Internet DRAFT - draft-ietf-pce-lsp-control-request
draft-ietf-pce-lsp-control-request
PCE Working Group A. Raghuram
Internet-Draft A. Goddard
Intended status: Standards Track AT&T
Expires: April 15, 2020 J. Karthik
S. Sivabalan
Cisco Systems, Inc.
M. Negi
Huawei Technologies
October 13, 2019
Ability for a Stateful Path Computation Element (PCE) to request and
obtain control of a Label Switched Path (LSP)
draft-ietf-pce-lsp-control-request-11
Abstract
A Stateful Path Computation Element (PCE) retains information about
the placement of Multiprotocol Label Switching (MPLS) Traffic
Engineering Label Switched Paths (TE LSPs). When a PCE has stateful
control over LSPs it may send indications to LSP head-ends to modify
the attributes (especially the paths) of the LSPs. A Path
Computation Client (PCC) that has set up LSPs under local
configuration may delegate control of those LSPs to a stateful PCE.
There are use-cases in which a stateful PCE may wish to obtain
control of locally configured LSPs of which it is aware but that have
not been delegated to the PCE.
This document describes an extension to the Path Computation Element
communication Protocol (PCEP) to enable a PCE to make requests for
such control.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on April 15, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. LSP Control Request Flag . . . . . . . . . . . . . . . . . . 4
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
5.1. Huawei's Proof of Concept based on ONOS . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. SRP Object Flags . . . . . . . . . . . . . . . . . . . . 8
8. Manageability Considerations . . . . . . . . . . . . . . . . 8
8.1. Control of Function and Policy . . . . . . . . . . . . . 8
8.2. Information and Data Models . . . . . . . . . . . . . . . 8
8.3. Liveness Detection and Monitoring . . . . . . . . . . . . 8
8.4. Verify Correct Operations . . . . . . . . . . . . . . . . 8
8.5. Requirements On Other Protocols . . . . . . . . . . . . . 9
8.6. Impact On Network Operations . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Stateful Path Computation Element (PCE) communication Protocol (PCEP)
extensions [RFC8231] specifies a set of extensions to PCEP [RFC5440]
to enable stateful control of Traffic Engineering Label Switched
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Paths (TE LSPs) between and across PCEP sessions in compliance with
[RFC4657]. It includes mechanisms to synchronize LSP state between
Path Computation Clients (PCCs) and PCEs, delegate control of LSPs to
PCE, and PCE-control of timing and sequence of path computations
within and across PCEP sessions. The stateful PCEP defines the
following two useful network operations:
o Delegation: As per [RFC8051], an operation to grant a PCE
temporary rights to modify a subset of LSP parameters on one or
more LSPs of a PCC. LSPs are delegated from a PCC to a PCE and
are referred to as "delegated" LSPs.
o Revocation: As per [RFC8231], an operation performed by a PCC on a
previously delegated LSP. Revocation revokes the rights granted
to the PCE in the delegation operation.
For Redundant Stateful PCEs (section 5.7.4. of [RFC8231]), during a
PCE failure, one of the redundant PCE might want to request to take
control over an LSP. The redundant PCEs may use a local policy or a
proprietary election mechanism to decide which PCE would take
control. In this case, a mechanism is needed for a stateful PCE to
request control of one or more LSPs from a PCC, so that a newly
elected primary PCE can request to take over control.
In case of virtualized PCEs (vPCEs) running in virtual network
function (VNF) mode, as the computation load in the network
increases, a new instance of vPCE could be instantiated to balance
the current load. The PCEs could use a proprietary algorithm to
decide which LSPs to be assigned to the new vPCE. Thus, having a
mechanism for the PCE to request control of some LSPs is needed.
In some deployments, the operator would like to use stateful PCE for
global optimization algorithms but would still like to keep the
control of the LSP at the PCC. In such cases, a stateful PCE could
request to take control during the global optimization and return the
delegation once done.
Note that [RFC8231] specifies a mechanism for a PCC to delegate an
orphaned LSP to another PCE. The mechanism defined in this document
can be used in conjunction to [RFC8231]. Ultimately, it is the PCC
that decides which PCE to delegate the orphaned LSP to.
This specification provides a simple extension: by using it a PCE can
request control of one or more LSPs from any PCC over the stateful
PCEP session. The procedures for granting and relinquishing control
of the LSPs are specified in accordance with the specification
[RFC8231] unless explicitly set aside in this document.
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2. Terminology
This document uses the following terms defined in [RFC5440]:
PCC: Path Computation Client.
PCE: Path Computation Element.
PCEP: Path Computation Element communication Protocol.
This document uses the following terms defined in [RFC8231]:
PCRpt: Path Computation State Report message.
PCUpd: Path Computation Update Request message.
