Internet DRAFT - draft-ietf-anima-stable-connectivity
draft-ietf-anima-stable-connectivity
ANIMA T. Eckert, Ed.
Internet-Draft Huawei
Intended status: Informational M. Behringer
Expires: August 9, 2018 February 5, 2018
Using Autonomic Control Plane for Stable Connectivity of Network OAM
draft-ietf-anima-stable-connectivity-10
Abstract
OAM (Operations, Administration and Maintenance - as per BCP161,
(RFC6291) processes for data networks are often subject to the
problem of circular dependencies when relying on connectivity
provided by the network to be managed for the OAM purposes.
Provisioning while bringing up devices and networks tends to be more
difficult to automate than service provisioning later on, changes in
core network functions impacting reachability cannot be automated
because of ongoing connectivity requirements for the OAM equipment
itself, and widely used OAM protocols are not secure enough to be
carried across the network without security concerns.
This document describes how to integrate OAM processes with an
autonomic control plane in order to provide stable and secure
connectivity for those OAM processes. This connectivity is not
subject to aforementioned circular dependencies.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 9, 2018.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Self-dependent OAM Connectivity . . . . . . . . . . . . . 3
1.2. Data Communication Networks (DCNs) . . . . . . . . . . . 3
1.3. Leveraging a generalized autonomic control plane . . . . 4
2. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Stable Connectivity for Centralized OAM . . . . . . . . . 5
2.1.1. Simple Connectivity for Non-GACP capable NMS Hosts . 6
2.1.2. Challenges and Limitation of Simple Connectivity . . 7
2.1.3. Simultaneous GACP and data-plane Connectivity . . . . 8
2.1.4. IPv4-only NMS Hosts . . . . . . . . . . . . . . . . . 9
2.1.5. Path Selection Policies . . . . . . . . . . . . . . . 12
2.1.6. Autonomic NOC Device/Applications . . . . . . . . . . 15
2.1.7. Encryption of data-plane connections . . . . . . . . 15
2.1.8. Long Term Direction of the Solution . . . . . . . . . 16
2.2. Stable Connectivity for Distributed Network/OAM . . . . . 17
3. Architectural Considerations . . . . . . . . . . . . . . . . 17
3.1. No IPv4 for GACP . . . . . . . . . . . . . . . . . . . . 17
4. Security Considerations . . . . . . . . . . . . . . . . . . . 18
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.1. Normative References . . . . . . . . . . . . . . . . . . 23
8.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
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1.1. Self-dependent OAM Connectivity
OAM (Operations, Administration and Maintenance - as per BCP161,
[RFC6291]) for data networks is often subject to the problem of
circular dependencies when relying on the connectivity service
provided by the network to be managed. OAM can easily but
unintentionally break the connectivity required for its own
operations. Avoiding these problems can lead to complexity in OAM.
This document describes this problem and how to use an autonomic
control plane to solve it without further OAM complexity:
The ability to perform OAM on a network device requires first the
execution of OAM necessary to create network connectivity to that
device in all intervening devices. This typically leads to
sequential, 'expanding ring configuration' from a NOC (Network
Operations Center). It also leads to tight dependencies between
provisioning tools and security enrollment of devices. Any process
that wants to enroll multiple devices along a newly deployed network
topology needs to tightly interlock with the provisioning process
that creates connectivity before the enrollment can move on to the
next device.
When performing change operations on a network, it likewise is
necessary to understand at any step of that process that there is no
interruption of connectivity that could lead to removal of
connectivity to remote devices. This includes especially change
provisioning of routing, forwarding, security and addressing policies
in the network that often occur through mergers and acquisitions, the
introduction of IPv6 or other mayor re-hauls in the infrastructure
design. Examples include change of an IGP or areas, PA (Provider
Aggregatable) to PI (Provider Independent) addressing, or systematic
topology changes (such as L2 to L3 changes).
All these circular dependencies make OAM complex and potentially
fragile. When automation is being used, for example through
provisioning systems, this complexity extends into that automation
software.
1.2. Data Communication Networks (DCNs)
In the late 1990s and early 2000, IP networks became the method of
choice to build separate OAM networks for the communications
infrastructure within Network Providers. This concept was
standardized in ITU-T G.7712/Y.1703 [ITUT] and called "Data
Communications Networks" (DCN). These were (and still are)
physically separate IP(/MPLS) networks that provide access to OAM
interfaces of all equipment that had to be managed, from PSTN (Public
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Switched Telephone Network) switches over optical equipment to
nowadays Ethernet and IP/MPLS production network equipment.
Such DCN provide stable connectivity not subject to aforementioned
problems because they are a separate network entirely, so change
configuration of the production IP network is done via the DCN but
never affects the DCN configuration. Of course, this approach comes
at a cost of buying and operating a separate network and this cost is
not feasible for many providers, most notably smaller providers, most
enterprises and typical IoT networks (Internet of Things).
1.3. Leveraging a generalized autonomic control plane
One of the goals of the IETF ANIMA (Autonomic Networking Integrated
Model and Approach ) working group is the specification of a secure
and automatically built inband management plane that provides similar
stable connectivity as a DCN, but without having to build a separate
DCN. It is clear that such 'in-band' approach can never achieve
fully the same level of separation, but the goal is to get as close
to it as possible.
This goal of this document is to discuss how such an inband
management plane can be used to support the DCN-like OAM use-case,
leverage its stable connectivity and details the options of deploying
it incrementally - short and long term.
