management system
cannot connect to an ACP. See Section 8.1.1 for more details on how
to connect an NMS host into the ACP.
11. Security Considerations
A set of ACP nodes with ACP certificates for the same ACP domain and
with ACP functionality enabled is automatically "self-building": The
ACP is automatically established between neighboring ACP nodes. It
is also "self-protecting": The ACP secure channels are authenticated
and encrypted. No configuration is required for this.
The self-protecting property does not include workarounds for non-
autonomic components as explained in Section 8. See Section 10.2 for
details of how the ACP protects itself against attacks from the
outside and to a more limited degree from the inside as well.
However, the security of the ACP depends on a number of other
factors:
* The usage of domain certificates depends on a valid supporting PKI
infrastructure. If the chain of trust of this PKI infrastructure
is compromised, the security of the ACP is also compromised. This
is typically under the control of the network administrator.
* ACP nodes receive their certificates from ACP registrars. These
ACP registrars are security critical dependencies of the ACP:
Procedures and protocols for ACP registrars are outside the scope
of this specification as explained in Section 6.11.7.1, only
requirements against the resulting ACP certificates are specified.
* Every ACP registrar (for enrollment of ACP certificates) and ACP
EST server (for renewal of ACP certificates) is a security
critical entity and its protocols are security critical protocols.
Both need to be hardened against attacks, similar to a CA and its
protocols. A malicious registrar can enroll malicious nodes to an
ACP network (if the CA delegates this policy to the registrar) or
break ACP routing for example by assigning duplicate ACP address
assignment to ACP nodes via their ACP certificates.
* ACP nodes that are ANI nodes rely on BRSKI as the protocol for ACP
registrars. For ANI type ACP nodes, the security considerations
of BRSKI apply. It enables automated, secure enrollment of ACP
certificates.
* BRSKI and potentially other ACP registrar protocol options require
that nodes have an (X.509v3 based) IDevID. IDevIDs are an option
for ACP registrars to securely identify candidate ACP nodes that
should be enrolled into an ACP domain.
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* For IDevIDs to securely identify the node to which it IDevID is
assigned, the node needs to (1) utilize hardware support such as a
Trusted Platform Module (TPM) to protect against extraction/
cloning of the private key of the IDevID and (2) a hardware/
software infrastructure to prohibit execution of non-authenticated
software to protect against malicious use of the IDevID.
* Like the IDevID, the ACP certificate should equally be protected
from extraction or other abuse by the same ACP node
infrastructure. This infrastructure for IDevID and ACP
certificate is beneficial independent of the ACP registrar
protocol used (BRSKI or other).
* Renewal of ACP certificates requires support for EST, therefore
the security considerations of [RFC7030] related to certificate
renewal/rekeying and TP renewal apply to the ACP. EST security
considerations when using other than mutual certificate
authentication do not apply nor do considerations for initial
enrollment via EST apply, except for ANI type ACP nodes because
BRSKI leverages EST.
* A malicious ACP node could declare itself to be an EST server via
GRASP across the ACP if malicious software could be executed on
it. CA should therefore authenticate only known trustworthy EST
servers, such as nodes with hardware protections against malicious
software. When Registrars use their ACP certificate to
authenticate towards a CA, the id-kp-cmcRA [RFC6402] extended key
usage attribute allows the CA to determine that the ACP node was
permitted during enrollment to act as an ACP registrar. Without
the ability to talk to the CA, a malicious EST server can still
attract ACP nodes attempting to renew their keying material, but
they will fail to perform successful renewal of a valid ACP
certificate. The ACP node attempting to use the malicious EST
server can then continue to use a different EST server, and log a
failure against a malicious EST server.
* Malicious on-path ACP nodes may filter valid EST server
announcements across the ACP, but such malicious ACP nodes could
equally filter any ACP traffic such as the EST traffic itself.
Either attack requires the ability to execute malicious software
on an impaired ACP node though.
* In the absence of malicious software injection, an attacker that
can misconfigure an ACP node which is supporting EST server
functionality could attempt to configure a malicious CA. This
would not result in the ability to successfully renew ACP
certificates, but it could result in DoS attacks by becoming an
EST server and making ACP nodes attempting their ACP certificate
renewal via this impaired ACP node. This problem can be avoided
when the EST server implementation can verify that the CA
configured is indeed providing renewal for certificates of the
node's ACP. The ability to do so depends on the EST-Server to CA
protocol, which is outside the scope of this document.
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In summary, attacks against the PKI/certificate dependencies of the
ACP can be minimized by a variety of hardware/software components
including options such as TPM for IDevID/ACP-certificate,
prohibitions against execution of non-trusted software and design
aspects of the EST Server functionality for the ACP to eliminate
configuration level impairment.
Because ACP peers select one out of potentially more than one
mutually supported ACP secure channel protocols via the approach
described in Section 6.6, ACP secure channel setup is subject to
downgrade attacks by MITM attackers. This can be discovered after
such an attack by additional mechanisms described in Appendix A.9.9.
Alternatively, more advanced channel selection mechanisms can be
devised. [RFC-Editor: Please remove the following sentence]. See
[ACPDRAFT] Appendix B.1. Both options are out of scope of this
document.
The security model of the ACP as defined in this document is tailored
for use with private PKI. The TA of a private PKI provide the
security against maliciously created ACP certificates to give access
to an ACP. Such attacks can create fake ACP certificates with
correct looking AcpNodeNames, but those certificates would not pass
the certificate path validation of the ACP domain membership check
(see Section 6.2.3, point 2).
[RFC-Editor: please remove the following paragraph].
Using public CA is out of scope of this document. See [ACPDRAFT],
Appendix B.3 for further considerations.
There is no prevention of source-address spoofing inside the ACP.
This implies that if an attacker gains access to the ACP, it can
spoof all addresses inside the ACP and fake messages from any other
node. New protocol/services run across the ACP should therefore use
end-to-end authentication inside the ACP. This is already done by
GRASP as specified in this document.
The ACP is designed to enable automation of current network
management and future autonomic peer-to-peer/distributed network
automation. Any ACP member can send ACP IPv6 packet to other ACP
members and announce via ACP GRASP services to all ACP members
without dependency against centralized components.
The ACP relies on peer-to-peer authentication and authorization using
ACP certificates. This security model is necessary to enable the
autonomic ad-hoc any-to-any connectivity between ACP nodes. It
provides infrastructure protection through hop by hop authentication
and encryption - without relying on third parties. For any services
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where this complete autonomic peer-to-peer group security model is
appropriate, the ACP certificate can also be used unchanged. For
example, for any type of Data-Plane routing protocol security.
This ACP security model is designed primarily to protect against
attack from the outside, but not against attacks from the inside. To
protect against spoofing attacks from compromised on-path ACP nodes,
end-to-end encryption inside the ACP is used by new ACP signaling:
GRASP across the ACP using TLS. The same is expected from any non-
legacy services/protocols using the ACP. Because no group-keys are
used, there is no risk for impacted nodes to access end-to-end
encrypted traffic from other ACP nodes.
Attacks from impacted ACP nodes against the ACP are more difficult
than against the Data-Plane because of the autoconfiguration of the
ACP and the absence of configuration options that could be abused
that allow to change/break ACP behavior. This is excluding
configuration for workaround in support of non-autonomic components.
Mitigation against compromised ACP members is possible through
standard automated certificate management mechanisms including
revocation and non-renewal of short-lived certificates. In this
version of the specification, there are no further optimization of
these mechanisms defined for the ACP (but see Appendix A.9.8).
Higher layer service built using ACP certificates should not solely
rely on undifferentiated group security when another model is more
appropriate/more secure. For example, central network configuration
relies on a security model where only few especially trusted nodes
are allowed to configure the Data-Plane of network nodes (CLI,
NETCONF). This can be done through ACP certificates by
differentiating them and introduce roles. See Appendix A.9.5.
Operators and provisioning software developers need to be aware of
how the provisioning/configuration of network devices impacts the
ability of the operator / provisioning software to remotely access
the network nodes. By using the ACP, most of the issues of
configuration/provisioning caused loss of connectivity for remote
provisioning/configuration will be eliminated, see Section 6. Only
few exceptions such as explicit physical interface down configuration
will be left Section 9.3.2.
Many details of ACP are designed with security in mind and discussed
elsewhere in the document:
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IPv6 addresses used by nodes in the ACP are covered as part of the
node's domain certificate as described in Section 6.2.2. This allows
even verification of ownership of a peer's IPv6 address when using a
connection authenticated with the domain certificate.
The ACP acts as a security (and transport) substrate for GRASP inside
the ACP such that GRASP is not only protected by attacks from the
outside, but also by attacks from compromised inside attackers - by
relying not only on hop-by-hop security of ACP secure channels, but
adding end-to-end security for those GRASP messages. See
Section 6.9.2.
ACP provides for secure, resilient zero-touch discovery of EST
servers for certificate renewal. See Section 6.2.5.
ACP provides extensible, auto-configuring hop-by-hop protection of
the ACP infrastructure via the negotiation of hop-by-hop secure
channel protocols. See Section 6.6.
The ACP is designed to minimize attacks from the outside by
minimizing its dependency against any non-ACP (Data-Plane)
operations/configuration on a node. See also Section 6.13.2.
In combination with BRSKI, ACP enables a resilient, fully zero-touch
network solution for short-lived certificates that can be renewed or
re-enrolled even after unintentional expiry (e.g., because of
interrupted connectivity). See Appendix A.2.
Because ACP secure channels can be long lived, but certificates used
may be short lived, secure channels, for example built via IPsec need
to be terminated when peer certificates expire. See Section 6.8.5.
Section 7.2 describes how to implement a routed ACP topology
operating on what effectively is a large bridge-domain when using L3/
L2 routers that operate at L2 in the Data-Plane. In this case, the
ACP is subject to much higher likelihood of attacks by other nodes
"stealing" L2 addresses than in the actual routed case. Especially
when the bridged network includes non-trusted devices such as hosts.
This is a generic issue in L2 LANs. L2/L3 devices often already have
some form of "port security" to prohibit this. They rely on NDP or
DHCP learning of which port/MAC-address and IPv6 address belong
together and block MAC/IPv6 source addresses from wrong ports. This
type of function needs to be enabled to prohibit DoS attacks and
specifically to protect the ACP. Likewise the GRASP DULL instance
needs to ensure that the IPv6 address in the locator-option matches
the source IPv6 address of the DULL GRASP packet.
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12. IANA Considerations
This document defines the "Autonomic Control Plane".
For the ANIMA-ACP-2020 ASN.1 module, IANA is asked to register value
IANA1 for "id-mod-anima-acpnodename-2020" in the "SMI Security for
PKIX Module Identifier" (1.3.6.1.5.5.7.0) registry.
For the otherName / AcpNodeName, IANA is asked to register a value
for IANA2 for id-on-AcpNodeName in the "SMI Security for PKIX Other
Name Forms" (1.3.6.1.5.5.7.8) registry.
The IANA is requested to register the value "AN_ACP" (without quotes)
to the GRASP Objectives Names Table in the GRASP Parameter Registry.
The specification for this value is this document, Section 6.4.
The IANA is requested to register the value "SRV.est" (without
quotes) to the GRASP Objectives Names Table in the GRASP Parameter
Registry. The specification for this value is this document,
Section 6.2.5.
