



IDR                                                               C. Lin
Internet-Draft                                      New H3C Technologies
Intended status: Standards Track                                W. Cheng
Expires: 29 October 2026                                    China Mobile
                                                                  Y. Liu
                                                                     ZTE
                                                           K. Talaulikar
                                                           Cisco Systems
                                                                 M. Chen
                                                    New H3C Technologies
                                                           27 April 2026


          BGP SR Policy Extensions for Segment List Identifier
                 draft-ietf-idr-sr-policy-seglist-id-09

Abstract

   Segment Routing (SR) is a source routing paradigm that explicitly
   indicates the forwarding path for packets at the ingress node.  An SR
   Policy is a set of candidate paths, each consisting of one or more
   segment lists.  This document defines extensions to BGP SR Policy to
   specify the identifier of a segment list.

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 29 October 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
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Segment List Identifier in SR Policy  . . . . . . . . . . . .   3
     2.1.  Segment List ID Sub-TLV . . . . . . . . . . . . . . . . .   5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
     4.1.  New H3C Technologies  . . . . . . . . . . . . . . . . . .   7
     4.2.  ZTE Corp  . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Cross WG Information . . . . . . . . . . . . . . . .  10
     A.1.  Spring WG . . . . . . . . . . . . . . . . . . . . . . . .  10
     A.2.  PCE WG  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     A.3.  SRv6OPS . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Segment routing (SR) [RFC8402] is a source routing paradigm that
   explicitly indicates the forwarding path for packets at the ingress
   node.  The ingress node steers packets into a specific path according
   to the Segment Routing Policy (SR Policy) as defined in [RFC9256].
   In order to distribute SR policies to the headend, [RFC9830]
   specifies a mechanism by using BGP.

   However, there is no identifier for segment lists in BGP SR Policy,
   which may cause inconvenience for other mechanisms to designate
   segment lists distributed by BGP.

   Consider a scenario where a network controller distributes SR
   policies to the headend nodes, which need to collect traffic
   forwarding statistics per segment list.  When a headend node reports
   each statistic to the controller, it needs to specify the segment
   list to which the statistic belongs.  Due to the lack of an



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   identifier, the headend node usually reports all SIDs in the
   associated segment list along with the statistic, and then the
   controller needs to compare the SIDs one by one to recognize which
   segment list it is.  The advertisement of all SIDs in the segment
   list consumes a lot of octets, and the comparison of SIDs can be
   complicated.

   Consider a second example where a network controller distributes SR
   policies using BGP, and then uses NETCONF to set some configurations
   of the segment lists that are not suitable to be carried in BGP.  The
   controller needs to specify which segment list these configurations
   belong to when it issues them.  In this case, a simple identifier of
   the segment list can also be helpful.

   An identifier of a segment list may also serve as a user-friendly
   attribute for debugging and troubleshooting purposes, such as
   displaying an invalid segment list when its associated BFD session is
   down.

   Section 5.7.4 of [RFC9857] defines an SR Segment List Identifier sub-
   TLV for reporting the identifier associated with a specific SID list.
   This document defines extensions to BGP SR Policy to specify the
   identifier of an SR Segment List.

1.1.  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.

2.  Segment List Identifier in SR Policy

   As defined in [RFC9830], the SR policy encoding structure is as
   follows:















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   SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
   Attributes:
      Tunnel Encapsulation Attribute (23)
         Tunnel Type: SR Policy (15)
             Binding SID
             SRv6 Binding SID
             Preference
             Priority
             Policy Name
             Policy Candidate Path Name
             Explicit NULL Label Policy (ENLP)
             Segment List
                 Weight
                 Segment
                 Segment
                 ...
             ...

                        Figure 1: SR Policy Encoding

   SR policy with segment list identifier is expressed as below:

   SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
   Attributes:
      Tunnel Encapsulation Attribute (23)
         Tunnel Type: SR Policy (15)
             Binding SID
             SRv6 Binding SID
             Preference
             Priority
             Policy Name
             Policy Candidate Path Name
             Explicit NULL Label Policy (ENLP)
             Segment List
                 Weight
                 Segment List Identifier
                 Segment
                 Segment
                 ...
             ...

         Figure 2: SR policy with segment list identifier Encoding

   The segment list identifier can be advertised using the Segment List
   ID sub-TLV, as defined in Section 2.1.