The evolving ANIMA working groups specification
[I-D.ietf-anima-autonomic-control-plane] ) calls this inband
management plane the "Autonomic Control Plane" (ACP). The
discussions in this document are not depending on the specification
of that ACP, but only on a set of high level constraints decided
early on in the work for the ACP. Unless being specific about
details of the ACP, this document uses the term "Generalized ACP"
(GACP) and is applicable to any designs that meet those high level
constraints. For example - but not limited to - variations of the
ACP protocol choices.
The high level constraints of a GACP assumed and discussed in this
document are as follows:
VRF Isolation: The GACP is a virtual network ("VRF") across network
devices - its routing and forwarding are separate from other
routing and forwarding in the network devices. Non-GACP routing/
forwarding is called the "data-plane".
IPv6 only addressing: The GACP provides only IPv6 reachability. It
uses ULA addresses ([RFC4193]) that are routed in a location
independent fashion for example through per network device subnet
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prefixes. Automatic addressing in the GACP is therefore simple &
stable: it does not require allocation by address registries,
addresses are identifiers, they do not change when devices move,
and no engineering of the address space to the network topology is
necessary.
NOC connectivity: NOC equipment (controlling OAM operations) either
has access to the GACP directly or has an IP subnet connection to
a GACP-edge device.
Closed Group Security: GACP devices have cryptographic credentials
to mutually authenticate each other as members of a GACP. Traffic
across the GACP is authenticated with these credentials and then
encrypted. The only traffic permitted in & out of the GACP that
is not authenticated by these credentials is through explicit
configuration the traffic from/to the aforementioned non-GACP NOC
equipment with subnet connections to a GACP-edge device (as a
transition method).
The GACP must be built autonomic and its function must not be
disruptable by operator or automated (NMS/SDN) configuration/
provisioning actions. These are allowed to only impact the "data-
plane". This aspect is not currently covered in this document.
Instead, it focusses on the impact of the above constraints: IPv6
only, dual connectivity and security.
2. Solutions
2.1. Stable Connectivity for Centralized OAM
The ANI is the "Autonomic Networking Infrastructure" consisting of
secure zero touch Bootstrap (BRSKI -
[I-D.ietf-anima-bootstrapping-keyinfra]), GeneRic Autonomic Signaling
Protocol (GRASP - [I-D.ietf-anima-grasp]), and Autonomic Control
Plane (ACP - [I-D.ietf-anima-autonomic-control-plane]). Refer to
[I-D.ietf-anima-reference-model] for an overview of the ANI and how
its components interact and [RFC7575] for concepts and terminology of
ANI and autonomic networks.
This section describes stable connectivity for centralized OAM via
the GACP, for example via the ACP with or without a complete ANI,
starting by what we expect to be the most easy to deploy short-term
option. It then describes limitation and challenges of that approach
and their solutions/workarounds to finish with the preferred target
option of autonomic NOC devices in Section 2.1.6.
This order was chosen because it helps to explain how simple initial
use of a GACP can be, how difficult workarounds can become (and
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therefore what to avoid), and finally because one very promising
long-term solution alternative is exactly like the most easy short-
term solution only virtualized and automated.
In the most common case, OAM will be performed by one or more
applications running on a variety of centralized NOC systems that
communicate with network devices. We describe differently advanced
approaches to leverage a GACP for stable connectivity. There is a
wide range of options, some of which are simple, some more complex.
Three stages can be considered:
o There are simple options described in sections Section 2.1.1
through Section 2.1.3 that we consider to be good starting points
to operationalize the use of a GACP for stable connectivity today.
These options require only network and OAN/NOC device
configuration.
o The are workarounds to connect a GACP to non-IPv6 capable NOC
devices through the use of IPv4/IPv6 NAT (Network Address
Translation) as described in section Section 2.1.4. These
workarounds are not recommended but if such non-IPv6 capable NOC
devices need to be used longer term, then this is the only option
to connect them to a GACP.
o Near to long term options can provide all the desired operational,
zero touch and security benefits of an autonomic network, but a
range of details for this still have to be worked out and
development work on NOC/OAM equipment is necessary. These options
are discussed in sections Section 2.1.5 through Section 2.1.8.
2.1.1. Simple Connectivity for Non-GACP capable NMS Hosts
In the most simple candidate deployment case, the GACP extends all
the way into the NOC via one or more "GACP-edge-devices". See also
section 6.1 of [I-D.ietf-anima-autonomic-control-plane]. These
devices "leak" the (otherwise encrypted) GACP natively to NMS hosts.
They act as the default routers to those NMS hosts and provide them
with IPv6 connectivity into the GACP. NMS hosts with this setup need
to support IPv6 (see e.g. [RFC6434]) but require no other
modifications to leverage the GACP.
Note that even though the GACP only uses IPv6, it can of course
support OAM for any type of network deployment as long as the network
devices support the GACP: The data-plane can be IPv4 only, dual-stack
or IPv6 only. It is always separate from the GACP, therefore there
is no dependency between the GACP and the IP version(s) used in the
data-plane.
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This setup is sufficient for troubleshooting such as SSH into network
devices, NMS that performs SNMP read operations for status checking,
software downloads into autonomic devices, provisioning of devices
via NETCONF and so on. In conjunction with otherwise unmodified OAM
via separate NMS hosts it can provide a good subset of the stable
connectivity goals. The limitations of this approach are discussed
in the next section.