Explanation: This document chooses the initially strange looking
format "SRV.<service-name>" because these objective names would be in
line with potential future simplification of the GRASP objective
registry. Today, every name in the GRASP objective registry needs to
be explicitly allocated with IANA. In the future, this type of
objective names could be considered to be automatically registered in
that registry for the same service for which a <service-nameh> is
registered according to [RFC6335]. This explanation is solely
informational and has no impact on the requested registration.
The IANA is requested to create an ACP Parameter Registry with
currently one registry table - the "ACP Address Type" table.
"ACP Address Type" Table. The value in this table are numeric values
0...3 paired with a name (string). Future values MUST be assigned
using the Standards Action policy defined by [RFC8126]. The
following initial values are assigned by this document:
0: ACP Zone Addressing Sub-Scheme (ACP RFC Section 6.11.3)
1: ACP Vlong Addressing Sub-Scheme (ACP RFC Section 6.11.5) / ACP
Manual Addressing Sub-Scheme (ACP RFC Section 6.11.4)
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13. Acknowledgements
This work originated from an Autonomic Networking project at Cisco
Systems, which started in early 2010. Many people contributed to
this project and the idea of the Autonomic Control Plane, amongst
which (in alphabetical order): Ignas Bagdonas, Parag Bhide, Balaji
BL, Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Michael
Richardson, Ravi Kumar Vadapalli.
Special thanks to Brian Carpenter, Elwyn Davies, Joel Halpern and
Sheng Jiang for their thorough reviews.
Many thanks Ben Kaduk, Roman Danyliv and Eric Rescorla for their
thorough SEC AD reviews, Russ Housley and Erik Kline for their
reviews and to Valery Smyslov, Tero Kivinen, Paul Wouters and Yoav
Nir for review of IPsec and IKEv2 parameters and helping to
understand those and other security protocol details better. Thanks
for Carsten Borman for CBOR/CDDL help.
Further input, review or suggestions were received from: Rene Struik,
Benoit Claise, William Atwood and Yongkang Zhang.
14. Contributors
For all things GRASP including validation code, ongoing document text
support and technical input.
Brian Carpenter
School of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
Email: brian.e.carpenter@gmail.com
For RPL contributions and all things BRSKI/bootstrap including
validation code, ongoing document text support and technical input.
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/mcr/
For the RPL technology choices and text.
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Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
15. Change log [RFC-Editor: Please remove]
This document was developed on https://github.com/anima-wg/autonomic-
control-plane/tree/master/draft-ietf-anima-autonomic-control-plane.
That github repository also contains the document review/reply
emails.
15.1. Summary of changes since entering IESG review
This text replaces the prior changelog with a summary to provide
guidance for further IESG review.
Please see revision -21 for the individual changelogs of prior
versions .
15.1.1. Reviews (while in IESG review status) / status
This document entered IESG review with version -13. It has since
seen the following reviews:
IESG: Original owner/Yes: Terry Manderson (INT).
IESG: No Objection: Deborah Brungard (RTG), Alissa Cooper (GEN),
Warren Kumari (OPS), Mirja Kuehlewind (TSV), Alexey Melnikov (ART),
Adam Roach (ART).
IESG: No Objection, not counted anymore as they have left IESG: Ben
Campbell (ART), Spencer Dawkins (TSV).
IESG: Open DISCUSS hopefully resolved by this version: Eric Rescorla
(SEC, left IESG), Benjamin Kaduk (SEC).
Other: Michael Richardson (WG), Brian Carpenter (WG), Pascal Thubert
(WG), Frank Xialiang (WG), Elwyn Davies (GEN), Joel Halpern (RTGdir),
Yongkang Zhang (WG), William Atwood (WG).
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15.1.2. BRSKI / ACP registrar related enhancements
Only after ACP entered IESG review did it become clear that the in-
progress BRSKI document would not provide all the explanations needed
for ACP registrars as expected earlier by ACP authors. Instead,
BRSKI will only specify a subset of required ACP behavior related to
certificate handling and registrar. There, it became clear that the
ACP draft should specify generic ACP registrar behavior independent
of BRSKI so ACP could be implemented with or without BRSKI and any
manual/proprietary or future standardized BRSKI alternatives (for
example via NETCONF) would understand the requirements for ACP
registrars and its certificate handling.
This lead to additional text about ACP registrars in the ACP
document:
1. Defined relationship ACP / ANI (ANI = ACP + BRSKI).
6.1.4 (new) Overview of TA required for ACP.
6.1.5.5 Added explanations/requirements for Re-enrollment.
6.10.7 Normative requirements for ACP registrars (BRSKI or not).
10.2 Operational expectations against ACP registrars (BRSKI or not).
15.1.3. Normative enhancements since start of IESG review
In addition to above ACP registrar / BRSKI related enhancements there
is a range of minor normative (also explanatory) enhancements since
the start of IESG review:
6.1.1 Hex digits in ACP domain information field now upper-case (no
specific reason except that both options are equally good, but
capitalized ones are used in rfc5234).
6.1.5.3 Added explanations about CRLs.
6.1.5.6 Added explanations of behavior under failing certificates.
6.1.2 Allow ACP address '0' in ACP domain information field: presence
of address indicates permission to build ACP secure channel to node,
0 indicates that the address of the node is assigned by (future)
other means than certificate. Non-autonomic nodes have no address at
all (that was in -13), and can only connect via ACP connect
interfaces to ACP.
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6.1.3 Distinction of real ACP nodes (with address) and those with
domain certificate without address added as a new rule to ACP domain
membership check.
6.6 Added throttling of secure-channel setup attempts.
6.11.1.14 Removed requirement to handle unknown destination ACP
traffic in low-end nodes that would never be RPL roots.
6.12.5 Added recommendation to use IPv6 DAD.
6.1.1, 6.7.1.1, 6.7.2, 6.7.3, 6.8.2 Various refined additional
certificate, secure channel protocol (IPsec/IKEv2 and DTLS) and ACP
GRASP TLS protocol parameter requirements to ensure interoperating
implementations (from SEC-AD review).
15.1.4. Explanatory enhancements since start of IESG review
Beyond the functional enhancements from the previous two sections,
the mayority of changes since -13 are additional explanations from
review feedback, textual nits and restructuring - with no functional
requirement additions/changes.
1.1 Added "applicability and scope" section with summarized
explanations.
2.Added in-band vs. out-of-band management definitions.
6.1.2 (was 6.1.1) expanded explanations of reasoning for elements of
the ACP domain information field.
6.1.3 refined explanations of ACP domain membership check and
justifications for it.
6.5 Elaborated step-by-step secure channel setup.
6.10 Additional explanations for addressing modes, additional table
of addressing formats (thanks MichaelR).
6.10.5 introduced 'F' bit position as a better visual representation
in the Vlong address space.
6.11.1.1 extensive overhaul to improve readability of use of RPL
(from IESG feedback of non-routing/RPL experts).
6.12.2 Added caution about unconfiguring Data-Plane IPv6 addresses
and impact to ACP (limitation of current ACP design, and pointint to
more details in 10.2).
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10.4 New explanations / summary of configurations for ACP (aka: all
config is undesirable and only required for integrating with non-
autonomic components, primarily ACP-connect and Registrars).
11. Textually enhanced / better structured security considerations
section after IESG security review.
A. (new) Moved all explanations and discussions about futures from
section 10 into this new appendix. This text should not be removed
because it captures a lot of repeated asked questions in WG and
during reviews and from users, and also captures ideas for some
likely important followup work. But none of this is relevant to
implementing (section 6) and operating (section 10) the ACP.
15.2. draft-ietf-anima-autonomic-control-plane-30
-29 did pass all IESG DISCUSS. This version cleans up reamining
comments.
Planned to be removed section Appendix A.6 was moved into new
Appendix B.1 to be amended by further A.2, A.3 containing text felt
to be unfit for publication in RFC (see below). Added reference to
this last draft, and referencing those sections ([ACPDRAFT]).
Final discussion with responsible AD (Eric Vyncke): marked all
references to [ACPDRAFT] as to be removed from RFC, as this would be
too unconventional. Likewise also [ACPDRAFT] reference itself.
Added explanation to appendix B.
Comments from Erik Kline:
2. Fine tuned ULA definition.
Comments Michael Richardson / Eric Vyncke.
6.2.4. / 11. Removed text arguing ability how to use public CA (or
not). Replaced with reference to new [ACPDRAFT] section B.3 (not in
RFC) that explains current state of understanding (unfinished).
B.3 New text detailling authors understanding of use of public CA
(will not be in RFC).
Comments/proposals from Ben Kaduk:
Various: Replaced RFC4492 with RFC8422 which is superceeding it.
6.1 Text fix for hash strength 384 bits (from SHA384); Text fix for
ec_point_format extension.
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6.2.1 Text fixup. Removed requirements for ECDH support in
certificate, instead merely explaining the dependencies required IF
this is desired (educational).
6.2.5.4. Fine tuning 2 sentences.
6.3.2. (ACP domain memebership check) Add reference to ACPDRAFT B.2
explaining why ACP domain membership does not validate ACP address of
the connection.
6.4. Downgraded SHOULD to MAY in new -29 suggestion how to deal with
DoS attacks with many GRASP announcements. Will also separately ask
TSV ADs.
6.4. Fixed extension points in CDDL objective-value definitions
(with help from Carsten/Brian).
9.3.5.2. Added explanation when ACP greenfield state ends, and
refined text explaining how to deal with this.
11. removed duplicate paragraph (first, kept paragraph was the fixed
up, improved correct version).
11. Added references to ACPDRAFT B.1, B.2 as possible future
solutions for downgrade attacks.
12. Fixed up text for IANA code point allocation request.
A.6 - removed.
A.9.9 - added one explanatory intro paragraph to makes it easier to
distinguish this option from the B.1 considerations.
B.1 - new text suggested from Ben, replacing A.6 (will not be in
RFC).
B.2 - new text discussing why there is no network layer address
verification in ACP domain membership check (will not be in RFC).
B.4 - Text discussing DULL GRASP attacks via port sweeps and what do
do against it.
Other.
1. Added sentence about FCC outage report from June as example for
in-band management.
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15. added reference to github where document was developed (removed
in RFC, part of changelog).
15.3. draft-ietf-anima-autonomic-control-plane-29
Comments from Robert Wilton:
Improved several textual nits.
Discuss/Comments from Erik Kline:
Editorial suggestions and nits. Thanks!.
6.1.3 Added text about how/why rsub is irrelevant for domain
membership check.
6.3 Added extension points to AN_ACP DULL GRASP objective because for
example ACP domain certificate could be a nice optional additional
parameter and prior syntax would have forced us to encode into
separate objective unnecessarily.
6.7 Using RFC8415 terminology for exponential backoff parameters.
6.11.2 Amended ACP Sub-Addressing table with future code points,
explanations and prefix announced into RPL.
6.12.1.11. Reworked text to better explain how black hole route
works and added expanation for prefix for manual address scheme.
8.1.3. Reworked explanation of RIOs for ACP connect interfaces for
Type C vs. Type A/B hosts.
8.1.4. Added explanation how this "VRF select" option is required
for auto-attachment of Type A/B hosts to ACP and other networks.
Discuss/Comments from Barry Leiba:
Various editorial nits - thanks.
6.1 New section pulling in TLS requirements, no need anymore to
duplicat for ACP GRASP, EST, BRSKI (ACP/ANI nodes) and (if desired)
OCSP/CRLDP. Added rule to start use secure channel only after
negotiation has finished. Added rules not to optimize negotiation
across multiple L2 interfaces to the same peer.