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2.1.  Segment List ID Sub-TLV

   The Segment List ID sub-TLV is defined in the BGP Tunnel
   Encapsulation Attribute [RFC9012].  The Segment List ID sub-TLV can
   be carried in the BGP Tunnel Encapsulation Attribute with the tunnel
   type set to SR Policy.

   The Segment List ID sub-TLV specifies the identifier of the segment
   list by a 4-octet number.  The Segment List ID is unique within the
   context of a Candidate Path.

   The Segment List ID sub-TLV is optional and it MUST NOT appear more
   than once inside the Segment List sub-TLV.  If multiple instances are
   present, then the first one is considered valid and the other
   instances MUST be ignored and MUST NOT considered to be malformed.

   The Segment List ID sub-TLV has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Length      |     Flags     |   RESERVED    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Segment List ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 3: Segment List ID sub-TLV

   where:

   *  Type: 19.

   *  Length: 6.

   *  Flags: 1 octet of flags.  None are defined at this stage.  Flags
      SHOULD be set to zero on transmission and MUST be ignored on
      receipt.

   *  RESERVED: 1 octet of reserved bits.  SHOULD be set to zero on
      transmission and MUST be ignored on receipt.

   *  Segment List ID: 4 octets which carry a 32-bit unsigned non-zero
      number that serves as the identifier associated with the segment
      list.  A value of 0 indicates that there is no identifier
      associated with the Segment List.  The scope of this identifier is
      the SR Policy Candidate path.





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   The validation of an SR Policy NLRI with the Segment List ID sub-TLV
   in the BGP tunnel encapsulation attribute [RFC9012] follows the
   procedures in Section 4.2 of [RFC9830].

   The Segment List ID sub-TLV is considered malformed if its format
   does not match the above description.  If its format is considered
   malformed, the associated BGP SR Policy NLRI is considered malformed
   and the "treat-as-withdraw" strategy of [RFC7606] MUST be applied.

3.  Security Considerations

   The protocol extensions defined in this document do not affect the
   base BGP security model.  The security requirements and mechanisms
   described in [RFC9830] also apply to this document.  SR operates
   within a trusted SR domain [RFC8402] and its security considerations
   also apply to BGP sessions when carrying SR Policy information.

   The Segment List ID sub-TLV is an optional sub-TLV that specifies an
   identifier associated with a segment list.  The scope of this
   identifier is the SR Policy Candidate Path.  The Segment List ID
   uniquely identifies a segment list within an SR Policy Candidate
   Path.

   The Segment List ID is assigned by a controller, distributed via BGP,
   and used as an identifier for the segment list.  Since this
   identifier may expose mission-critical or commercially sensitive
   network information, it introduces a confidentiality risk.

   Network operators MUST ensure that only trusted nodes (including both
   routers and controller applications) within the SR domain are
   permitted to receive this information.

4.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].]















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   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".

4.1.  New H3C Technologies

   *  Organization: New H3C Technologies.

   *  Implementation: H3C CR16000, CR19000 series routers
      implementation.

   *  Description: All sections including all the "MUST" and "SHOULD"
      clauses have been implemented in above-mentioned New H3C
      Products(running Version 7.1.099 and above).

   *  Maturity Level: Product

   *  Coverage: All sections.

   *  Version: Draft-03

   *  Licensing: N/A

   *  Implementation experience: Nothing specific.

   *  Contact: linchangwang.04414@h3c.com

   *  Last updated: February 10, 2025







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4.2.  ZTE Corp

   *  Organization: ZTE Corporation

   *  Implementation: ZTE's ZXR10 core router

   *  Description: The implementation in lab has been completed.  The
      commercial implementation is under development.

   *  Maturity Level: Product

   *  Coverage: All

   *  Version: Draft-03

   *  Licensing: N/A

   *  Implementation experience: Nothing specific.

   *  Contact: feng.jun99@zte.com.cn

   *  Last updated: February 6, 2025

5.  IANA Considerations

   This document defines a new Sub-TLV in the registry "SR Policy
   Segment List Sub-TLVs" [RFC9830]:

   Value     Description                   Reference
   -------------------------------------------------------
   19        Segment List ID sub-TLV       This document

6.  Acknowledgments

   The authors would like to thank Susan Hares, Hao Li, Haiyang Zhang,
   Yisong Liu, Ran Chen, Libin Liu, Lancheng Qin and Xinxin Yi for their
   review and discussion of this document.

7.  References

7.1.  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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   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [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>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

   [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>.