Because the GACP provides 'only' for IPv6 connectivity, and because
addressing provided by the GACP does not include any topological
addressing structure that operations in a NOC often relies on to
recognize where devices are on the network, it is likely highly
desirable to set up DNS (Domain Name System - see [RFC1034]) so that
the GACP IPv6 addresses of autonomic devices are known via domain
names that include the desired structure. For example, if DNS in the
network was set up with names for network devices as
devicename.noc.example.com, and the well-known structure of the data-
plane IPv4 addresses space was used by operators to infer the region
where a device is located in, then the GACP address of that device
could be set up as devicename_<region>.acp.noc.example.com, and
devicename.acp.noc.example.com could be a CNAME to
devicename_<region>.acp.noc.example.com. Note that many networks
already use names for network equipment where topological information
is included, even without a GACP.
2.1.2. Challenges and Limitation of Simple Connectivity
This simple connectivity of non-autonomic NMS hosts suffers from a
range of challenges (that is, operators may not be able to do it this
way) or limitations (that is, operator cannot achieve desired goals
with this setup). The following list summarizes these challenges and
limitations. The following sections describe additional mechanisms
to overcome them.
Note that these challenges and limitations exist because GACP is
primarily designed to support distributed ASA (Autonomic Service
Agent, a piece of autonomic software) in the most lightweight
fashion, but not mandatorily require support for additional
mechanisms to best support centralized NOC operations. It is this
document that describes additional (short term) workarounds and (long
term) extensions.
1. (Limitation) NMS hosts cannot directly probe whether the desired
so called 'data-plane' network connectivity works because they do
not directly have access to it. This problem is similar to
probing connectivity for other services (such as VPN services)
that they do not have direct access to, so the NOC may already
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employ appropriate mechanisms to deal with this issue (probing
proxies). See Section 2.1.3 for candidate solutions.
2. (Challenge) NMS hosts need to support IPv6 which often is still
not possible in enterprise networks. See Section 2.1.4 for some
workarounds.
3. (Limitation) Performance of the GACP may be limited versus normal
'data-plane' connectivity. The setup of the GACP will often
support only non-hardware accelerated forwarding. Running a
large amount of traffic through the GACP, especially for tasks
where it is not necessary will reduce its performance/
effectiveness for those operations where it is necessary or
highly desirable. See Section 2.1.5 for candidate solutions.
4. (Limitation) Security of the GACP is reduced by exposing the GACP
natively (and unencrypted) into a subnet in the NOC where the NOC
devices are attached to it. See Section 2.1.7 for candidate
solutions.
These four problems can be tackled independently of each other by
solution improvements. Combining some of these solutions
improvements together can lead towards a candidate long term
solution.
2.1.3. Simultaneous GACP and data-plane Connectivity
Simultaneous connectivity to both GACP and data-plane can be achieved
in a variety of ways. If the data-plane is IPv4-only, then any
method for dual-stack attachment of the NOC device/application will
suffice: IPv6 connectivity from the NOC provides access via the GACP,
IPv4 will provide access via the data-plane. If as explained above
in the simple case, an autonomic device supports native attachment to
the GACP, and the existing NOC setup is IPv4 only, then it could be
sufficient to attach the GACP device(s) as the IPv6 default router to
the NOC subnet and keep the existing IPv4 default router setup
unchanged.
If the data-plane of the network is also supporting IPv6, then the
most compatible setup for NOC devices is to have two IPv6 interfaces.
One virtual ((e.g. via IEEE 802.1Q [IEEE802.1Q]) or physical
interface connecting to a data-plane subnet, and another into an GACP
connect subnet. See section 8.1 of
[I-D.ietf-anima-autonomic-control-plane] for more details. That
document also specifies how the NOC devices can receive auto
configured addressing and routes towards the ACP connect subnet if it
supports [RFC6724] and [RFC4191].
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Configuring a second interface on a NOC host may be impossible or be
seen as undesired complexity. In that case the GACP edge device
needs to provide support for a "Combined ACP and data-plane
interface" as also described in section 8.1 of
[I-D.ietf-anima-autonomic-control-plane]. This setup may not work
with auto configuration and all NOC host network stacks due to
limitations in those network stacks. They need to be able to perform
RFC6724 source address selection rule 5.5 including caching of next-
hop information.
For security reasons, it is not considered appropriate to connect a
non-GACP router to a GACP connect interface. The reason is that the
GACP is a secured network domain and all NOC devices connecting via
GACP connect interfaces are also part of that secure domain - the
main difference is that the physical link between the GACP edge
device and the NOC devices is not authenticated/encrypted and
therefore, needs to be physically secured. If the secure GACP was
extendable via untrusted routers then it would be a lot more
difficult to verify the secure domain assertion. Therefore the GACP
edge devices are not supposed to redistribute routes from non-GACP
routers into the GACP.
2.1.4. IPv4-only NMS Hosts
One architectural expectation for the GACP as described in
Section 1.3 is that all devices that want to use the GACP do support
IPv6. Including NMS hosts. Note that this expectation does not
imply any requirements against the data-plane, especially no need to
support IPv6 in it. The data-plane could be IPv4 only, IPv6 only,
dual stack or it may not need to have any IP host stack on the
network devices.
The implication of this architectural decision is the potential need
for short-term workarounds when the operational practices in a
network do not yet meet these target expectations. This section
explains when and why these workarounds may be operationally
necessary and describes them. However, the long term goal is to
upgrade all NMS hosts to native IPv6, so the workarounds described in
this section should not be considered permanent.
Most network equipment today supports IPv6 but it is by far not
ubiquitously supported in NOC backend solutions (HW/SW), especially
not in the product space for enterprises. Even when it is supported,
there are often additional limitations or issues using it in a dual
stack setup or the operator mandates for simplicity single stack for
all operations. For these reasons an IPv4 only management plane is
still required and common practice in many enterprises. Without the
desire to leverage the GACP, this required and common practice is not
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a problem for those enterprises even when they run dual stack in the
network. We discuss these workarounds here because it is a short
term deployment challenge specific to the operations of a GACP.