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6.6 Changed role names in secure channel negotiation process: Alice/
Bob -> Decider/Follower. Explanation enhancements. Added definition
for ACP nodes with "0" address.
6.8.3 Improved explanation how IKEv2 forces preference of IPsec over
GRE due to ACP IPsec profiles being Tunneled vs. Transport.
6.8.4 Limited mentioning of DTLS version requirements to this
section.
6.9.2 Removed TLS requirements, they are now in 6.1.
6.10.6 Removed explanation of IANA allocation requirement. Redundant
- already in IANA section, and was seen as confusing.
8.1.1 Clarified that there can be security impacts when weakening
directly connected address RPF filtering for ACP connect interfaces.
Discuss/Comments from Ben Kaduk:
Many good editorial improvements - thanks!.
5. added explanation of what to do upon failed secure channel
establishment.
6.1.1. refined/extended cert public cey crypto algo and better
distinguished algo for the keys of the cert and the key of the
signer.
6.1.1. and following: explicitly defining "serialNumber" to be the
X.520 subject name serialNumber, not the certificate serial Number.
6.1.1. emhasize additional authorization step for EST servers (id-kp-
cmcRA).
6.1.2 changed AcpNodeName ABNF to again use 32HEXDIG instead of self-
defined variation, because authors overlooked that ABNF is case
agnostic (which is fine). Added recommendation to encode as lower
case. Added full ABNF encoding for extensions (any characters as in
"atoms" except the new "+" separator).
6.1.5.3. New text to explain reason for use of HTTPS (instead of
HTTP) for CRLDP and when and how to use HTTPS then.
6.1.5.5. added text explaning why/how and when to maintain TA data
upon failing cert renewal (one version with BRSKI, one version with
other, ess secure bootstrap protocols).
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6.3. new text and requirement about the signaling of transport ports
in DULL GRASP - benefits (no well-known ports required), and problems
(additional DoS attack vector, albeit not worse than pre-existing
ones, depending on setup of L2 subnets.).
6.7.3.1.1. Specified AUTH_HMAC_SHA2_256_128 (as the ESP
authentication algorithm).
6.8.2. Added recommendations for TLS_AES_256_GCM_SHA384,
TLS_CHACHA20_POLY1305_SHA256 when supporting TLS 1.3.
8.2.2. Added explanation about downgrade attack across configured
ACP tunnels and what to do against it.
9.3.5.2. Rewrote most of section as it originally was too centric on
BRSKI. Should now well describe expectations against automated
bootstrap. Introduces new requirement not to call node as in support
of ANI if is ALSO has TOFU bootstrap.
11. Expanded text about malicious EST servers. Added paragraph
about ACP secure channel downgrade attacks. Added paragraphs about
private PKI as a core to allow security against fake certificates,
added paragraph about considerationsproblems when using public PI.
A.10.9 New appendix suggesting how to discover ACP secure channel
negotiation downgrade attacks.
Discuss from Roman Danyliw:
6.1.5.1 - Added requirement to only announce SRV.est when a working
CA connection.
15 - Amended security considerations with text about registrar
dependencies, security of IDevID/ACP-certificate, EST-Server and
GRASP for EST server discovery.
Other:
Conversion to XML v3. Solved empty () taxonomy xref problems.
Various formatting fixes for v3.
Added contributors section.
15.4. draft-ietf-anima-autonomic-control-plane-28
IESG review Roman Danyliw:
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6. Requested additional text elaborating misconfiguration plus
attack vectors.
6.1.3.1 Added paragraph about unsecured NTP as basis for time in the
absence of other options.
6.7.2 reworded text about additional secure channel protocol
reqiurements.
6.7.3.1.2. Added requirement for ACP nodes supporting IKEv2 to
support RFC8247 (not sure how that got dropped from prior versions.
Replaced minimum crypto requirements definition via specific AES
options with more generic "symmetric key/hash strength" requirements.
6.10.7.3. Added example how to derive addressing scheme from IDevID
(PID). Added explanation how to deal with non-persistant registrar
address database (hint: it sucks or is wasteful, what did you
expect).
8.1.1. Added explanation for 'Physical controlled/secured'.
8.1.5. Removed 'Physical controlled/secured' text, refer back to
8.1.1.
8.2.1. Fixed ABNF 'or' syntax line.
9.3.2. Added explanation of remote management problem with interface
"down" type commands.
10.2.1. Added explanations for attacks from impaired ACP nodes.
11. Rewrote intro paragraph. Removed text referring to enrollment/
registrars as they are out of scope of ACP (dependencies only).
11. Added note about need for new protocols inside ACP to use end-
to-end authentication.
11. Rewrote paragraph about operator mistakes so as to be
actionably. Operators must not make mistakes - but ACP minimizes the
mistakes they can make.
ACP domain certificate -> ACP certificate.
Various other cosmetic edits (thanks!) and typo fixes (sorry for not
running full spell check for every version. Will definitely do
before RFC editor).
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Other:
6.12.5.2.1./6.12.5.2.2. Added text explaining link breakage wrt.
RTL (came about re-analyzing behavior after question about hop
count).
Removed now unnecessary references for earlier rrc822Name otherName
choice.
15.5. draft-ietf-anima-autonomic-control-plane-27
Too many revisions with too many fixes. Lets do a one-word change
revision for a change now if it helps to accelerate the review
process.
Added "subjectAltName /" to make it unambiguous that AcpNodeName is
indeed a SAN (from Russ).
15.6. draft-ietf-anima-autonomic-control-plane-26
Russ Housley review of -25.
1.1 Explicit reference for TLS 1.2 RFC.
2. Changed term of "ACP Domain Information" to AcpNodeName (ASN.1) /
acp-node-name (ABNF), also through rest of document.
2. Improved CA behavior definition. changed IDevID/LDevID to IDevID/
LDevID certificate to be more unambiguous.
2. Changed definition of root CA to just refer to how its used in
RFC7030 CA root key update, because thats the only thing relevant to
ACP.
6.1.1 Moved ECDH requirement to end of text as it was not related to
the subject of the initial paragraps. Likewise reference to
CABFORUM.
6.1.1 Reduced cert key requirements to only be MUST for certs with
2048 RSA public key and P-256 curves. Reduced longer keys to SHOULD.
6.1.2 Changed text for conversion from rfc822Name to otherName /
AcpNode, removed all the explanations of benefits coming with
rfc822Name *sob* *sob* *sob*.
6.1.2.1 New ASN.1 definition for otherName / AcpNodeName.
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6.1.3 Fixed up text. re the handling of missing connectivity for
CRLDP / OCSP.
6.1.4 Fixed up text re. inability to use public CA to situation with
otherName / AcpNodeName (no more ACME rfc822Name validation for us
*sob* *sob* *sob*).
12. Added ASN.1 registration requests to IANA section.
Appenices. Minor changes for rfc822Name to otherName change.
Various minor verbal fixes/enhancements.
15.7. draft-ietf-anima-autonomic-control-plane-25
Crypto parameter discuss from Valery Smyslov and Paul Wouters and
resulting changes.
6.7.2 Moved Michael Richardson suggested diagnostic of signaling TA
from IPsec section to this general requirements section and added
explanation how this may be inappropriate if TA payload is considered
secret by TA owner.
6.7.3.1 Added traffic selectors for native IPsec. Improved text
explanation.
6.7.3.1.2 removed misleading text about signaling TA when using
intermediate certs.
6.7.3.1.2 Removed requirement for 'PKCS #7 wrapped X.509 certificate'
requirement on request of Valery Smyslov as it is not defined in
RFC7296 and there are enough options mandated in RFC7296. Replaced
with just informative text to educate readers who are not IPsec
experts what the mandatory option in RFC7296 is that allows to signal
certificates.
6.7.3.1.2 Added SHOULD requirement how to deal with CERTREQ so that
6.7.2 requirement for TA diagnostics will work in IKEv2 (ignoring
CERTREQ is permitted by IKEv2). Added explanation how this will
result in TA cert diagnostics.
6.7.3.1.2 Added requirement for IKEv2 to operate on link-local
addresses for ACP so at to assume ACT cert as the only possible
authenticator - to avoid potentialy failing section from multiple
available certs on a router.
6.7.3.1.2 fixed PKIX- style OID to ASN.1 object AlgorithmIdentifier
(Paul).
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6.7.3.2 Added IPsec traffic selectors for IPsec with GRE.
6.7.5 Added notion that IPsec/GRE MAY be preferred over IPsec/native.
Luckily IPsec/native uses tunneling, whereas IPsec/GRE uses transport
mode, and there is a long discuss whether it is permitted to even
build IPsec connectings that only support transports instead of
always being able to fall back to tunnel mode. Added explanatory
paragraph why ACP nodes may prefer GRE over native (wonder how that
was missing..).
9.1.1 Added section to explain need for secure channel peer
diagnostics via signaling of TA. Four examples given.
Paul Wouters mentioned that ipkcs7 had to be used in some interop
cases with windows CA, but that is an issue of ACP Registrar having
to convert into PKCS#7 to talk to a windows CA, and this spec is not
concerned with that, except to know that it is feasible, so not
mentioned in text anywhere, just tracking discussion here in
changelog.
Michael Richardson:
3.1.3 Added point in support of rfc822address that CA may not support
to sign certificates with new attributes (such as new otherName).
Michael Richardson/Brian Carpenter fix:
6.1.5.1/6.3 Fixed GRASP examples.
Joe Halpern review:
1. Enhanded introduction text for in-band and of out-of-band,
explaining how ACP is an in-band network aiming to achieve all
possible benefits of an out-of-band network.
1. Comprehensive explanation for term Data-Plane as it is only
logically following pre-established terminology on a fully autonomic
node, when used for existing nodes augmented with ACP, Data-Plane has
more functionality than usually associated with the term.
2. Removed explanatory text for Data-Plane, referring to section 1.
2. Reduced explanation in definition of in-band (management/
signaling), out-of-band-signaling, now pointing to section 1.
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5. Rewrote a lot of the steps (overview) as this text was not
reviewed for long time. Added references to normative section for
each step to hopefully avoid feedback of not explaining terms used
(really not possible to give good summary without using forward
references).
2. Separate out-of-band-management definition from virtual out-of-
band-management definition (later one for ACP).
2. Added definitions for RPI and RPL.
6.1.1. added note about end-to-end authentication to distinguish
channel security from overall ACP security model.
6.5 Fixed bugs in channel selection signaling step description (Alice
vs. Bob).
6.7.1 Removed redundant channel selection explanation.
6.10.3 remove locator/identifier terminology from zone addressing
scheme description (unnecessary), removed explanations (now in 9.4),
simplified text, clarified requirement for Node-ID to be unique,
recommend to use primarily zone 0.
6.10.3.1 Removed. Included a lot of insufficient suggestions for
future stanards extensions, most of it was wrong or would need to be
revisited by WG anyhow. Idea now (just here for comment): Announce
via GRASP Zone-ID (e.g. from per-zone edge-node/registrar) into a
zone of the ACP so all nodes supporting the scheme can automatically
self-allocate the Zone-ID.
6.11.1.1 (RPL overview), eliminated redundant text.
6.11.1.1.1 New subsection to better structure overview.
6.11.1.1.2 New subsection to better group overview, replaced TTL
explanation (just the symptom) with hopefully better reconvergence
text (intent of the profile) for the ACP RPL profile.
6.11.1.1.6 Added text to explain simple choice for rank_factor.
6.11.1.13 moved explanation for RPI up into 6.11.1.1.