PLSP-ID: A PCEP-specific identifier for the LSP.
SRP: Stateful PCE Request Parameters.
Readers of this document are expected to have some familiarity with
[RFC8231].
2.1. Requirements Language
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. LSP Control Request Flag
The Stateful PCE Request Parameters (SRP) object is defined in
Section 7.2 of [RFC8231] and it includes a Flags field.
A new flag, the "LSP-Control Request Flag" (C) - TBD, is introduced
in the SRP object. On a PCUpd message, a PCE sets the C Flag to 1 to
indicate that it wishes to gain control of LSPs. The LSPs are
identified by the PLSP-ID in the LSP object following the SRP object.
A PLSP-ID of value other than 0 and 0xFFFFF is used to identify the
LSP for which the PCE requests control. The PLSP-ID value of 0
indicates that the PCE is requesting control of all LSPs originating
from the PCC that it wishes to delegate. The C Flag has no meaning
in other PCEP messages that carry SRP objects and for which the C
flag MUST be set to 0 on transmission and MUST be ignored on receipt.
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4. Operation
During normal operation, a PCC that wishes to delegate the control of
an LSP sets the D Flag (delegate, Section 7.3 of [RFC8231]) to 1 in
all PCRpt messages pertaining to the LSP. The PCE confirms the
delegation by setting D Flag to 1 in all PCUpd messages pertaining to
the LSP. The PCC revokes the control of the LSP from the PCE by
setting D Flag to 0 in PCRpt messages pertaining to the LSP. If the
PCE wishes to relinquish the control of the LSP, it sets D Flag to 0
in all PCUpd messages pertaining to the LSP.
If a PCE wishes to gain control over an LSP, it sends a PCUpd message
with C Flag set to 1 in SRP object. The LSP for which the PCE
requests control is identified by the PLSP-ID in the associated LSP
object. The PLSP-ID of 0 indicates that the PCE wants control over
all LSPs originating from the PCC. An implementation of this feature
needs to make sure to check for the LSP control feature (C flag set
to 1) before any check for PLSP-ID (as prescribed in [RFC8231]). The
D Flag and C Flag are mutually exclusive in a PCUpd message. The PCE
MUST NOT send a control request for the LSP which is already
delegated to the PCE, i.e. if the D Flag is set in the PCUpd message,
then the C Flag MUST NOT be set. If a PCC receives a PCUpd message
with D Flag set in the LSP object (i.e. LSP is already delegated)
and the C Flag is also set (i.e. PCE is making a control request),
the PCC MUST ignore the C Flag. A PCC can decide to delegate the
control of the LSP at its own discretion. If the PCC grants or
denies the control, it sends a PCRpt message with D Flag set to 1 and
0 respectively in accordance with stateful PCEP [RFC8231]. If the
PCC does not grant the control, it MAY choose to not respond, and the
PCE MAY choose to retry requesting the control preferably using
exponentially increasing timer. Note that, if the PCUpd message with
C Flag set is received for a currently non-delegated LSP (for which
the PCE is requesting delegation), this MUST NOT trigger the error
handling as specified in [RFC8231] (a PCErr with Error-type=19
(Invalid Operation) and error-value 1 (Attempted LSP Update Request
for a non-delegated LSP)).
As per [RFC8231], a PCC cannot delegate an LSP to more than one PCE
at any time. If a PCE requests control of an LSP that has already
been delegated by the PCC to another PCE, the PCC MAY ignore the
request, or MAY revoke the delegation to the first PCE before
delegating it to the second. This choice is a matter of local
policy.
It should be noted that a legacy implementation of PCC that does not
support this extension would receive an LSP control request: PCUpd
message with C flag set and D flag (delegate) unset, it would ignore
the C flag and trigger the error condition for the D flag as
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specified in [RFC8231] (a PCErr with Error-type=19 (Invalid
Operation) and error-value 1 (Attempted LSP Update Request for a non-
delegated LSP)). Further, in case of PLSP-ID of 0, the error
condition as specified in [RFC8231] (a PCErr with Error-type=19
(Invalid Operation) and error-value 3 (Attempted LSP Update Request
for an LSP identified by an unknown PSP-ID)) would be triggered.
[RFC8281] describes the setup, maintenance and teardown of PCE-
initiated LSPs under the stateful PCE model. It also specifies how a
PCE may obtain control over an orphaned LSP that was PCE-initiated.
A PCE implementation can apply the mechanism described in this
document in conjunction with those in [RFC8281].
5. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to RFC 7942.]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
5.1. Huawei's Proof of Concept based on ONOS
The PCE function was developed in the ONOS open source platform.