To connect IPv4 only management plane devices/applications with a
GACP, some form of IP/ICMP translation of packets IPv4<->IPv6 is
necessary. The basic mechanisms for this are defined in SIIT
([RFC7915]). There are multiple solutions using this mechanism. To
understand the possible solutions, we consider the requirements:
1. NMS hosts need to be able to initiate connections to any GACP
device for management purposes. Examples include provisioning
via Netconf/(SSH), SNMP poll operations or just diagnostics via
SSH connections from operators. Every GACP device/function that
needs to be reachable from NMS hosts needs to have a separate
IPv4 address.
2. GACP devices need to be able to initiate connections to NMS hosts
for example to initiate NTP or radius/diameter connections, send
syslog or SNMP trap or initiate Netconf Call Home connections
after bootstrap. Every NMS host needs to have a separate IPv6
address reachable from the GACP. When connections from GACP
devices are made to NMS hosts, the IPv4 source address of these
connections as seen by the NMS Host must also be unique per GACP
device and the same address as in (1) to maintain the same
addressing simplicity as in a native IPv4 deployment. For
example in syslog, the source-IP address of a logging device is
used to identify it, and if the device shows problems, an
operator might want to SSH into the device to diagnose it.
Because of these requirements, the necessary and sufficient set of
solutions are those that provide 1:1 mapping of IPv6 GACP addresses
into IPv4 space and 1:1 mapping of IPv4 NMS host space into IPv6 (for
use in the GACP). This means that stateless SIIT based solutions are
sufficient and preferred.
Note that GACP devices may use multiple IPv6 addresses in the GACP.
For example, [I-D.ietf-anima-autonomic-control-plane] section 6.10
defines multiple useful addressing sub-schemes supporting this
option. All those addresses may then need to be reachable through
the IPv6/IPv4 address translation.
The need to allocate for every GACP device one or multiple IPv4
addresses should not be a problem if - as we assume - the NMS hosts
can use private IPv4 address space ([RFC1918]). Nevertheless even
with RFC1918 address space it is important that the GACP IPv6
addresses can efficiently be mapped into IPv4 address space without
too much waste.
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The currently most flexible mapping scheme to achieve this is
[RFC7757] because it allows configured IPv4 <-> IPv6 prefix mapping.
Assume the GACP uses the ACP "Zone Addressing" Sub-Scheme and there
are 3 registrars. In the Zone Addressing Sub-Scheme, there is for
each registrar a constant /112 prefix for which in RFC7757 an EAM
(Explicit Address Mapping) into a /16 (e.g.: RFC1918) prefix into
IPv4 can be configured. Within the registrars /112 prefix, Device-
Numbers for devices are sequentially assigned: with V-bit effectively
two numbers are assigned per GACP device. This also means that if
IPv4 address space is even more constrained, and it is known that a
registrar will never need the full /15 extent of Device-Numbers, then
a longer than /112 prefix can be configured into the EAM to use less
IPv4 space.
When using the ACP "Vlong Addressing" Sub-Scheme, it is unlikely that
one wants or need to translate the full /8 or /16 bits of addressing
space per GACP device into IPv4. In this case, the EAM rules of
dropping trailing bits can be used to map only N bits of the V-bits
into IPv4. This does imply though that only V-addresses that differ
in those high-order N V-bits can be distinguished on the IPv4 side.
Likewise, the IPv4 address space used for NMS hosts can easily be
mapped into an address prefix assigned to a GACP connect interface.
A full specification of a solution to perform SIIT in conjunction
with GACP connect following the considerations below is outside the
scope of this document.
To be in compliance with security expectations, SIIT has to happen on
the GACP edge device itself so that GACP security considerations can
be taken into account. E.g.: that IPv4 only NMS hosts can be dealt
with exactly like IPv6 hosts connected to a GACP connect interface.
Note that prior solutions such as NAT64 ([RFC6146]) may equally be
useable to translate between GACP IPv6 address space and NMS Hosts
IPv4 address space, and that as workarounds this can also be done on
non GACP Edge Devices connected to a GACP connect interface. The
details vary depending on implementation because the options to
configure address mappings vary widely. Outside of EAM, there are no
standardized solutions that allow for mapping of prefixes, so it will
most likely be necessary to explicitly map every individual (/128)
GACP device address to an IPv4 address. Such an approach should use
automation/scripting where these address translation entries are
created dynamically whenever a GACP device is enrolled or first
connected to the GACP network.
Overall, the use of NAT is especially subject to the ROI (Return On
Investment) considerations, but the methods described here may not be
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too different from the same problems encountered totally independent
of GACP when some parts of the network are to introduce IPv6 but NMS
hosts are not (yet) upgradeable.
2.1.5. Path Selection Policies
As mentioned above, a GACP is not expected to have high performance
because its primary goal is connectivity and security, and for
existing network device platforms this often means that it is a lot
more effort to implement that additional connectivity with hardware
acceleration than without - especially because of the desire to
support full encryption across the GACP to achieve the desired
security.
Some of these issues may go away in the future with further adoption
of a GACP and network device designs that better tender to the needs
of a separate OAM plane, but it is wise to plan for even long-term
designs of the solution that does NOT depend on high-performance of
the GACP. This is opposite to the expectation that future NMS hosts
will have IPv6, so that any considerations for IPv4/NAT in this
solution are temporary.