6.12.5.1 rewrote section for ACP Loopback Interface.
9.4 New informative/informational section for partial or incremental
adoption of ACP to help understand why there is the Zone interface
sub-scheme, and how to use it.
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Unrelated fixes:
Ask to RFC editor to add most important abbreviations to RFC editor
abbreviation list.
6.10.2 changed names in ACP addressing scheme table to be less
suggestive of use.
Russ Hously review:
2. Fixed definition of "Enrollment", "Trust Anchor", "CA", and "root
CA". Changed "Certificate Authority" to "Certification Authority"
throughout the document (correct term according to X.509).
6.1 Fixed explanation of mutual ACP trust.
6.1.1 s/X509/X509v3/.
6.1.2 created bulleted lists for explanations and justifications for
choices of ACP certificate encoding. No semantic changes, just to
make it easier to refer to the points in discussions (rfcdiff seems
to have a bug showing text differences due to formatting changes).
6.1.3 Moved content of rule #1 into previous rule #2 because
certification chain validation does imply validation of lifetime.
numbers of all rules reduced by 1, changed hopefully all references
to the rule numbers in the document.
Rule #3, Hopefully fixed linguistic problem self-contradiction of
MUST by lower casing MUST in the explanation part and rewriting the
condition when this is not applicable.
6.1.4 Replaced redundant term "Trust Point" (TP) with Trust Anchor
(TA"). Replaced throughout document Trust Anchor with abbreviation
TA.
Enhanced several sentences/rewrote paragraphs to make explanations
clearer.
6.6 Added explanation how ACP nodes must throttle their attempts for
connection making purely on the result of their own connection
attempts, not based on those connections where they are responder.
15.8. draft-ietf-anima-autonomic-control-plane-24
Leftover from -23 review by Eric Vyncke:
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Swapping sections 9 and 10, section 9 was meant to be at end of
document and summarize. Its not meant to be misinterpreted as
introducing any new information. This did happen because section 10
was added after section 9.
15.9. draft-ietf-anima-autonomic-control-plane-23
Note: big rfcdiff of TOC is an rfcdiff bug, changes really minimal.
Review of IPsec security with Mcr and ipsec mailing list.
6.7.1 - new section: Moved general considerations for secure channel
protocols here, refined them.
6.7.2 - new section: Moved common requirements for secure channel
protocols here, refined them.
6.7.3.1.1. - improved requirements text related to RFC8221, better
explamations re. HW acceleration issues.
6.7.3.1.2. - improved requirements text related to RFC8247, (some
requirements still discussed to be redundant, will be finalized in
next weeks.
Eric Vyncke review of -21:
Only noting most important changes, long list of smaller text/
readability enhancements.
2. - New explanation of "normative", "informational" section title
tags. alphabetic reordering of terms, refined definitions for CA,
CRL. root CA.
6.1.1. - explanation when IDevID parameters may be copied into
LDevID.
6.1.2. - Fixed hex digits in ACP domain information to lower case.
6.1.3.1. - New section on Realtime clock and Time Validation.
6.3 - Added explanation that DTLS means >= version 1.2 (not only
1.2).
6.7 - New text in this main section explaing relationship of ACP
secure channels and ACP virtual interfaces - with forward references
to virtual interface section.
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6.8.2 - reordered text and picture, no text change.
6.10.7.2 - describe first how Registrar-ID can be allocted for all
type of registrars, then refined text for how to potentially use MAC
addresses on physical registrars.
6.11.1.1 - Added text how this profile does not use Data-Plane
artefacts (RPI) because hadware forwarding. This was previously
hidden only later in the text.
6.11.1.13. - Rewrote RPL Data-Plane artefact text. Provide decoder
ring for abbreviations and all relevant RFCs.
6.12.5.2. - Added more explicit text that secure channels are mapped
into virtual interfaces, moved different type of interfaces used by
ACP into separate subsections to be able to refer to them.
7.2 - Rewrote/refined text for ACP on L2, prior text was confusing
and did not well explain why ACP for L2/L3 switches can be
implemented without any L2 (HW) changes. Also missing explanation of
only running GRASP untagged when VLANs are used.
8.1.1 - Added requirement for ACP Edge nodes to allow configurable
filtering of IPv6 RPI headers.
11. - (security section). Moved explanation of address stealing from
7.2 to here.
15.10. draft-ietf-anima-autonomic-control-plane-22
Ben Kaduk review of -21:
RFC822 encoding of ACP domain information:
6.1.2 rewrote text for explaining / justifying use of rfc822name as
identifier for node CP in certificate (was discussed in thread, but
badly written in prior versions).
6.1.2 Changed EBNF syntax to use "+" after rfcSELF because that is
the known primary name to extensions separator in many email systems
("." was wrong in prior versions).
6.1.2 Rewrote/improved explanations for use of rfc822name field to
explain better why it is PKIX compliant and the right thing to do.
Crypto parameters for IPsec:
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6.1 - Added explanation of why manual keying for ACP is not feasible
for ACP. Surprisingly, that text did not exist. Referred to by
IPsec text (6.7.1), but here is the right place to describe the
reasoning.
6.1.2 - Small textual refinement referring to requirements to
authenticate peers (for the special cases of empty or '0' ACP address
in ACP domain information field.
6.3 - To better justify Bens proposed change of secure channel
protocol being IPsec vs. GRASP objective being IKEv2, better
explained how protocol indicated in GRASP objective-value is name of
protocol used to negotiate secure channel, use example of IKEv2 to
negotiate IPsec.
6.7.1 - refinemenet similar to 6.3.
- moved new paragraph from Bens pull request up from 6.7.1.1 to 6.7.1
as it equally applies to GRE encapped IPsec (looks nicer one level
up).
- created subsections 6.7.1.1 (IPsec/ESP) / 6.7.1.2 (IKEv2) to
clearer distinguish between these two requirements blocks.
- Refined the text in these two sections to hopefully be a good
answer to Valery's concern of not randomnly mocking with existing
requirements docs (rfc8247 / rfc8221).
6.7.1.1.1 - IPsec/ESP requirements section:
- MUST support rfc8221 mandatory EXCEPT for the superceeding
requirements in this section. Previously, this was not quite clear
from the text.
- Hopefully persuasive explanations about the requirements levels for
ENCR_AES_GCM_16, ENCR_AES_CBC, ENCR_AES_CCM_8 and
ENCR_CHACHA20_POLY1305: Restructured text for why not ENCR_AES_CBC
(was in prior version, just not well structured), added new
expanations for ENCR_AES_CCM_8 and ENCR_CHACHA20_POLY130.
- In simple terms, requirements for ENCR_AES_CBC, ENCR_AES_CCM_8,
ENCR_CHACHACHA are SHOULD when they are implementable with rqual or
faster performancce than ENCR_AES_GCM_16.
- Removed text about "additional rfc8221" reqiurements MAY be used.
Now the logic is that all other requirements apply. Hopefully we
have written enough so that we prohibited downgrades.
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6.7.1.1.2 - RFC8247 requirements:
- Added mandate to support rfc8247, added explanation that there is
no "stripping down" requirement, just additional stronger
requirements to mandate correct use of ACP certificartes during
authentication.
- refined text on identifying ACP by IPv6 address to be clearer:
Identifying in the context of IKEv2 and cases for '0' in ACP domain
information.
- removed last two paragraphs about relationship to rfc8247, as his
is now written in first paragraph of the section.
End of Ben Kaduk review related fixes.
Other:
Forgot to update example of ACP domain information to use capitalized
hex-digits as required by HEXDIG used.
Added reference to RFC8316 (AN use-cases) to beginning of section 3
(ACP use cases).
Small Enhanced IPsec parameters description / requirements fixes
(from Michael Richardson).
16. Normative References
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", Work in Progress, Internet-
Draft, draft-ietf-anima-bootstrapping-keyinfra-43, 7
August 2020, <http://www.ietf.org/internet-drafts/draft-
ietf-anima-bootstrapping-keyinfra-43.txt>.
[I-D.ietf-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", Work in Progress,
Internet-Draft, draft-ietf-anima-grasp-15, 13 July 2017,
<http://www.ietf.org/internet-drafts/draft-ietf-anima-
grasp-15.txt>.
[IKEV2IANA]
IANA, "Internet Key Exchange Version 2 (IKEv2)
Parameters", <https://www.iana.org/assignments/ikev2-
parameters/ikev2-parameters.xhtml>.
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[RFC1034] Mockapetris, P.V., "Domain names - concepts and
facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034,
November 1987, <https://www.rfc-editor.org/info/rfc1034>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
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[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<https://www.rfc-editor.org/info/rfc6551>.
[RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing
Protocol for Low-Power and Lossy Networks (RPL)",
RFC 6552, DOI 10.17487/RFC6552, March 2012,
<https://www.rfc-editor.org/info/rfc6552>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
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[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7676] Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
for Generic Routing Encapsulation (GRE)", RFC 7676,
DOI 10.17487/RFC7676, October 2015,
<https://www.rfc-editor.org/info/rfc7676>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8221] Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
Kivinen, "Cryptographic Algorithm Implementation
Requirements and Usage Guidance for Encapsulating Security
Payload (ESP) and Authentication Header (AH)", RFC 8221,
DOI 10.17487/RFC8221, October 2017,
<https://www.rfc-editor.org/info/rfc8221>.
[RFC8247] Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
"Algorithm Implementation Requirements and Usage Guidance
for the Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 8247, DOI 10.17487/RFC8247, September 2017,
<https://www.rfc-editor.org/info/rfc8247>.
[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
Curve Cryptography (ECC) Cipher Suites for Transport Layer
Security (TLS) Versions 1.2 and Earlier", RFC 8422,
DOI 10.17487/RFC8422, August 2018,
<https://www.rfc-editor.org/info/rfc8422>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
17. Informative References
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[ACPDRAFT] Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
Control Plane (ACP)", Work in Progress, Internet-Draft,
draft-ietf-anima-autonomic-control-plane-30,
<https://tools.ietf.org/html/draft-ietf-anima-autonomic-
control-plane-30.pdf>. [RFC-Editor: Please remove this
complete reference from the RFC] Refer to the IETF working
group draft for the few sections removed from this
document for various reasons. They capture the state of
discussion about unresolved issues that may need to be
revisited in future work.
[AR8021] Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
metropolitan area networks - Secure Device Identity",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[CABFORUM] CA/Browser Forum, "Certificate Contents for Baseline SSL",
November 2019, <https://cabforum.org/baseline-
requirements-certificate-contents/>.
[FCC] FCC, "FCC STAFF REPORT ON NATIONWIDE T-MOBILE NETWORK
OUTAGE ON JUNE 15, 2020 (PS Docket No. 20-183)", 2020,
<https://docs.fcc.gov/public/attachments/DOC-
367699A1.docx>. The FCC's Public Safety and Homeland
Security Bureau issues a report on a nationwide T-Mobile
outage that occurred on June 15, 2020. Action by: Public
Safety and Homeland Security Bureau.
[I-D.eckert-anima-noc-autoconfig]
Eckert, T., "Autoconfiguration of NOC services in ACP
networks via GRASP", Work in Progress, Internet-Draft,
draft-eckert-anima-noc-autoconfig-00, 2 July 2018,
<http://www.ietf.org/internet-drafts/draft-eckert-anima-
noc-autoconfig-00.txt>.
