BGP SR Policy Extensions for Administrative Flags
draft-ietf-idr-sr-policy-admin-flags-00

IDR                                                              C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                                 Y. Liu
Expires: January 20, 2027                                  China Mobile
                                                               Ran.Chen
                                                                    ZTE
                                                            A. Karboubi
                                                                  Ciena
                                                               T. Zhang
                                                                   BUPT
                                                                G. Zeng
                                                                 Huawei
                                                          July 19, 2026

             BGP SR Policy Extensions for Administrative Flags
                  draft-ietf-idr-sr-policy-admin-flags-00

Abstract

   Segment Routing 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 an extension to the BGP SR Policy that sets
   the administrative state of the candidate path or segment list,
   facilitating the operation and maintenance of the SR Policy.

Status of this Memo

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   This Internet-Draft will expire on January 20, 2027.

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Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Admin State in SR Policy.......................................3
      2.1. Candidate Path Administrative Flags Sub-TLV...............5
      2.2. Segment List Administrative Flags Sub-TLV.................6
   3. Security Considerations........................................7
   4. IANA Considerations............................................7
   5. References.....................................................8
      5.1. Normative References......................................8
      5.2. Informative References....................................9
   Appendix A. Cross WG Information.................................10
      A.1. Link to Spring WG........................................10
      A.2. Interaction with PCE WG..................................10
      A.3. Interaction with SRV6ops Recommendations.................10
   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.

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   For management purposes, the controller may occasionally need to
   temporarily divert traffic from a specific forwarding path and then
   restore it later. In such cases, the controller can issue an
   Administrative Down command to a specific path in the SR Policy on
   the device without removing the path. When it is time to restore the
   path, the controller can simply issue an Administrative Up command
   to that same path.

   In another scenario, such as in 6PE or EPE situations where it is
   necessary to conserve service route SIDs, the SR Policy Flag can be
   extended to indicate settings. For example, configuring the
   Candidate Path as "Ignore service routes Prefix SID" can help
   optimize the segment list.

   In some scenarios, the Candidate Path cannot be used as a backup
   path. The operator needs to control the Candidate Path status to
   identify whether this CP can serve as a backup path.

   In [RFC9256], section 8.2 defines the Drop-Upon-Invalid behavior. An
   SR Policy MAY be enabled for the Drop-Upon-Invalid behavior.
   Currently, there is no behavior control for Drop-Upon-Invalid on the
   path of an SR policy.

   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.  [I-D. draft-ietf-spring-srv6-policy-sid-
   list-opt] specifies procedures to indicate whether the endpoint's
   node SID needs to be included or excluded when installing the SRv6
   Policy.

   This document defines an extension to the BGP SR Policy that sets
   the management state of the candidate path or the segment list,
   facilitating the operation and maintenance of the SR Policy.

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. Admin State 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 Encaps Attribute (23)
            Tunnel Type: SR Policy
                Binding SID
                SRv6 Binding SID
                Preference
                Priority
                Policy Name
                Policy Candidate Path Name
                Explicit NULL Label Policy (ENLP)
                Segment List
                    Weight
                    Segment
                    Segment
                    ...
                ...

   SR policy with Administrative Flags are expressed as below:

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

   The Candidate Path Administrative Flags can also be advertised using
   the Candidate Path Administrative Flags sub-TLV, as defined in
   Section 2.1.

   The segment list Administrative Flags can be advertised using the
   Segment List Administrative Flags sub-TLV, as defined in Section
   2.2.

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2.1. Candidate Path Administrative Flags Sub-TLV

   The Candidate Path Administrative Flags sub-TLV is used to indicate
   the AdminState of the Candidate Path.

   The Candidate Path Administrative Flags sub-TLV is optional and it
   MUST NOT appear more than once inside the Segment List sub-TLV.

   The Candidate Path Administrative Flags 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 2
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Length      |              Flags            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o Type: TBD1.

   o Length: 2.

   o Flags: 2 octet of flags.

   0   1   2   3   4   5   6  7  8  9  0  1  2  3  4  5  6
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   | S | B | I | D | E |IFN|              Reserved                 |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
                Figure 5: Administrative Flags

      where:

        -  S-Flag: Indicates the CP is in an administrative shut state

           when set.

        -  B-Flag: Indicates the CP is configured as "backup
           ineligible".

        -  I-Flag: Indicates the CP is configured as "Ignore service
           route's Prefix SID". It allows traffic to a BGP service route
           to be steered over an SR policy without imposing the service
           route's prefix label or SRv6 Service SID.

        -  D-Flag: Indicates the CP has been marked as the "Drop Upon
           Invalid" behavior as described in section 8.2 of [RFC9256].

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        - E-Flag: Indicates that the CP is set to 'candidate path
           eligible' as defined in [I-D. ietf-spring-sr-policy-
           eligibility]. If set, it indicates that the eligibility
           attribute of the candidate path is true. If not set, it
           indicates that the eligibility attribute of the candidate
           path is false.