To solve the expected performance limitations of the GACP, we do
expect to have the above describe dual-connectivity via both GACP and
data-plane between NOC application devices and devices with GACP.
The GACP connectivity is expected to always be there (as soon as a
device is enrolled), but the data-plane connectivity is only present
under normal operations but will not be present during e.g. early
stages of device bootstrap, failures, provisioning mistakes or during
network configuration changes.
The desired policy is therefore as follows: In the absence of further
security considerations (see below), traffic between NMS hosts and
GACP devices should prefer data-plane connectivity and resort only to
using the GACP when necessary, unless it is an operation known to be
so much tied to the cases where the GACP is necessary that it makes
no sense to try using the data-plane. An example are SSH connections
from the NOC into a network device to troubleshoot network
connectivity. This could easily always rely on the GACP. Likewise,
if an NMS host is known to transmit large amounts of data, and it
uses the GACP, then its performance need to be controlled so that it
will not overload the GACP performance. Typical examples of this are
software downloads.
There is a wide range of methods to build up these policies. We
describe a few:
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Ideally, a NOC system would learn and keep track of all addresses of
a device (GACP and the various data-plane addresses). Every action
of the NOC system would indicate via a "path-policy" what type of
connection it needs (e.g. only data-plane, GACP-only, default to
data-plane, fallback to GACP,...). A connection policy manager would
then build connection to the target using the right address(es).
Shorter term, a common practice is to identify different paths to a
device via different names (e.g. loopback vs. interface addresses).
This approach can be expanded to GACP uses, whether it uses NOC
system local names or DNS. We describe example schemes using DNS:
DNS can be used to set up names for the same network devices but with
different addresses assigned: One name (name.noc.example.com) with
only the data-plane address(es) (IPv4 and/or IPv6) to be used for
probing connectivity or performing routine software downloads that
may stall/fail when there are connectivity issues. One name (name-
acp.noc.example.com) with only the GACP reachable address of the
device for troubleshooting and probing/discovery that is desired to
always only use the GACP. One name with data-plane and GACP
addresses (name-both.noc.example.com).
Traffic policing and/or shaping at the GACP edge in the NOC can be
used to throttle applications such as software download into the
GACP.
Using different names mapping to different (subset of) addresses can
be difficult to set up and maintain, especially also because data-
plane addresses may change due to reconfiguration or relocation of
devices. The name based approach alone can also not well support
policies for existing applications and long-lived flows to
automatically switch between ACP and data-plane in the face of data-
plane failure and recovery. A solution would be GACP node host
transport stacks supporting the following requirements:
1. Only the GACP addresses of the responder must be required by the
initiator for the initial setup of a connection/flow across the
GACP.
2. Responder and Initiator must be able to exchange their data-plane
addresses through the GACP, and then - if needed by policy -
build an additional flow across the data-plane.
3. For unmodified application, the following policies should be
configurable on at least a per-application basis for its TCP
connections with GACP peers:
Fallback (to GACP): An additional data-plane flow is built and
used exclusively to send data whenever the data-plane is
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operational. When it can not be built during connection setup
or when it fails later, traffic is sent across the GACP flow.
This could be a default-policy for most OAM applications using
the GACP.
>Suspend/Fail: Like the Fallback policy, except that traffic
will not use the GACP flow but will be suspended until a data-
plane flow is operational or until a policy configurable
timeout indicates a connection failure to the application.
This policy would be appropriate for large volume background/
scavenger class OAM application/connections such as firmware
downloads or telemetry/diagnostic uploads - which would
otherwise easily overrun performance limited GACP
implementations.
>GACP (only): No additional data-plane flow is built, traffic is
only sent via the GACP flow. This can just be a TCP
connection. This policy would be most appropriate for OAM
operations known to change the data plane in a way that could
impact (at least temporarily) connectivity through it.
4. In the presence of responders or initiators not supporting these
host stack functions, the Fallback and GACP policies must result
in a TCP connection across the GACP. For Suspend/Fail, presence
of TCP-only peers should result in failure during connection
setup.
5. In case of Fallback and Suspend/Fail, a failed data-plane
connection should automatically be rebuilt when the data-plane
recovers, including the case that the data-plane address of one
(or both) side(s) may have changed - for example because of
reconfiguration or device repositioning.
6. Additional data-plane flows created by these host transport stack
functions must be end-to-end authenticated by it with the GACP
domain credentials and encrypted. This maintains the expectation
that connections from GACP addresses to GACP addresses are
authenticated/encrypted. This may be skipped if the application
already provides for end-to-end encryption.
7. For enhanced applications, the host stack may support application
control to select the policy on a per-connection basis, or even
more explicit control for building of the flows and which flow
should pass traffic.
Protocols like MPTCP (Multipath TCP -see [RFC6824]) and SCTP
([RFC4960]) can already support part of these requirements. MPTCP
for example supports signaling of addresses in a TCP backward
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compatible fashion, establishment of additional flows (called
subflows in MPTCP) and having primary and fallback subflows via
MP_PRIO signalling. The details if or how MPTCP, SCTP and/or other
approaches potentially with extensions and/or (shim) layers on top of
them can best provide a complete solution for the above requirements
is subject to further work outside the scope of this document.
2.1.6. Autonomic NOC Device/Applications
Setting up connectivity between the NOC and autonomic devices when
the NOC device itself is non-autonomic is as mentioned in the
beginning a security issue. It also results as shown in the previous
paragraphs in a range of connectivity considerations, some of which
may be quite undesirable or complex to operationalize.