[I-D.ietf-acme-star]
Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
Fossati, "Support for Short-Term, Automatically-Renewed
(STAR) Certificates in Automated Certificate Management
Environment (ACME)", Work in Progress, Internet-Draft,
draft-ietf-acme-star-11, 24 October 2019,
<http://www.ietf.org/internet-drafts/draft-ietf-acme-star-
11.txt>.
[I-D.ietf-anima-prefix-management]
Jiang, S., Du, Z., Carpenter, B., and Q. Sun, "Autonomic
IPv6 Edge Prefix Management in Large-scale Networks", Work
in Progress, Internet-Draft, draft-ietf-anima-prefix-
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management-07, 18 December 2017, <http://www.ietf.org/
internet-drafts/draft-ietf-anima-prefix-management-
07.txt>.
[I-D.ietf-anima-reference-model]
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
and J. Nobre, "A Reference Model for Autonomic
Networking", Work in Progress, Internet-Draft, draft-ietf-
anima-reference-model-10, 22 November 2018,
<http://www.ietf.org/internet-drafts/draft-ietf-anima-
reference-model-10.txt>.
[I-D.ietf-roll-applicability-template]
Richardson, M., "ROLL Applicability Statement Template",
Work in Progress, Internet-Draft, draft-ietf-roll-
applicability-template-09, 3 May 2016,
<http://www.ietf.org/internet-drafts/draft-ietf-roll-
applicability-template-09.txt>.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-38, 29 May 2020, <http://www.ietf.org/internet-
drafts/draft-ietf-tls-dtls13-38.txt>.
[IEEE-1588-2008]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
December 2008, <http://standards.ieee.org/findstds/
standard/1588-2008.html>.
[IEEE-802.1X]
Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
Metropolitan Area Networks: Port-Based Network Access
Control", February 2010,
<http://standards.ieee.org/findstds/standard/802.1X-
2010.html>.
[LLDP] Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
Metropolitan Area Networks: Station and Media Access
Control Connectivity Discovery", June 2016,
<https://standards.ieee.org/findstds/standard/802.1AB-
2016.html>.
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[MACSEC] Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
Metropolitan Area Networks: Media Access Control (MAC)
Security", June 2006,
<https://standards.ieee.org/findstds/standard/802.1AE-
2006.html>.
[RFC1112] Deering, S.E., "Host extensions for IP multicasting",
STD 5, RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[RFC1492] Finseth, C., "An Access Control Protocol, Sometimes Called
TACACS", RFC 1492, DOI 10.17487/RFC1492, July 1993,
<https://www.rfc-editor.org/info/rfc1492>.
[RFC1654] Rekhter, Y., Ed. and T. Li, Ed., "A Border Gateway
Protocol 4 (BGP-4)", RFC 1654, DOI 10.17487/RFC1654, July
1994, <https://www.rfc-editor.org/info/rfc1654>.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998,
<https://www.rfc-editor.org/info/rfc2315>.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
<https://www.rfc-editor.org/info/rfc2409>.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, DOI 10.17487/RFC2865, June 2000,
<https://www.rfc-editor.org/info/rfc2865>.
[RFC3164] Lonvick, C., "The BSD Syslog Protocol", RFC 3164,
DOI 10.17487/RFC3164, August 2001,
<https://www.rfc-editor.org/info/rfc3164>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
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[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<https://www.rfc-editor.org/info/rfc3411>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/info/rfc3596>.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, DOI 10.17487/RFC3920,
October 2004, <https://www.rfc-editor.org/info/rfc3920>.
[RFC3954] Claise, B., Ed., "Cisco Systems NetFlow Services Export
Version 9", RFC 3954, DOI 10.17487/RFC3954, October 2004,
<https://www.rfc-editor.org/info/rfc3954>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/info/rfc4210>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
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[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
August 2006, <https://www.rfc-editor.org/info/rfc4604>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
[RFC4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610,
DOI 10.17487/RFC4610, August 2006,
<https://www.rfc-editor.org/info/rfc4610>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure
Subject Alternative Name for Expression of Service Name",
RFC 4985, DOI 10.17487/RFC4985, August 2007,
<https://www.rfc-editor.org/info/rfc4985>.
[RFC5790] Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
DOI 10.17487/RFC5790, February 2010,
<https://www.rfc-editor.org/info/rfc5790>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/info/rfc5912>.
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[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
[RFC6402] Schaad, J., "Certificate Management over CMS (CMC)
Updates", RFC 6402, DOI 10.17487/RFC6402, November 2011,
<https://www.rfc-editor.org/info/rfc6402>.
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
October 2011, <https://www.rfc-editor.org/info/rfc6407>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<https://www.rfc-editor.org/info/rfc6733>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/info/rfc6824>.
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[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7404] Behringer, M. and E. Vyncke, "Using Only Link-Local
Addressing inside an IPv6 Network", RFC 7404,
DOI 10.17487/RFC7404, November 2014,
<https://www.rfc-editor.org/info/rfc7404>.
[RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
Defined Networking (SDN): Layers and Architecture
Terminology", RFC 7426, DOI 10.17487/RFC7426, January
2015, <https://www.rfc-editor.org/info/rfc7426>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<https://www.rfc-editor.org/info/rfc7575>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<https://www.rfc-editor.org/info/rfc7576>.
[RFC7585] Winter, S. and M. McCauley, "Dynamic Peer Discovery for
RADIUS/TLS and RADIUS/DTLS Based on the Network Access
Identifier (NAI)", RFC 7585, DOI 10.17487/RFC7585, October
2015, <https://www.rfc-editor.org/info/rfc7585>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
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[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8316] Nobre, J., Granville, L., Clemm, A., and A. Gonzalez
Prieto, "Autonomic Networking Use Case for Distributed
Detection of Service Level Agreement (SLA) Violations",
RFC 8316, DOI 10.17487/RFC8316, February 2018,
<https://www.rfc-editor.org/info/rfc8316>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<https://www.rfc-editor.org/info/rfc8368>.
[RFC8398] Melnikov, A., Ed. and W. Chuang, Ed., "Internationalized
Email Addresses in X.509 Certificates", RFC 8398,
DOI 10.17487/RFC8398, May 2018,
<https://www.rfc-editor.org/info/rfc8398>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
[X.509] International Telecommunication Union, "Information
technology - Open Systems Interconnection - The Directory:
Public-key and attribute certificate frameworks", ITU-T
Recommendation X.509, ISO/IEC 9594-8, October 2016,
<https://www.itu.int/rec/T-REC-X.509>.
[X.520] International Telecommunication Union, "Information
technology - Open Systems Interconnection - The Directory:
Selected attribute types", ITU-T Recommendation
X.520, ISO/IEC 9594-6, October 2016,
<https://www.itu.int/rec/T-REC-X.520>.
Appendix A. Background and Futures (Informative)
The following sections discuss additional background information
about aspects of the normative parts of this document or associated
mechanisms such as BRSKI (such as why specific choices were made by
the ACP) and they provide discussion about possible future variations
of the ACP.
A.1. ACP Address Space Schemes
This document defines the Zone, Vlong and Manual sub address schemes
primarily to support address prefix assignment via distributed,
potentially uncoordinated ACP registrars as defined in
Section 6.11.7. This costs 48/46-bit identifier so that these ACP
registrar can assign non-conflicting address prefixes. This design
does not leave enough bits to simultaneously support a large number
of nodes (Node-ID) plus a large prefix of local addresses for every
node plus a large enough set of bits to identify a routing Zone. In
result, Zone, Vlong 8/16 attempt to support all features, but via
separate prefixes.
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In networks that always expect to rely on a centralized PMS as
described above (Section 9.2.5), the 48/46-bits for the Registrar-ID
could be saved. Such variations of the ACP addressing mechanisms
could be introduced through future work in different ways. If a new
otherName was introduced, incompatible ACP variations could be
created where every design aspect of the ACP could be changed.
Including all addressing choices. If instead a new addressing sub-
type would be defined, it could be a backward compatible extension of
this ACP specification. Information such as the size of a zone-
prefix and the length of the prefix assigned to the ACP node itself
could be encoded via the extension field of the acp-node-name.
Note that an explicitly defined "Manual" addressing sub-scheme is
always beneficial to provide an easy way for ACP nodes to prohibit
incorrect manual configuration of any non-"Manual" ACP address spaces
and therefore ensure that "Manual" operations will never impact
correct routing for any non-"Manual" ACP addresses assigned via ACP
certificates.
A.2. BRSKI Bootstrap (ANI)
BRSKI describes how nodes with an IDevID certificate can securely and
zero-touch enroll with an LDevID certificate to support the ACP.
BRSKI also leverages the ACP to enable zero-touch bootstrap of new
nodes across networks without any configuration requirements across
the transit nodes (e.g., no DHCP/DNS forwarding/server setup). This
includes otherwise not configured networks as described in
Section 3.2. Therefore, BRSKI in conjunction with ACP provides for a
secure and zero-touch management solution for complete networks.
Nodes supporting such an infrastructure (BRSKI and ACP) are called
ANI nodes (Autonomic Networking Infrastructure), see
[I-D.ietf-anima-reference-model]. Nodes that do not support an
IDevID certificate but only an (insecure) vendor specific Unique
Device Identifier (UDI) or nodes whose manufacturer does not support
a MASA could use some future security reduced version of BRSKI.
When BRSKI is used to provision a domain certificate (which is called
enrollment), the BRSKI registrar (acting as an enhanced EST server)
must include the otherName / AcpNodeName encoded ACP address and
domain name to the enrolling node (called pledge) via its response to
the pledges EST CSR Attribute request that is mandatory in BRSKI.
The Certification Authority in an ACP network must not change the
otherName / AcpNodeName in the certificate. The ACP nodes can
therefore find their ACP address and domain using this field in the
domain certificate, both for themselves, as well as for other nodes.
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The use of BRSKI in conjunction with the ACP can also help to further
simplify maintenance and renewal of domain certificates. Instead of
relying on CRL, the lifetime of certificates can be made extremely
small, for example in the order of hours. When a node fails to
connect to the ACP within its certificate lifetime, it cannot connect
to the ACP to renew its certificate across it (using just EST), but
it can still renew its certificate as an "enrolled/expired pledge"
via the BRSKI bootstrap proxy. This requires only that the BRSKI
registrar honors expired domain certificates and that the pledge
attempts to perform TLS authentication for BRSKI bootstrap using its
expired domain certificate before falling back to attempting to use
its IDevID certificate for BRSKI. This mechanism could also render
CRLs unnecessary because the BRSKI registrar in conjunction with the
CA would not renew revoked certificates - only a "Do-not-renew" list
would be necessary on BRSKI registrars/CA.
In the absence of BRSKI or less secure variants thereof, provisioning
of certificates may involve one or more touches or non-standardized
automation. Node vendors usually support provisioning of
certificates into nodes via PKCS#7 (see [RFC2315]) and may support
this provisioning through vendor specific models via NETCONF
([RFC6241]). If such nodes also support NETCONF Zero-Touch
([RFC8572]) then this can be combined to zero-touch provisioning of
domain certificates into nodes. Unless there are equivalent
integration of NETCONF connections across the ACP as there is in
BRSKI, this combination would not support zero-touch bootstrap across
a not configured network though.
A.3. ACP Neighbor discovery protocol selection
This section discusses why GRASP DULL was chosen as the discovery
protocol for L2 adjacent candidate ACP neighbors. The contenders
considered where GRASP, mDNS or LLDP.