   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, December 2023,
              <https://www.rfc-editor.org/info/rfc9552>.

   [RFC9830]  Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
              P., and D. Jain, "Advertising Segment Routing Policies in
              BGP", RFC 9830, DOI 10.17487/RFC9830, September 2025,
              <https://www.rfc-editor.org/info/rfc9830>.

7.2.  Informative References

   [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>.

   [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>.





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   [I-D.ietf-pce-multipath]
              Koldychev, M. and S. Sidor, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Signaling
              Multipath Information", Work in Progress, Internet-Draft,
              draft-ietf-pce-multipath-24, 21 April 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
              multipath-24>.

Appendix A.  Cross WG Information

   This section describes cross-working group information for the IETF
   review process.  This section will be removed by the RFC Editor
   before publication.  The RFC Editor will also remove the references
   to [I-D.ietf-pce-multipath] and [RFC9552].

A.1.  Spring WG

   RFC9526 does not define any identifier for a Segment List.  The
   Segment List ID was introduced in all these protocols as a result of
   protocol encoding and other operational requirements.

   Consider a scenario where a network controller distributes SR
   policies to the headend nodes, which need to collect traffic
   forwarding statistics per segment list.  When a headend node reports
   each statistic to the controller, it needs to specify the segment
   list to which the statistic belongs.  Due to the lack of an
   identifier, the headend node usually reports all SIDs in the
   associated segment list along with the statistic, and then the
   controller needs to compare the SIDs one by one to recognize which
   segment list it is.  The advertisement of all SIDs in the segment
   list consumes a lot of octets, and the comparison of SIDs can be
   complicated.

   Consider a second example where a network controller distributes SR
   policies using BGP, and then uses NETCONF to set some configurations
   of the segment lists that are not suitable to be carried in BGP.  The
   controller needs to specify which segment list these configurations
   belong to when it issues them.  In this case, a simple identifier of
   the segment list can also be helpful.

   An identifier of a segment list may also serve as a user-friendly
   attribute for debugging and troubleshooting purposes, such as
   displaying an invalid segment list when its associated BFD session is
   down.

   Section 5.7.4 of [RFC9857] defines an SR Segment List Identifier sub-
   TLV for reporting the identifier associated with a specific SID list.
   Section 4.2 of [I-D.ietf-pce-multipath] defines a Path ID for SR



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   Segment Lists.  Note that the names are different due to the objects/
   TLVs in respective protocols but the semantics are identical.  This
   document defines extensions to BGP SR Policy to specify the
   identifier of an SR Segment List.

A.2.  PCE WG

   The BGP extension in this document for the identifier of segment list
   also could be implemented via PCEP according to Section 4.2 of
   [I-D.ietf-pce-multipath].  The Path ID uniquely identifies a Path
   within the context of an LSP.  Path IDs MUST be unique across all
   these path types within the same LSP.  In this document, Path IDs
   correspond to the identifier of a segment list under CP.

   Sections 4.3 and 4.4 of [I-D.ietf-pce-multipath] describe the usage
   of Path IDs in load-balancing and multiple paths for protection
   scenarios, respectively.  Additionally, Appendix A of
   [I-D.ietf-pce-multipath] specifies how Path IDs are encapsulated
   within the PCEP protocol.

A.3.  SRv6OPS

   This document is unrelated to SRv6OPS and only relates to BGP-TE
   extensions.

   [RFC9857] defines an optional sub-TLV (called SR Segment List
   Identifier sub-TLV) used to report an identifier associated with the
   specific SID list via BGP-LS.  This sub-TLV is carried in the
   optional non-transitive BGP-LS Attribute defined in [RFC9552] and are
   associated with the SR Policy Candidate Path NLRI type.

Authors' Addresses

   Changwang Lin
   New H3C Technologies
   8 Yongjia North Road
   Beijing
   Haidian District, 100094
   China
   Email: linchangwang.04414@h3c.com


   Weiqiang Cheng
   China Mobile
   32 Xuanwumen West Street
   Beijing
   Xicheng District, 100053
   China



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   Email: chengweiqiang@chinamobile.com


   Yao Liu
   ZTE
   China
   Email: liu.yao71@zte.com.cn


   Ketan Talaulikar
   Cisco Systems
   India
   Email: ketant.ietf@gmail.com


   Mengxiao Chen
   New H3C Technologies
   China
   Email: chen.mengxiao@h3c.com
































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