Making NMS hosts autonomic and having them participate in the GACP is
therefore not only a highly desirable solution to the security
issues, but can also provide a likely easier operationalization of
the GACP because it minimizes NOC-special edge considerations - the
GACP is simply built all the way automatically, even inside the NOC
and only authorized and authenticate NOC devices/applications will
have access to it.
Supporting the ACP according to
[I-D.ietf-anima-autonomic-control-plane] all the way into an
application device requires implementing the following aspects in it:
AN bootstrap/enrollment mechanisms, the secure channel for the ACP
and at least the host side of IPv6 routing setup for the ACP.
Minimally this could all be implemented as an application and be made
available to the host OS via e.g. a tap driver to make the ACP show
up as another IPv6 enabled interface.
Having said this: If the structure of NMS hosts is transformed
through virtualization anyhow, then it may be considered equally
secure and appropriate to construct (physical) NMS host system by
combining a virtual GACP enabled router with non-GACP enabled NOC-
application VMs via a hypervisor, leveraging the configuration
options described in the previous sections but just virtualizing
them.
2.1.7. Encryption of data-plane connections
When combining GACP and data-plane connectivity for availability and
performance reasons, this too has an impact on security: When using
the GACP, the traffic will be mostly encryption protected, especially
when considering the above described use of application devices with
GACP. If instead the data-plane is used, then this is not the case
anymore unless it is done by the application.
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The simplest solution for this problem exists when using GACP capable
NMS hosts, because in that case the communicating GACP capable NMS
host and the GACP network device have credentials they can mutually
trust (same GACP domain). In result, data-plane connectivity that
does support this can simply leverage TLS/DTLS
([RFC5246])/([RFC6347]) with those GACP credentials for mutual
authentication - and does not incur new key management.
If this automatic security benefit is seen as most important, but a
"full" GACP stack into the NMS host is unfeasible, then it would
still be possible to design a stripped down version of GACP
functionality for such NOC hosts that only provides enrollment of the
NOC host with the GACP cryptographic credentials but without directly
participating in the GACP encryption method. Instead, the host would
just leverage TLS/DTLS using its GACP credentials via the data-plane
with GACP network devices as well as indirectly via the GACP with the
above mentioned GACP connect into the GACP.
When using the GACP itself, TLS/DTLS for the transport layer between
NMS hosts and network device is somewhat of a double price to pay
(GACP also encrypts) and could potentially be optimized away, but
given the assumed lower performance of the GACP, it seems that this
is an unnecessary optimization.
2.1.8. Long Term Direction of the Solution
If we consider what potentially could be the most lightweight and
autonomic long term solution based on the technologies described
above, we see the following direction:
1. NMS hosts should at least support IPv6. IPv4/IPv6 NAT in the
network to enable use of a GACP is long term undesirable. Having
IPv4 only applications automatically leverage IPv6 connectivity
via host-stack translation may be an option but this has not been
investigated yet.
2. Build the GACP as a lightweight application for NMS hosts so GACP
extends all the way into the actual NMS hosts.
3. Leverage and as necessary enhance host transport stacks with
automatic multipath-connectivity GACP and data-plane as outlined
in Section 2.1.5.
4. Consider how to best map NMS host desires to underlying transport
mechanisms: With the above mentioned 3 points, not all options
are covered. Depending on the OAM, one may still want only GACP,
only data-plane, or automatically prefer one over the other and/
or use the GACP with low performance or high-performance (for
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emergency OAM such as countering DDoS). It is as of today not
clear what the simplest set of tools is to enable explicitly the
choice of desired behavior of each OAM. The use of the above
mentioned DNS and multipath mechanisms is a start, but this will
require additional work. This is likely a specific case of the
more generic scope of TAPS.
2.2. Stable Connectivity for Distributed Network/OAM
Today, many distributed protocols implement their own unique security
mechanisms.
KARP (Keying and Authentication for Routing Protocols, see [RFC6518])
has tried to start to provide common directions and therefore reduce
the re-invention of at least some of the security aspects, but it
only covers routing-protocols and it is unclear how well it is
applicable to a potentially wider range of network distributed agents
such as those performing distributed OAM. The common security of a
GACP can help in these cases.
Furthermore, GRASP ([I-D.ietf-anima-grasp]) can run on top of a GACP
as a security and transport substrate and provide common local &
remote neighbor discovery and peer negotiation mechanism, further
allowing to unifying & reuse future protocol designs.
3. Architectural Considerations
3.1. No IPv4 for GACP
The GACP is intended to be IPv6 only, and the prior explanations in
this document show that this can lead to some complexity when having
to connect IPv4 only NOC solutions, and that it will be impossible to
leverage the GACP when the OAM agents on a GACP network device do not
support IPv6. Therefore, the question was raised whether the GACP
should optionally also support IPv4.
The decision not to include IPv4 for GACP as something that is
considered in the use cases in this document is because of the
following reasons:
In SP networks that have started to support IPv6, often the next
planned step is to consider moving out IPv4 from a native transport
to just a service on the edge. There is no benefit/need for multiple
parallel transport families within the network, and standardizing on
one reduces OPEX and improves reliability. This evolution in the
data-plane makes it highly unlikely that investing development cycles
into IPv4 support for GACP will have a longer term benefit or enough
critical short-term use-cases. Support for IPv6-only for GACP is
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purely a strategic choice to focus on the known important long term
goals.
In other types of networks as well, we think that efforts to support
autonomic networking is better spent in ensuring that one address
family will be supported so all use cases will long-term work with
it, instead of duplicating effort into IPv4. Especially because
auto-addressing for the GACP with IPv4 would be more complex than in
IPv6 due to the IPv4 addressing space.