A.3.1. LLDP
LLDP and Cisco's earlier Cisco Discovery Protocol (CDP) are example
of L2 discovery protocols that terminate their messages on L2 ports.
If those protocols would be chosen for ACP neighbor discovery, ACP
neighbor discovery would therefore also terminate on L2 ports. This
would prevent ACP construction over non-ACP capable but LLDP or CDP
enabled L2 switches. LLDP has extensions using different MAC
addresses and this could have been an option for ACP discovery as
well, but the additional required IEEE standardization and definition
of a profile for such a modified instance of LLDP seemed to be more
work than the benefit of "reusing the existing protocol" LLDP for
this very simple purpose.
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A.3.2. mDNS and L2 support
Multicast DNNS (mDNS) [RFC6762] with DNS Service Discovery (DNS-SD)
Resource Records (RRs) as defined in [RFC6763] is a key contender as
an ACP discovery protocol. because it relies on link-local IP
multicast, it does operates at the subnet level, and is also found in
L2 switches. The authors of this document are not aware of mDNS
implementation that terminate their mDNS messages on L2 ports instead
of the subnet level. If mDNS was used as the ACP discovery mechanism
on an ACP capable (L3)/L2 switch as outlined in Section 7, then this
would be necessary to implement. It is likely that termination of
mDNS messages could only be applied to all mDNS messages from such a
port, which would then make it necessary to software forward any non-
ACP related mDNS messages to maintain prior non-ACP mDNS
functionality. Adding support for ACP into such L2 switches with
mDNS could therefore create regression problems for prior mDNS
functionality on those nodes. With low performance of software
forwarding in many L2 switches, this could also make the ACP risky to
support on such L2 switches.
A.3.3. Why DULL GRASP
LLDP was not considered because of the above mentioned issues. mDNS
was not selected because of the above L2 mDNS considerations and
because of the following additional points:
If mDNS was not already existing in a node, it would be more work to
implement than DULL GRASP, and if an existing implementation of mDNS
was used, it would likely be more code space than a separate
implementation of DULL GRASP or a shared implementation of DULL GRASP
and GRASP in the ACP.
A.4. Choice of routing protocol (RPL)
This section motivates why RPL - "IPv6 Routing Protocol for Low-Power
and Lossy Networks ([RFC6550] was chosen as the default (and in this
specification only) routing protocol for the ACP. The choice and
above explained profile was derived from a pre-standard
implementation of ACP that was successfully deployed in operational
networks.
Requirements for routing in the ACP are:
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* Self-management: The ACP must build automatically, without human
intervention. Therefore, routing protocol must also work
completely automatically. RPL is a simple, self-managing
protocol, which does not require zones or areas; it is also self-
configuring, since configuration is carried as part of the
protocol (see Section 6.7.6 of [RFC6550]).
* Scale: The ACP builds over an entire domain, which could be a
large enterprise or service provider network. The routing
protocol must therefore support domains of 100,000 nodes or more,
ideally without the need for zoning or separation into areas. RPL
has this scale property. This is based on extensive use of
default routing.
* Low resource consumption: The ACP supports traditional network
infrastructure, thus runs in addition to traditional protocols.
The ACP, and specifically the routing protocol must have low
resource consumption both in terms of memory and CPU requirements.
Specifically, at edge nodes, where memory and CPU are scarce,
consumption should be minimal. RPL builds a DODAG, where the main
resource consumption is at the root of the DODAG. The closer to
the edge of the network, the less state needs to be maintained.
This adapts nicely to the typical network design. Also, all
changes below a common parent node are kept below that parent
node.
* Support for unstructured address space: In the Autonomic
Networking Infrastructure, node addresses are identifiers, and may
not be assigned in a topological way. Also, nodes may move
topologically, without changing their address. Therefore, the
routing protocol must support completely unstructured address
space. RPL is specifically made for mobile ad-hoc networks, with
no assumptions on topologically aligned addressing.
* Modularity: To keep the initial implementation small, yet allow
later for more complex methods, it is highly desirable that the
routing protocol has a simple base functionality, but can import
new functional modules if needed. RPL has this property with the
concept of "objective function", which is a plugin to modify
routing behavior.
* Extensibility: Since the Autonomic Networking Infrastructure is a
new concept, it is likely that changes in the way of operation
will happen over time. RPL allows for new objective functions to
be introduced later, which allow changes to the way the routing
protocol creates the DAGs.
* Multi-topology support: It may become necessary in the future to
support more than one DODAG for different purposes, using
different objective functions. RPL allow for the creation of
several parallel DODAGs, should this be required. This could be
used to create different topologies to reach different roots.
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* No need for path optimization: RPL does not necessarily compute
the optimal path between any two nodes. However, the ACP does not
require this today, since it carries mainly non-delay-sensitive
feedback loops. It is possible that different optimization
schemes become necessary in the future, but RPL can be expanded
(see point "Extensibility" above).
A.5. ACP Information Distribution and multicast
IP multicast is not used by the ACP because the ANI (Autonomic
Networking Infrastructure) itself does not require IP multicast but
only service announcement/discovery. Using IP multicast for that
would have made it necessary to develop a zero-touch auto configuring
solution for ASM (Any Source Multicast - the original form of IP
multicast defined in [RFC1112]), which would be quite complex and
difficult to justify. One aspect of complexity where no attempt at a
solution has been described in IETF documents is the automatic-
selection of routers that should be PIM Sparse Mode (PIM-SM)
Rendezvous Points (RPs) (see [RFC7761]). The other aspects of
complexity are the implementation of MLD ([RFC4604]), PIM-SM and
Anycast-RP (see [RFC4610]). If those implementations already exist
in a product, then they would be very likely tied to accelerated
forwarding which consumes hardware resources, and that in return is
difficult to justify as a cost of performing only service discovery.
Some future ASA may need high performance in-network data
replication. That is the case when the use of IP multicast is
justified. Such an ASA can then use service discovery from ACP
GRASP, and then they do not need ASM but only SSM (Source Specific
Multicast, see [RFC4607]) for the IP multicast replication. SSM
itself can simply be enabled in the Data-Plane (or even in an update
to the ACP) without any other configuration than just enabling it on
all nodes and only requires a simpler version of MLD (see [RFC5790]).
LSP (Link State Protocol) based IGP routing protocols typically have
a mechanism to flood information, and such a mechanism could be used
to flood GRASP objectives by defining them to be information of that
IGP. This would be a possible optimization in future variations of
the ACP that do use an LSP routing protocol. Note though that such a
mechanism would not work easily for GRASP M_DISCOVERY messages which
are intelligently (constrained) flooded not across the whole ACP, but
only up to a node where a responder is found. We do expect that many
future services in ASA will have only few consuming ASA, and for
those cases, M_DISCOVERY is the more efficient method than flooding
across the whole domain.
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Because the ACP uses RPL, one desirable future extension is to use
RPLs existing notion of DODAG, which are loop-free distribution
trees, to make GRASP flooding more efficient both for M_FLOOD and
M_DISCOVERY. See Section 6.13.5 how this will be specifically
beneficial when using NBMA interfaces. This is not currently
specified in this document because it is not quite clear yet what
exactly the implications are to make GRASP flooding depend on RPL
DODAG convergence and how difficult it would be to let GRASP flooding
access the DODAG information.
A.6. CAs, domains and routing subdomains
There is a wide range of setting up different ACP solution by
appropriately using CAs and the domain and rsub elements in the acp-
node-name in the domain certificate. We summarize these options here
as they have been explained in different parts of the document in
before and discuss possible and desirable extensions:
An ACP domain is the set of all ACP nodes that can authenticate each
other as belonging to the same ACP network using the ACP domain
membership check (Section 6.2.3). GRASP inside the ACP is run across
all transitively connected ACP nodes in a domain.
The rsub element in the acp-node-name permits the use of addresses
from different ULA prefixes. One use case is to create multiple
physical networks that initially may be separated with one ACP domain
but different routing subdomains, so that all nodes can mutual trust
their ACP certificates (not depending on rsub) and so that they could
connect later together into a contiguous ACP network.
One instance of such a use case is an ACP for regions interconnected
via a non-ACP enabled core, for example due to the absence of product
support for ACP on the core nodes. ACP connect configurations as
defined in this document can be used to extend and interconnect those
ACP islands to the NOC and merge them into a single ACP when later
that product support gap is closed.
Note that RPL scales very well. It is not necessary to use multiple
routing subdomains to scale ACP domains in a way that would be
required if other routing protocols where used. They exist only as
options for the above mentioned reasons.
If different ACP domains are to be created that should not allow to
connect to each other by default, these ACP domains simply need to
have different domain elements in the acp-node-name. These domain
elements can be arbitrary, including subdomains of one another:
Domains "example.com" and "research.example.com" are separate domains
if both are domain elements in the acp-node-name of certificates.
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It is not necessary to have a separate CA for different ACP domains:
an operator can use a single CA to sign certificates for multiple ACP
domains that are not allowed to connect to each other because the
checks for ACP adjacencies includes comparison of the domain part.
If multiple independent networks choose the same domain name but had
their own CA, these would not form a single ACP domain because of CA
mismatch. Therefore, there is no problem in choosing domain names
that are potentially also used by others. Nevertheless it is highly
recommended to use domain names that one can have high probability to
be unique. It is recommended to use domain names that start with a
DNS domain names owned by the assigning organization and unique
within it. For example, "acp.example.com" if you own "example.com".
A.7. Intent for the ACP
Intent is the architecture component of autonomic networks according
to [I-D.ietf-anima-reference-model] that allows operators to issue
policies to the network. Its applicability for use is quite flexible
and freeform, with potential applications including policies flooded
across ACP GRASP and interpreted on every ACP node.
One concern for future definitions of Intent solutions is the problem
of circular dependencies when expressing Intent policies about the
ACP itself.
For example, Intent could indicate the desire to build an ACP across
all domains that have a common parent domain (without relying on the
rsub/routing-subdomain solution defined in this document). For
example, ACP nodes with domain "example.com", "access.example.com",
"core.example.com" and "city.core.example.com" should all establish
one single ACP.
If each domain has its own source of Intent, then the Intent would
simply have to allow adding the peer domains TA and domain names to
the parameters for the ACP domain membership check (Section 6.2.3) so
that nodes from those other domains are accepted as ACP peers.
If this Intent was to be originated only from one domain, it could
likely not be made to work because the other domains will not build
any ACP connection amongst each other, whether they use the same or
different CA due to the ACP domain membership check.
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If the domains use the same CA one could change the ACP setup to
permit for the ACP to be established between two ACP nodes with
different acp-domain-names, but only for the purpose of disseminating
limited information, such as Intent, but not to set up full ACP
connectivity, specifically not RPL routing and passing of arbitrary
GRASP information. Unless the Intent policies permit this to happen
across domain boundaries.
This type of approach where the ACP first allows Intent to operate
and only then sets up the rest of ACP connectivity based on Intent
policy could also be used to enable Intent policies that would limit
functionality across the ACP inside a domain, as long as no policy
would disturb the distribution of Intent. For example, to limit
reachability across the ACP to certain type of nodes or locations of
nodes.
A.8. Adopting ACP concepts for other environments
The ACP as specified in this document is very explicit about the
choice of options to allow interoperable implementations. The
choices made may not be the best for all environments, but the
concepts used by the ACP can be used to build derived solutions:
The ACP specifies the use of ULA and deriving its prefix from the
domain name so that no address allocation is required to deploy the
ACP. The ACP will equally work not using ULA but any other /48 IPv6
prefix. This prefix could simply be a configuration of the ACP
registrars (for example when using BRSKI) to enroll the domain
certificates - instead of the ACP registrar deriving the /48 ULA
prefix from the AN domain name.
