Path Computation Element Communication Protocol (PCEP) extensions for SRv6 Policy SID List Optimization
draft-ali-pce-srv6-policy-sid-list-optimization-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Zafar Ali , Rajesh M Venkateswaran , Samuel Sidor , Cheng Li | ||
| Last updated | 2024-11-04 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-ali-pce-srv6-policy-sid-list-optimization-01
PCE Working Group Z. Ali
Internet-Draft R. Venkateswaran
Intended status: Standards Track S. Sidor
Expires: 8 May 2025 Cisco
C. Li
Huawei Technologies
4 November 2024
Path Computation Element Communication Protocol (PCEP) extensions for
SRv6 Policy SID List Optimization
draft-ali-pce-srv6-policy-sid-list-optimization-01
Abstract
In some use cases, an SRv6 policy's SID list ends with the policy
endpoint's node SID, and the traffic steered (over policy) already
ensures that it is taken to the policy endpoint. In such cases, the
SID list can be optimized by excluding the endpoint Node SID when
installing the policy. This draft specifies a PCEP extension to
indicate whether the endpoint's node SID needs to be included or
excluded when installing the SRv6 Policy.
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.
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
working documents as Internet-Drafts. The list of current Internet-
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 8 May 2025.
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview of PCEP Extensions . . . . . . . . . . . . . . . . . 3
4.1. New flag in SRv6-PCE-CAPABILITY sub-TLV . . . . . . . . . 4
4.2. New flag in the LSP-EXTENDED-FLAG TLV . . . . . . . . . . 4
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Backward compatibility . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Segment Routing (SR) [RFC8402] allows a node to steer a packet flow
along any path. A Segment Routing Policy (SR Policy) [RFC8402] is an
ordered list of segments that represent a source-routed policy. The
headend node is said to steer a flow into an SR Policy. The packets
steered into an SR Policy have an ordered list of segments associated
with that SR Policy written into them. Segment Routing Policy
Architecture [RFC9256] updates [RFC8402] as it details the concepts
of SR Policy and steering into an SR Policy. [RFC8986] describes the
representation and processing of this ordered list of segments for
Segment Routing over IPv6 (SRv6). [RFC9603] specifies PCEP
extensions to support SR for the IPv6 data plane.
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A PCE computes the SRv6 TE Policy SID list from the headend to the
endpoint. The computed SID list may end with the policy endpoint's
Node SID or the penultimate hop adjacency SID. If the computed SID
list ends with the policy endpoint's node SID and the overlay SID in
the steered traffic (over policy) already ensures that the traffic is
taken to the policy endpoint with the same intent, the SRv6 policy
endpoint device needs to process back-to-back local node SIDs.
Examples of overlay SID containing the local node SID are a service
SID, a binding SID for transit policies, an EPE SID, etc. From a
compression efficiency viewpoint, carrying back-to-back end-point
node SID is inefficient. The SID list in the packet can be optimized
by excluding the end-point node SID when installing the policy. End-
point node SID exclusion improves the compression efficiency and
makes packet processing more efficient for the policy endpoint.
Excluding the policy endpoint's node SID is possible in most use
cases, but not all. For example, if the SRv6 policy is used to carry
MPLS traffic, as described in [I-D.draft-agrawal-spring-srv6-mpls-
interworking], it is not possible to exclude the policy endpoint's
node SID. Specifically, the endpoint's node SID inclusion or
exclusion is a policy attribute. This draft specifies a PCEP
extension to include or exclude the node SID when installing the SRv6
Policy.
2. 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. Terminology
This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP, PCEP Peer.
SR: Segment Routing.
SID: Segment Identifier.
SRv6: Segment Routing over IPv6 data plane.
4. Overview of PCEP Extensions
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4.1. New flag in SRv6-PCE-CAPABILITY sub-TLV
I-flag (endpoint node SID Inclusion capability flag) is proposed in
the SRv6-PCE-CAPABILITY sub-TLV defined in [RFC9603]. The bit
position for the flag in the SRv6 Capability Flag Field registry is
to be defined by IANA.
I (endpoint node SID Inclusion capability flag) - 1 bit (Bit Position
TBD1):
* If set to 1, it indicates support for the I-flag in the LSP-
EXTENDED-FLAG TLV.
4.2. New flag in the LSP-EXTENDED-FLAG TLV
I-flag (endpoint node SID Inclusion flag) is proposed in the LSP-
EXTENDED-FLAG TLV introduced [RFC9357]. The bit position for the
flag is to be defined by IANA.
I (endpoint node SID Inclusion) - 1 bit (Bit Position TBD2):
* If set to 1, the endpoint node SID MUST be included when
installing the SR Policy SID list(s) used to carry the data
traffic.
* If set to 0, the endpoint node SID MUST NOT be included when
installing the SR Policy SID list(s) used to carry the data
traffic.
5. Operation
A PCEP speaker indicates its ability to support I-flag in LSP-
EXTENDED-FLAG TLV during the PCEP initialization phase by setting the
I-flag in the SRv6-PCE-CAPABILITY sub-TLV in the Open message.
A PCEP peer indicates the inclusion or exclusion of the endpoint's
Node SID in I-flag in LSP-EXTENDED-FLAG TLV.
A PCEP peer MUST NOT set the I-flag flag if capability was not
advertised by both peers.
If the PCEP peers are capable of supporting the I-flag and the I-flag
in the LSP-EXTENDED-FLAG TLV is set, the PCC MUST include the
endpoint node SID when installing the Policy sid list(s) used to
carry data traffic.
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If the PCEP peers are capable of supporting the I-flag and the I-flag
in the LSP-EXTENDED-FLAG TLV is not set, the PCC MUST NOT include the
endpoint node SID when installing the Policy sid list(s) used to
carry data traffic.
I-flag value in LSP-EXTENDED-FLAG TLV MUST NOT change for a given SR
Policy Candidate Path during its lifetime.
Local policy at PCC MAY override the I-flag.
PCE ignores the I-flag received from the PCC when computing the path
and computes the SRv6 TE Policy SID list from the headend to the
endpoint. PCE MAY use the I-flag value for debugging purposes.
6. Backward compatibility
If at least one PCEP peer is not capable of supporting the I-flag,
the endpoint Node SID inclusion/exclusion SHOULD be set based on
local policy at the PCC.
7. Security Considerations
TBA
8. IANA Considerations
TBA
9. References
9.1. 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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[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>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[RFC9357] Xiong, Q., "Label Switched Path (LSP) Object Flag
Extension for Stateful PCE", RFC 9357,
DOI 10.17487/RFC9357, February 2023,
<https://www.rfc-editor.org/info/rfc9357>.
[RFC9603] Li, C., Ed., Kaladharan, P., Sivabalan, S., Koldychev, M.,
and Y. Zhu, "Path Computation Element Communication
Protocol (PCEP) Extensions for IPv6 Segment Routing",
RFC 9603, DOI 10.17487/RFC9603, July 2024,
<https://www.rfc-editor.org/info/rfc9603>.
9.2. Informative References
Appendix A. Acknowledgements
The authors would like to thank Ketan Talaulikar for the review
comments.
Authors' Addresses
Zafar Ali
Cisco
Email: zali@cisco.com
Rajesh M Venkateswaran
Cisco
Email: melarco@cisco.com
Samuel Sidor
Cisco
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Email: ssidor@cisco.com
Cheng Li
Huawei Technologies
Email: c.l@huawei.com
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