4. Security Considerations
In this section, we discuss only security considerations not covered
in the appropriate sub-sections of the solutions described.
Even though GACPs are meant to be isolated, explicit operator
misconfiguration to connect to insecure OAM equipment and/or bugs in
GACP devices may cause leakage into places where it is not expected.
Mergers/Acquisitions and other complex network reconfigurations
affecting the NOC are typical examples.
GACP addresses are ULA addresses. Using these addresses also for NOC
devices as proposed in this document is not only necessary for above
explained simple routing functionality but it is also more secure
than global IPv6 addresses. ULA addresses are not routed in the
global Internet and will therefore be subject to more filtering even
in places where specific ULA addresses are being used. Packets are
therefore less likely to leak to be successfully injected into the
isolated GACP environment.
The random nature of a ULA prefix provides strong protection against
address collision even though there is no central assignment
authority. This is helped by the expectation that GACPs are never
expected to connect all together, but only few GACPs may ever need to
connect together, e.g. when mergers and acquisitions occur.
Note that the GACP constraints demands that only packets from
connected subnet prefixes are permitted from GACP connect interfaces,
limiting the scope of non-cryptographically secured transport to a
subnet within a NOC that instead has to rely on physical security
(only connect trusted NOC devices to it).
To help diagnose packets that unexpectedly leaked for example from
another GACP (that was meant to be deployed separately), it can be
useful to voluntarily list your own the ULA GACP prefixes on some
site(s) on the Internet and hope that other users of GACPs do the
same so that you can look up unknown ULA prefix packets seen in your
network. Note that this does not constitute registration.
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https://www.sixxs.net/tools/grh/ula/ was a site to list ULA prefixes
but it is not open for new listings anymore since the mid of 2017.
The authors are not aware of other active Internet sites to list ULA
use.
Note that there is a provision in [RFC4193] for non-locally assigned
address space (L bit = 0), but there is no existing standardization
for this, so these ULA prefixes must not be used.
According to [RFC4193] section 4.4, PTR records for ULA addresses
should not be installed into the global DNS (no guaranteed
ownership). Hence also the need to rely on voluntary lists (and in
prior paragraph) to make the use of an ULA prefix globally known.
Nevertheless, some legacy OAM applications running across the GACP
may rely on reverse DNS lookup for authentication of requests (e.g.:
TFTP for download of network firmware/config/software). Operators
may therefore need to use a private DNS setup for the GACP ULA
addresses. This is the same setup that would be necessary for using
RFC1918 addresses in DNS. See for example [RFC1918] section 5, last
paragraph. In [RFC6950] section 4, these setups are discussed in
more detail.
Any current and future protocols must rely on secure end-to-end
communications (TLS/DTLS) and identification and authentication via
the certificates assigned to both ends. This is enabled by the
cryptographic credentials mechanisms of the GACP.
If DNS and especially reverse DNS are set up, then it should be set
up in an automated fashion when the GACP address for devices are
assigned. In the case of the ACP, DNS resource record creation can
be linked to the autonomic registrar backend so that the DNS and
reverse DNS records are actually derived from the subject name
elements of the ACP device certificates in the same way as the
autonomic devices themselves will derive their ULA addresses from
their certificates to ensure correct and consistent DNS entries.
If an operator feels that reverse DNS records are beneficial to its
own operations but that they should not be made available publically
for "security" by concealment reasons, then the case of GACP DNS
entries is probably one of the least problematic use cases for split-
DNS: The GACP DNS names are only needed for the NMS hosts intending
to use the GACP - but not network wide across the enterprise.
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5. IANA Considerations
This document requests no action by IANA.
6. Acknowledgements
This work originated from an Autonomic Networking project at cisco
Systems, which started in early 2010 including customers involved in
the design and early testing. Many people contributed to the aspects
described in this document, including in alphabetical order: BL
Balaji, Steinthor Bjarnason, Yves Herthoghs, Sebastian Meissner, Ravi
Kumar Vadapalli. The author would also like to thank Michael
Richardson, James Woodyatt and Brian Carpenter for their review and
comments. Special thanks to Sheng Jiang and Mohamed Boucadair for
their thorough review.
7. Change log [RFC Editor: Please remove]
10: Added paragraph to multipath text to better summarize the
reason why to do this.
10: Mirja: reworded multipath text to remove instructive
description how the desired functionality would map to MPTCP
features, extensions or shim layers. Describe the desired
functionality now only as requirements. Expert WGs including but
not limited to MPTCP and future documents need to define best
design/spec option.
10: BrianC: Added requirement to 'MPTCP' section for end-to-end
encryption across data plane when connection is via GACP.
09: Mirja/Yoshifumi: reworded MPTCP policy rule examples,
stack->endpoint (agnostic to where policy is implemented).
08: IESG review fixes.
* Spell check.
* https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/01908364cfc7259009603bf2b261354b0cc26913/draft-ietf-
anima-stable-connectivity/draft-ietf-anima-stable-connectivity-
08.txt
* Eric Rescorla (comments):Typos, listing ULA on internet
benefits. Other comments from Eric where addressed via commits
for other reviewers already.
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* https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/c02252710fbd7aea15aff550fb393eb36584658b/draft-ietf-
anima-stable-connectivity/draft-ietf-anima-stable-connectivity-
08.txt
* Mirja Kuehlewind (discuss) / Yoshifumi Nishida: Fixed and
Rewrote MPTCP text to be more explanatory, answering questions
raised in disucss.