Some solutions may already have an auto-addressing scheme, for
example derived from existing unique device identifiers (e.g., MAC
addresses). In those cases it may not be desirable to assign
addresses to devices via the ACP address information field in the way
described in this document. The certificate may simply serve to
identify the ACP domain, and the address field could be omitted. The
only fix required in the remaining way the ACP operate is to define
another element in the domain certificate for the two peers to decide
who is the Decider and who is the Follower during secure channel
building. Note though that future work may leverage the acp address
to authenticate "ownership" of the address by the device. If the
address used by a device is derived from some pre-existing permanent
local ID (such as MAC address), then it would be useful to store that
address in the certificate using the format of the access address
information field or in a similar way.
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The ACP is defined as a separate VRF because it intends to support
well managed networks with a wide variety of configurations.
Therefore, reliable, configuration-indestructible connectivity cannot
be achieved from the Data-Plane itself. In solutions where all
transit connectivity impacting functions are fully automated
(including security), indestructible and resilient, it would be
possible to eliminate the need for the ACP to be a separate VRF.
Consider the most simple example system in which there is no separate
Data-Plane, but the ACP is the Data-Plane. Add BRSKI, and it becomes
a fully autonomic network - except that it does not support automatic
addressing for user equipment. This gap can then be closed for
example by adding a solution derived from
[I-D.ietf-anima-prefix-management].
TCP/TLS as the protocols to provide reliability and security to GRASP
in the ACP may not be the preferred choice in constrained networks.
For example, CoAP/DTLS (Constrained Application Protocol) may be
preferred where they are already used, allowing to reduce the
additional code space footprint for the ACP on those devices. Hop-
by-hop reliability for ACP GRASP messages could be made to support
protocols like DTLS by adding the same type of negotiation as defined
in this document for ACP secure channel protocol negotiation. End-
to-end GRASP connections can be made to select their transport
protocol in future extensions of the ACP meant to better support
constrained devices by indicating the supported transport protocols
(e.g. TLS/DTLS) via GRASP parameters of the GRASP objective through
which the transport endpoint is discovered.
The routing protocol RPL used for the ACP does explicitly not
optimize for shortest paths and fastest convergence. Variations of
the ACP may want to use a different routing protocol or introduce
more advanced RPL profiles.
Variations such as what routing protocol to use, or whether to
instantiate an ACP in a VRF or (as suggested above) as the actual
Data-Plane, can be automatically chosen in implementations built to
support multiple options by deriving them from future parameters in
the certificate. Parameters in certificates should be limited to
those that would not need to be changed more often than certificates
would need to be updated anyhow; Or by ensuring that these parameters
can be provisioned before the variation of an ACP is activated in a
node. Using BRSKI, this could be done for example as additional
follow-up signaling directly after the certificate enrollment, still
leveraging the BRSKI TLS connection and therefore not introducing any
additional connectivity requirements.
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Last but not least, secure channel protocols including their
encapsulations are easily added to ACP solutions. ACP hop-by-hop
network layer secure channels could also be replaced by end-to-end
security plus other means for infrastructure protection. Any future
network OAM should always use end-to-end security anyhow and can
leverage the domain certificates and is therefore not dependent on
security to be provided for by ACP secure channels.
A.9. Further (future) options
A.9.1. Auto-aggregation of routes
Routing in the ACP according to this specification only leverages the
standard RPL mechanism of route optimization, e.g. keeping only
routes that are not towards the RPL root. This is known to scale to
networks with 20,000 or more nodes. There is no auto-aggregation of
routes for /48 ULA prefixes (when using rsub in the acp-node-name)
and/or Zone-ID based prefixes.
Automatic assignment of Zone-ID and auto-aggregation of routes could
be achieved for example by configuring zone-boundaries, announcing
via GRASP into the zones the zone parameters (zone-ID and /48 ULA
prefix) and auto-aggregating routes on the zone-boundaries. Nodes
would assign their Zone-ID and potentially even /48 prefix based on
the GRASP announcements.
A.9.2. More options for avoiding IPv6 Data-Plane dependencies
As described in Section 6.13.2, the ACP depends on the Data-Plane to
establish IPv6 link-local addressing on interfaces. Using a separate
MAC address for the ACP allows to fully isolate the ACP from the
Data-Plane in a way that is compatible with this specification. It
is also an ideal option when using Single-root input/output
virtualization (SR-IOV - see https://en.wikipedia.org/wiki/Single-
root_input/output_virtualization) in an implementation to isolate the
ACP because different SR-IOV interfaces use different MAC addresses.
When additional MAC address(es) are not available, separation of the
ACP could be done at different demux points. The same subnet
interface could have a separate IPv6 interface for the ACP and Data-
Plane and therefore separate link-local addresses for both, where the
ACP interface is non-configurable on the Data-Plane. This too would
be compatible with this specification and not impact
interoperability.
An option that would require additional specification is to use a
different Ethertype from 0x86DD (IPv6) to encapsulate IPv6 packets
for the ACP. This would be a similar approach as used for IP
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authentication packets in [IEEE-802.1X] which use the Extensible
Authentication Protocol over Local Area Network (EAPoL) ethertype
(0x88A2).
Note that in the case of ANI nodes, all the above considerations
equally apply to the encapsulation of BRSKI packets including GRASP
used for BRSKI.
A.9.3. ACP APIs and operational models (YANG)
Future work should define YANG ([RFC7950]) data model and/or node
internal APIs to monitor and manage the ACP.
Support for the ACP Adjacency Table (Section 6.3) and ACP GRASP need
to be included into such model/API.
A.9.4. RPL enhancements
..... USA ...... ..... Europe ......
NOC1 NOC2
| |
| metric 100 |
ACP1 --------------------------- ACP2 .
| | . WAN
| metric 10 metric 20 | . Core
| | .
ACP3 --------------------------- ACP4 .
| metric 100 |
| | .
| | . Sites
ACP10 ACP11 .
Figure 19: Dual NOC
The profile for RPL specified in this document builds only one
spanning-tree path set to a root, typically a registrar in one NOC.
In the presence of multiple NOCs, routing toward the non-root NOCs
may be suboptimal. Figure 19 shows an extreme example. Assuming
that node ACP1 becomes the RPL root, traffic between ACP11 and NOC2
will pass through ACP4-ACP3-ACP1-ACP2 instead of ACP4-ACP2 because
the RPL calculated DODAG/routes are shortest paths towards the RPL
root.
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To overcome these limitations, extensions/modifications to the RPL
profile can provide optimality for multiple NOCs. This requires
utilizing Data-Plane artifact including IPinIP encap/decap on ACP
routers and processing of IPv6 RPI headers. Alternatively, (Src,Dst)
routing table entries could be used.
Flooding of ACP GRASP messages can be further constrained and
therefore optimized by flooding only via links that are part of the
RPL DODAG.
A.9.5. Role assignments
ACP connect is an explicit mechanism to "leak" ACP traffic explicitly
(for example in a NOC). It is therefore also a possible security gap
when it is easy to enable ACP connect on arbitrary compromised ACP
nodes.
One simple solution is to define an extension in the ACP certificates
ACP information field indicating the permission for ACP connect to be
configured on that ACP node. This could similarly be done to decide
whether a node is permitted to be a registrar or not.
Tying the permitted "roles" of an ACP node to the ACP certificate
provides fairly strong protection against misconfiguration, but is
still subject to code modifications.
Another interesting role to assign to certificates is that of a NOC
node. This would allow to limit certain type of connections such as
OAM TLS connections to only NOC initiator or responders.
A.9.6. Autonomic L3 transit
In this specification, the ACP can only establish autonomic
connectivity across L2 hops and only explicitly configured options to
tunnel across L3. Future work should specify mechanisms to
automatically tunnel ACP across L3 networks. A hub&spoke option
would allow to tunnel across the Internet to a cloud or central
instance of the ACP, a peer-to-peer tunneling mechanism could tunnel
ACP islands across an L3VPN infrastructure.
A.9.7. Diagnostics
Section 9.1 describes diagnostics options that can be done without
changing the external, interoperability affecting characteristics of
ACP implementations.
Even better diagnostics of ACP operations is possible with additional
signaling extensions, such as:
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1. Consider if LLDP should be a recommended functionality for ANI
devices to improve diagnostics, and if so, which information
elements it should signal (noting that such information is
conveyed in an insecure manner). Includes potentially new
information elements.
2. In alternative to LLDP, A DULL GRASP diagnostics objective could
be defined to carry these information elements.
3. The IDevID certificate of BRSKI pledges should be included in the
selected insecure diagnostics option. This may be undesirable
when exposure of device information is seen as too much of a
security issue (ability to deduce possible attack vectors from
device model for example).
4. A richer set of diagnostics information should be made available
via the secured ACP channels, using either single-hop GRASP or
network wide "topology discovery" mechanisms.
A.9.8. Avoiding and dealing with compromised ACP nodes
Compromised ACP nodes pose the biggest risk to the operations of the
network. The most common type of compromise is leakage of
credentials to manage/configure the device and the application of
malicious configuration including the change of access credentials,
but not the change of software. Most of today's networking equipment
should have secure boot/software infrastructure anyhow, so attacks
that introduce malicious software should be a lot harder.
The most important aspect of security design against these type of
attacks is to eliminate password based configuration access methods
and instead rely on certificate based credentials handed out only to
nodes where it is clear that the private keys cannot leak. This
limits unexpected propagation of credentials.
If password based credentials to configure devices still need to be
supported, they must not be locally configurable, but only be
remotely provisioned or verified (through protocols like RADIUS or
Diameter), and there must be no local configuration permitting to
change these authentication mechanisms, but ideally they should be
autoconfiguring across the ACP. See
[I-D.eckert-anima-noc-autoconfig].
Without physical access to the compromised device, attackers with
access to configuration should not be able to break the ACP
connectivity, even when they can break or otherwise manipulate
(spoof) the Data-Plane connectivity through configuration. To
achieve this, it is necessary to avoid providing configuration
options for the ACP, such as enabling/disabling it on interfaces.
For example, there could be an ACP configuration that locks down the
current ACP config unless factory reset is done.
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With such means, the valid administration has the best chances to
maintain access to ACP nodes, discover malicious configuration though
ongoing configuration tracking from central locations for example,
and to react accordingly.
The primary reaction is withdrawal/change of credentials, terminate
malicious existing management sessions and fixing the configuration.
Ensuring that management sessions using invalidated credentials are
terminated automatically without recourse will likely require new
work.
Only when these steps are not feasible would it be necessary to
revoke or expire the ACP certificate credentials and consider the
node kicked off the network - until the situation can be further
rectified, likely requiring direct physical access to the node.
Without extensions, compromised ACP nodes can only be removed from
the ACP at the speed of CRL/OCSP information refresh or expiry (and
non-removal) of short lived certificates. Future extensions to the
ACP could for example use GRASP flooding distribution of triggered
updates of CRL/OCSP or explicit removal indication of the compromised
nodes domain certificate.
