IDR Working Group Z. Ali
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track C. Lin
Expires: 6 December 2026 New H3C Technologies
Y. Liu
China Mobile
R. Chen
ZTE Corporation
4 June 2026
SRv6 Policy SID List Optimization Advertisement
draft-ali-idr-bgp-ls-sr-policy-sl-opt-distribution-00
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 BGP-LS extension to
indicate whether the endpoint's node SID is included or excluded in
installing SID list(s) of the Candidate Path (CP) of an SRv6 policy.
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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This Internet-Draft will expire on 6 December 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
and restrictions with respect to this document. Code Components
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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 BGP Extensions . . . . . . . . . . . . . . . . . 3
5. Cross WG Information . . . . . . . . . . . . . . . . . . . . 4
5.1. Link to Spring WG . . . . . . . . . . . . . . . . . . . . 4
5.2. Interaction with SRV6ops Recommendations . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
9.1. Normative References . . . . . . . . . . . . . . . . . . 4
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 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). [RFC9857] defines a mechanism to
collect the Segment Routing Policy information that is locally
available in a node and advertise it into BGP Link-State (BGP-LS)
updates.
The SRv6 policy 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
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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.ietf-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 BGP-LS extension to indicate whether the
endpoint's node SID is included or excluded in installing SID list(s)
of the Candidate Path (CP) of an 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
Headend node: Packet flows are steered into an SR Policy on a node
where it is instantiated called a headend node [RFC9256].
SR: Segment Routing.
SID: Segment Identifier.
SRv6: Segment Routing over IPv6 data plane.
4. Overview of BGP Extensions
IFN-flag (Install Final Node-sid) in the SR Candidate Path State TLV
specified in [RFC9857] is proposed to indicate whether the endpoint
node SID is included or excluded in installing SID list(s) of the
Candidate Path (CP). The flag is applicable only to SR policies with
SRv6 data plane. The flag MUST NOT be set and MUST be ignored for SR
policies with SR-MPLS data plane.
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IFN (Install Final Node-sid) - 1 bit (Bit Position TBD1):
* If set to 1 indictaes the endpoint node SID is installed when
installing the SRv6 Policy SID list(s) used to carry the data
traffic.
* If set to 0 indictaes the endpoint node SID is excluded when
installing the SRv6 Policy SID list(s) used to carry the data
traffic.
5. Cross WG Information
5.1. Link to Spring WG
This document implements the procedures in Section 4 of
[I-D.ietf-spring-srv6-policy-sid-list-opt] via BGP. This spring
feature requires both this document and [RFC9857] to be implemented.
5.2. Interaction with SRV6ops Recommendations
For SRv6 deployment recommendations of the BGP-LS extension
implemented by this document, please refer to Section 5.2 of
[I-D.ietf-srv6ops-srv6-deployment].
6. Security Considerations
TBA
7. IANA Considerations
TBA
8. Acknowledgments
The authors would like to thank Ketan Talaulikar for the review
comments.
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>.
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[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>.
[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>.
[RFC9857] Previdi, S., Talaulikar, K., Ed., Dong, J., Gredler, H.,
and J. Tantsura, "Advertisement of Segment Routing
Policies Using BGP - Link State", RFC 9857,
DOI 10.17487/RFC9857, October 2025,
<https://www.rfc-editor.org/info/rfc9857>.
9.2. Informative References
[I-D.ietf-spring-srv6-mpls-interworking]
Agrawal, S., Filsfils, C., Voyer, D., Dawra, G., Li, Z.,
and S. Hegde, "SRv6 and MPLS interworking", Work in
Progress, Internet-Draft, draft-ietf-spring-srv6-mpls-
interworking-02, 7 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-mpls-interworking-02>.
[I-D.ietf-spring-srv6-policy-sid-list-opt]
Ali, Z., Lin, C., Liu, Y., Chen, R., and C. Li, "SRv6
Policy SID List Optimization", Work in Progress, Internet-
Draft, draft-ietf-spring-srv6-policy-sid-list-opt-00, 25
November 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-spring-srv6-policy-sid-list-opt-00>.
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[I-D.ietf-srv6ops-srv6-deployment]
McBride, M., Liu, Y., Li, Z., Mehmet, D., Erdogan, E.,
Mishra, G. S., and J. Horn, "SRv6 Deployment Options",
Work in Progress, Internet-Draft, draft-ietf-srv6ops-srv6-
deployment-02, 25 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-srv6ops-
srv6-deployment-02>.
Contributors
Rajesh M Venkateswaran
Cisco Systems, Inc.
Email: rmelarco@cisco.com
Yuanxiang Qiu
New H3C Technologies
Email: qiuyuanxiang@h3c.com
Cheng Li
Huawei Technologies
Email: c.l@huawei.com
Authors' Addresses
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
Ran Chen
ZTE Corporation
Email: chen.ran@zte.com.cn
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