* https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/14d5f9b66b8318bc160cee74ad152c0b926b4042/draft-ietf-
anima-stable-connectivity/draft-ietf-anima-stable-connectivity-
08.txt
* Matthew Miller/Alissa Cooper: syntactic nits.
* https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/9bff109281e8b3c22522c3144cbf0f13e5000498/draft-ietf-
anima-stable-connectivity/draft-ietf-anima-stable-connectivity-
08.txt
* Suresh Krishnan (comment): rewrote first paragraph of 2.1.4
(incomprehensible).
* https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/f2d8a85c2cc65ca7f823abac0f57d19c744f9b65/draft-ietf-
anima-stable-connectivity/draft-ietf-anima-stable-connectivity-
08.txt
* Alvaro Retana: Made references normative where the authors
think is is important to understand all or parts for the
mechanisms described in this document.
* Alvaro Retana: Clarified that the discussions in this document
are not specific to the ANI ACP, but instead rely primarily on
a set of design constraints for any type of autonomic inband
management network. Called this the GACP (generalized ACP).
Mayor add: explanation of those design constraints in section
1.3. Textual fixes ACP -> GACP throughout the document, but
without semantic changes.
* https://raw.githubusercontent.com/anima-wg/autonomic-control-
plane/d26df831da2953779c3b3ac41ec118cbbe43373e/draft-ietf-
anima-stable-connectivity/draft-ietf-anima-stable-connectivity-
08.txt
* Co-author organization fix.
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07: Fixed ID nits.
06: changed "split-horizon" term to "private-DNS" and reworded the
paragraph about it.
05: Integrated fixes from Brian Carpenters review. See github
draft-ietf-anima-stable-connectivity/04-brian-carpenter-review-
reply.txt. Details on semantic/structural changes:
* Folded most comments back into draft-ietf-anima-autonomic-
control-plane-09 because this stable connectivity draft was
suggesting things that are better written out and standardized
in the ACP document.
* Section on simultaneous ACP and data-plane connectivity section
reduced/rewritten because of this.
* Re-emphasized security model of ACP - ACP-connect can not
arbitrarily extend ACP routing domain.
* Re-wrote much of NMS section to be less suggestive and more
descriptive, avoiding the term NAT and referring to relevant
RFCs (SIIT etc.).
* Main additional text in IPv4 section is about explaining how we
suggest to use EAM (Explicit Address Mapping) which actuall
would well work with the Zone and Vlong Addressing Sub-Schemes
of ACP.
* Moved, but not changed section of "why no IPv4 in ACP" before
IANA considerations to make structure of document more logical.
* Refined security considerations: explained how optional ULA
prefix listing on Internet is only for diagnostic purposes.
Explained how this is useful because DNS must not be used.
Explained how split horizon DNS can be used nevertheless.
04: Integrated fixes from Mohamed Boucadairs review (thorough
textual review).
03: Integrated fixes from thorough Shepherd review (Sheng Jiang).
01: Refresh timeout. Stable document, change in author
association.
01: Refresh timeout. Stable document, no changes.
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00: Changed title/dates.
individual-02: Updated references.
individual-03: Modified ULA text to not suggest ULA-C as much
better anymore, but still mention it.
individual-02: Added explanation why no IPv4 for ACP.
individual-01: Added security section discussing the role of
address prefix selection and DNS for ACP. Title change to
emphasize focus on OAM. Expanded abstract.
individual-00: Initial version.
8. References
8.1. Normative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
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>.
[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>.
[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>.
[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>.
[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>.
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[RFC7757] Anderson, T. and A. Leiva Popper, "Explicit Address
Mappings for Stateless IP/ICMP Translation", RFC 7757,
DOI 10.17487/RFC7757, February 2016,
<https://www.rfc-editor.org/info/rfc7757>.
[RFC7915] Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
"IP/ICMP Translation Algorithm", RFC 7915,
DOI 10.17487/RFC7915, June 2016,
<https://www.rfc-editor.org/info/rfc7915>.
8.2. Informative References
[I-D.ietf-anima-autonomic-control-plane]
Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
Control Plane (ACP)", draft-ietf-anima-autonomic-control-
plane-13 (work in progress), December 2017.
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-09 (work in progress), October 2017.
[I-D.ietf-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
grasp-15 (work in progress), July 2017.
[I-D.ietf-anima-reference-model]
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
Pierre, P., Liu, B., Nobre, J., and J. Strassner, "A
Reference Model for Autonomic Networking", draft-ietf-
anima-reference-model-05 (work in progress), October 2017.
[IEEE802.1Q]
International Telecommunication Union, "802.1Q-2014 - IEEE
Standard for Local and metropolitan area networks -
Bridges and Bridged Networks", 2014.
[ITUT] International Telecommunication Union, "Architecture and
specification of data communication network",
ITU-T Recommendation G.7712/Y.1703, Noevember 2001.
This is the earliest but superceeded version of the
series. See "https://www.itu.int/rec/T-REC-G.7712/en" for
current versions.
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[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[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>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/info/rfc6291>.
[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>.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, DOI 10.17487/RFC6434, December
2011, <https://www.rfc-editor.org/info/rfc6434>.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
DOI 10.17487/RFC6518, February 2012,
<https://www.rfc-editor.org/info/rfc6518>.
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in
the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013,
<https://www.rfc-editor.org/info/rfc6950>.
Authors' Addresses
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Toerless Eckert (editor)
Futurewei Technologies Inc.
2330 Central Expy
Santa Clara 95050
USA
Email: tte+ietf@cs.fau.de
Michael H. Behringer
Email: michael.h.behringer@gmail.com
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