A.9.9. Detecting ACP secure channel downgrade attacks
The following text proposes a mechanism to protect against downgrade
attacks without introducing a new specialized UPFRONT GRASP secure
channel mechanism. Instead, it relies on running GRASP after
establishing a secure channel protocol to verify if the established
secure channel option could have been the result of a MITM downgrade
attack:
MITM attackers can force downgrade attacks for ACP secure channel
selection by filtering/modifying DULL GRASP messages and/or actual
secure channel data packets. For example, if at some point in time
DTLS traffic could be easier decrypted than traffic of IKEv2, the
MITM could filter all IKEv2 packets to force ACP nodes to use DTLS
(assuming the ACP nodes in question supported both DTLS and IKEv2).
For cases where such MITM attacks are not capable to inject malicious
traffic (but only to decrypt the traffic), a downgrade attack could
be discovered after a secure channel connection is established, for
example by use of the following type of mechanism:
After the secure channel connection is established, the two ACP peers
negotiate via an appropriate (To Be Defined) GRASP negotiation which
ACP secure channel protocol should have been selected between them
(in the absence of a MITM attacker). This negotiation would have to
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signal the DULL GRASP announced ACP secure channel options by each
peer followed by an announcement of the preferred secure channel
protocol by the ACP peer that is the Decider in the secure channel
setup, e.g. the ACP peer that is deciding which secure channel
protocol to pick. If that chosen secure channel protocol is
different from the one that actually was chosen, then this mismatch
is an indication that there is a MITM attacker or other similar issue
(firewall prohibiting the use of specific protocols) that caused a
non-preferred secure channel protocol to be chosen. This discovery
could then result in mitigation options such as logging and ensuing
investigations.
Appendix B. Unfinished considerations (To Be Removed From RFC)
[RFC-Editor: This whole appendix B. and its subsections to be removed
for the RFC.
This appendix contains unfinished considerations that are removed
from the RFC, they are maintained in this draft as a log of the state
of discussion and point of reference. Together with this appendix,
also the references pointing to it are marked to be removed from the
RFC because no consensus could be reached that a self-reference to a
draft version of the RFC is an appropriate breadcrumb to point to
unfinished considerations.
The authors plan to move these considerations into a new target
informational draft, please look for draft-eckert-anima-acp-
considerations.
B.1. Considerations for improving secure channel negotiation
Proposed text from Benjamin Kaduk. It is suggested to replace the
text of appendix A.6 in previous versions of this draft (up to
version 29).
The discovery procedure in this specification for low-level ACP
channel support by layer-2 peers involves DULL GRASP and attempting
(usually in parallel) to establish all supported channel types,
learning the peer ACP address and correspondingly the assignment of
Decider and Follower roles, and tearing down all channels other than
the one preferred by the Decider. This procedure, in general,
becomes resource intensive as the number of possible secure channels
grows; even worse, under some threat models, the security of the
discovery result is only as strong as the weakest supported secure
channel protocol. Furthermore, the unilateral determination of
"best" channel type by the Decider does not result in the optimal
outcome in all possible scenarios.
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This situation is tolerable at present, with only two secure channels
(DTLS and IPsec) defined, but long-term agility in the vein of
[BCP201] will require the introduction of an alternate discovery/
negotiation procedure. While IKEv2 is the IETF standard protocol for
negotiating security associations, it currently does not have a
defined mechanism flexible enough to negotiate the parameters needed
for, e.g., an ACP DTLS channel, let alone for allowing ACP peers to
indicate their preference metrics for channel selection. Such a
mechanism or mechanisms could be defined, but if ACP agility requires
introducing a new channel type, for example MacSec, IKEv2 would again
need to be extended in order to negotiate an ACP MacSec association.
Making ACP channel agility dependent on updates to IKEv2 is likely to
result in obstacles due to different timescales of evolution, since
IKEv2 implementations help form the core of Internet-scale security
infrastructure and must accordingly be robust and thoroughly tested.
Accordingly, a dedicated ACP channel negotiation mechanism is
appropriate as a way to provide long-term algorithm and secure-
channel protocol agility. Such a mechanism is not currently defined,
but one possible design is as follows. A new DULL GRASP objective is
defined to indicate the GRASP-over-TLS channel, which is by
definition preferred to other channel types (including DTLS and
IPsec). When both peers advertise support for GRASP-over-TLS, GRASP-
over-TLS must run to completion before other channel types are
attempted. The GRASP-over-TLS channel performs the necessary
negotiation by establishing a TLS connection between the peers and
using that connection to secure a dedicated GRASP instance for
negotiating supported channel types and preference metrics. This
provides a rich language for determining what secure channel protocol
to use for the ACP link while taking into account the capabilities
and preferences of the ACP peers, all protected by the security of
the TLS channel.
B.2. ACP address verification
The AcpNodeName of most ACP nodes contains in the acp-address field
the primary ACP address to be used by the node for end-to-end
connections across ACP secure channels. Nevertheless, there is no
verification of an ACP peers address specified in this document.
This section explains the current understanding as to why this is not
done.
Not all ACP nodes will have an actual IPv6 address in the acp-address
field of their AcpNodeName. Those who do not include nodes that do
not support ACP secure channels, such as pre-existing NOC equipment
that only connects to the ACP via ACP connect interfaces. Likewise,
future ACP node type that may want to have their Node-ID not be
defined by an ACP registrar, but differently cannot have the ACP
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address be provided in their ACP certificate where it would be
defined by the registrar. In result, any scheme that would rely on
verification of the acp-address in the ACP certificate would only
apply to a subset of ACP nodes.
The transport stack network layer address used for ACP secure
channels is not the acp-address. For automatically established ACP
secure channels, it is a link-local IPv6 address. For explicitly
configured ACP secure channels (to reach across non ACP L3 network
segments), the address is any IPv4 or IPv6 address routable to that
remote destination.
When the acp-address is actually used across the ACP, it can only be
verified by a peer when the peer has the certificate of the peer.
Unless further higher layer mechanisms are developed on top of the
ACP (for example via ASA), the only mechanism to access a peers ACP
certificate is for secure connections in which the peers certificates
are exchanged and cryptographically verified, e.g. TLS and DTLS.
Initially, it is expected that the ACP will carry many legacy network
management control connections that unfortunately not end-to-end
authenticated but that are solely protected by being carried across
the ACP secure channels. ACP address verification therefore cannot
be used for such connections without additional higher layer
components.
For the remaining (TLS/DTLS) connections for which address
verification can be used, the main question is: what additional
benefit would address verification provide?
The main value that transport stack network layer address
verification could provide for these type of connections would be the
discovery of on-path transport proxies. For example, in case of
BRSKI, pledges connect to an ACP registrar via an ASA implementing a
TCP proxy because the pledge itself has at that point in time no ACP
certificate valid to build ACP secure channels and hence needs to
rely on such a proxy. This is one example where such a TCP proxy is
required and not a form of attack.
In general, on path TCP proxies could be a form of attack, but it
stands to reason, that an attacker that manages to enable a malicious
TCP proxy could likely equally build a transparent proxy not changing
the network layer addresses. Only when the attacker operates off-
path would this option not be possible. Such attacks could indeed be
possible: An impaired ACP node could announce itself as another
service instance for a service whose utilization it wants to attack.
It could then attempt to look like a valid server by simply TCP
proxying the clients connections to a valid server and then attack
the connections passing through it (passive decrypting or passive
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fingerprint analysis). But like the BRSKI proxy, this behavior could
be perfectly legitimate and not an attack. For example, TCP has in
the past often suffered from performance issues across difficult
(high capacity, high loss) paths, and TCP proxies where and are being
used simply as a tool for isolating such path segments (such as a
WAN), and providing caching and local-retransmit of in-transit
packets, reducing the effective path segment capacity.
As explained elsewhere in this document already, considerations for
these type of attack are therefore outside the scope of the ACP but
fundametal to further design of the ASA infrastructure. Beyond
distinguishing whether a TCP proxy would be beneficial or malicious,
the even more fundamental question is how to determine from a
multitude of service announcements which instance is the most
trustworthy and functionally best. In the Internet/web, this
question is NOT solved inside the network but through off-net human
interaction ("trust me, the best search engine is www.<insert-your-
personal-recommendation>.com").
B.3. Public CA considerations
Public CAs are outside the scope of this document for the following
reasons. This appendix describes the current state of understanding
for those interested to consider utilizing public CA for the ACP in
the future.
If public CA where to be used to enroll ACP nodes and act as TA, this
would require a model in which the public CA would be able to assert
the ownership of the information requested in the certificate,
especially the AcpNodeName, for example mitigated by the domain
registrar(s). Due to the use of a new, ACP unique encoding of the
AcpNodeName, there is no mechanism for public CA to do so. More
importantly though, isolation between ACPs of disjoint operated ACPs
is achieved in the current ACP design through disjoint TA. A public
CA is in general based on a single (set of) TA shared across all
certificates signed by the CA.
Due to the fact that the ACP domain membership check also validates
that a peers domain name in the AcpNodeName matches that of the ACP
node itself, it would be possible to use the same TA across disjoint
ACP domains, but the security and attack implications of such an
approach are beyond the scope of this document.
The use of ULA addresses in the AcpNodeName is another novel aspect
for certificates from a possible public CA. Typically, ULA addresses
are not meant to be signed by a public CA when carried in an address
field, because there is no ownership of a particular ULA address in
the scope of the Internet, which is what public CA operate on.
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Nevertheless, the ULA addresses used by the ACP are scoped to be
valid only within the confines of a specific ACP as defined by the
domain name in the AcpNodeName. However, this understanding has not
been reviewed or accepted by any bodies responsible for policies of
public CA.
Because in this specification, ACPs are isolated from each other
primarily by their TA, when a public CA would intend to sign ACP
certificates and using a single TA to sign TA of ACP certificates
from different operators/domain, it could do so by ensuring that the
domain name in the AcpNodeName was a globally owned DNS ACP domain
name of the organization, and beyond that, it would need to validate
that the ACP registrar of that domain who is mitigating the
enrollment is authorized to vouch for the ownership of the acp-
address within the scope of the ACP domain name.
B.4. Hardening DULL GRASP considerations
DULL GRASP suffers from similar type of DoS attacks as many link-
local multicast discovery protocols, for example mDNS. Attackers on
a subnet may be able to inject malicious DULL GRASP messages that are
indistinguishable from non-malicious DULL GRASP messages to create
Denial-of-Service (DoS) attacks that force ACP nodes to attempt many
unsuccessful ACP secure channel connections.
When an ACP node sees multiple AN_ACP objectives for the same secure
channel protocol on different transport addresses, it could prefer
connecting via the well-known transport address if the secure channel
method has one, such as UDP port 500 for IKEv2. For protocols such
as (ACP secure channel over) DTLS for which there are no well defined
port number, this heuristic does not provide benefits though.
DoS attack with port numbers can also be eliminated by relying on
well known-port numbers implied by the GRASP method-name. For
example, a future service name of "DTLSacp" could be defined to be
associated only to a newly to be assigned well known UDP port for ACP
over DTLS, and the port number in the GRASP transport address
information would be ignored. Note that there is already a variety
of ports assigned to specific protocols over DTLS by IANA, so
especially for DTLS this would not be uncommon.
Authors' Addresses
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Toerless Eckert (editor)
Futurewei Technologies Inc. USA
2330 Central Expy
Santa Clara, 95050
United States of America
Email: tte+ietf@cs.fau.de
Michael H. Behringer (editor)
Email: michael.h.behringer@gmail.com
Steinthor Bjarnason
Arbor Networks
2727 South State Street, Suite 200
Ann Arbor, MI 48104
United States
Email: sbjarnason@arbor.net
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