This extension was implemented on a private version as a proof of
concept to enable multi-instance support.
o Organization: Huawei
o Implementation: Huawei's PoC based on ONOS
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o Description: PCEP as a southbound plugin was added to ONOS. To
support multi-instance ONOS deployment in a cluster, this
extension in PCEP is used. Refer
https://wiki.onosproject.org/display/ONOS/PCEP+Protocol
o Maturity Level: Prototype
o Coverage: Full
o Contact: satishk@huawei.com
6. Security Considerations
The security considerations listed in [RFC8231] and [RFC8281] apply
to this document as well. However, this document also introduces a
new attack vector. An attacker may flood the PCC with request to
delegate all of its LSPs at a rate which exceeds the PCC's ability to
process them, either by spoofing messages or by compromising the PCE
itself. The PCC SHOULD be configured with a threshold rate for the
delegation requests received from the PCE. If the threshold is
reached, it is RECOMMENDED to log the issue.
A PCC is the ultimate arbiter of delegation. As per [RFC8231], a
local policy at PCC is used to influence the delegation. A PCC can
also revoke the delegation at any time. A PCC need not blindly trust
the control requests and SHOULD take local policy and other factors
into consideration before honoring the request.
Note that, a PCE may not be sure if a PCC supports this feature. A
PCE would try sending a control request to a 'legacy' PCC, which
would in turn respond with an error as described in Section 4. So a
PCE would learn this fact only when it wants to take control over an
LSP. A PCE might also be susceptible to a downgrade attacks by
falsifying the error condition.
As per [RFC8231], it is RECOMMENDED that these PCEP extensions only
be activated on authenticated and encrypted sessions across PCEs and
PCCs belonging to the same administrative authority, using Transport
Layer Security (TLS) [RFC8253], as per the recommendations and best
current practices in BCP 195 [RFC7525] (unless explicitly excluded in
[RFC8253]).
7. IANA Considerations
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7.1. SRP Object Flags
IANA maintains a registry called the "Path Computation Element
Protocol (PCEP) Numbers" registry. It contains a subregistry called
the "SRP Object Flag Field" registry. This document requests IANA to
allocate following code point in the "SRP Object Flag Field"
subregistry.
Bit Description Reference
TBD LSP-Control Request Flag This document
8. Manageability Considerations
All manageability requirements and considerations listed in [RFC5440]
and [RFC8231] apply to PCEP protocol extensions defined in this
document. In addition, requirements and considerations listed in
this section apply.
8.1. Control of Function and Policy
A PCC implementation SHOULD allow the operator to configure the
policy based on which it honors the request to control the LSPs.
This includes the handling of the case where an LSP control request
is received for an LSP that is currently delegated to some other PCE.
A PCC implementation SHOULD also allow the operator to configure the
threshold rate based on which it accepts the delegation requests from
the PCE. Further, the operator MAY be allowed to trigger the LSP
control request for a particular LSP at the PCE. A PCE
implementation SHOULD also allow the operator to configure an
exponentially increasing timer to retry the control requests for
which the PCE did not get a response.
8.2. Information and Data Models
The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to
include mechanism to trigger the LSP control request.
8.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
8.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440] and [RFC8231].
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8.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
8.6. Impact On Network Operations
Mechanisms defined in [RFC5440] and [RFC8231] also apply to PCEP
extensions defined in this document. Further, the mechanism
described in this document can help the operator to request control
of the LSPs at a particular PCE.
9. Acknowledgements
Thanks to Jonathan Hardwick to remind the authors to not use
suggested values in IANA section.
Thanks to Adrian Farrel, Haomian Zheng and Tomonori Takeda for their
valuable comments.
Thanks to Shawn M. Emery for security directorate's review.
Thanks to Francesca Palombini for GENART review.
Thanks to Benjamin Kaduk, Martin Vigoureux, Alvaro Retana, and Barry
Leiba for IESG reviews.
10. References
10.1. Normative References
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[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>.
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[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
10.2. Informative References
[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <https://www.rfc-editor.org/info/rfc4657>.
[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>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep-
yang-12 (work in progress), July 2019.
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Appendix A. Contributor Addresses
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: dhruv.ietf@gmail.com
Jon Parker
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
EMail: jdparker@cisco.com
Chaitanya Yadlapalli
AT&T
200 S Laurel Aevenue
Middletown NJ 07748
USA
EMail: cy098d@att.com
Authors' Addresses
Aswatnarayan Raghuram
AT&T
200 S Laurel Aevenue
Middletown, NJ 07748
USA
EMail: ar2521@att.com
Al Goddard
AT&T
200 S Laurel Aevenue
Middletown, NJ 07748
USA
EMail: ag6941@att.com
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Jay Karthik
Cisco Systems, Inc.
125 High Street
Boston, Massachusetts 02110
USA
EMail: jakarthi@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
EMail: msiva@cisco.com
Mahendra Singh Negi
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: mahend.ietf@gmail.com
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