        - IFN-flag (Install Final Node-sid flag) as defined in [I-D.
           ietf-spring-srv6-policy-sid-list-opt]: indicate the endpoint
           node SID is included in installing SID list(s) of the
           Candidate Path (CP) when set. 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.

        - Reserved: The unassigned bits in the Flags field MUST be set
           to zero upon transmission and MUST be ignored upon receipt.

2.2. Segment List Administrative Flags Sub-TLV

   The Segment List Administrative Flags sub-TLV is used to indicate
   the AdminState of the Segment List of Candidate Path.

   The Segment List Administrative Flags sub-TLV is optional and it
   MUST NOT appear more than once inside the Segment List sub-TLV.

   The Segment List Administrative Flags 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 2
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Length      |             Flags             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o Type: TBD2.

   o Length: 2.

   o Flags: 2 octet of flags.

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   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|E|       Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 6: Administrative Flags

      where:

        -  S-Flag: Indicates the Segment List is in an administrative
           shut state when set.

        - E-Flag: When set, indicates the Segment List is in an eligible
           state (capable of forwarding traffic).
           When cleared, indicates the Segment List is ineligible
           (cannot forward traffic).

        - Reserved: The unassigned bits in the Flags field MUST be set
           to zero upon transmission and MUST be ignored upon receipt.

3. Security Considerations

   The security considerations of BGP [RFC4271] and BGP SR policy
   [RFC9830] apply to this document.

   The Candidate Path Administrative Flags sub-TLV is used to indicate
   the AdminState of the Candidate Path. The Segment List
   Administrative Flags sub-TLV is used to indicate the AdminState of
   the Segment List of the Candidate Path. The values of these two sub-
   TLVs affect the state of the Candidate Path or Segment List in the
   SR Policy, which may consequently impact packet forwarding in the
   network. Therefore, when configuring, querying, and reporting
   control plane Candidate Path Administrative Flags and Segment List
   Administrative Flags in BGP, care must be taken to protect this
   mission critical or commercially sensitive information.

4. IANA Considerations

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

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   Value    Description                         Reference
   -------------------------------------------------------
   TBD1     Candidate Path Administrative Flags sub-TLV     This
   document
   TBD2     Segment List Administrative Flags sub-TLV       This
   document

5. References

5.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
             Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI
             10.17487/RFC4271, January 2006, <https://www.rfc-
             editor.org/info/rfc4271>.

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, May 2017

   [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>.

   [RFC9830] Previdi, S., Filsfils, C., Talaulikar, K., 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>.

   [I-D. ietf-spring-sr-policy-eligibility] Karboubi, A., Shah, H.,
             Sivalaban, S., Stone, A. and Schmutz, C., "Eligibility
             Concept in Segment Routing Policies", draft-ietf-spring-
             sr-policy-eligibility-00 (work in progress), January 2026.

   [I-D. draft-ietf-spring-srv6-policy-sid-list-opt] Z. Ali, C. Lin, Y.
             Liu, R. Chen and C. Li, "SRv6 Policy SID List
             Optimization", Work in Progress, Internet-Draft, draft-
             ietf-spring-srv6-policy-sid-list-opt, 25 November
             2025,<https://datatracker.ietf.org/doc/html/draft-ietf-
             spring-srv6-policy-sid-list-opt-00>.

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   [I-D. draft-all-pce-srv6-policy-sid-list-optimization] Z. Ali, C.
             Lin, Y. Liu, R. Chen and C. Li, "Path Computation Element
             Communication Protocol (PCEP) extensions for SRv6 Policy
             SID List Optimization", Work in Progress, Internet-Draft,
             draft-all-pce-srv6-policy-sid-list-optimization, 02 March
             2026, <https://datatracker.ietf.org/doc/html/draft-all-
             pce-srv6-policy-sid-list-optimization-04>.

5.2. Informative References

   [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>.

   [I-D. draft-karboubi-spring-sidlist-optimized-cs-sr] Karboubi, A.,
             Alaettinoglu, C., Shah, H., Sivabalan, S., Defillipi, T.,
             and Maheshwari, P., "Circuit Style Segment Routing
             Policies with Optimized SID List Depth", Work in Progress,
             Internet-Draft, draft-karboubi-spring-sidlist-optimized-
             cs-sr-03, 2 June 2025,
             <https://datatracker.ietf.org/doc/html/draft-karboubi-
             spring-sidlist- -cs-sr-03>.

   [I-D. draft-ietf-srv6ops-srv6-deployment] McBride, M., Liu, Y., Li,
             Z., Durmus, M., Erdogan, E., Mishra, G., and Horn, J.,
             "SRv6 Deployment Options", Work in Progress, Internet-
             Draft, draft-ietf-srv6ops-srv6-deployment, 25 February
             2026,<https://datatracker.ietf.org/doc/html/draft-ietf-
             srv6ops-srv6-deployment-02>.

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Appendix A. Cross WG Information

   This section describes cross-working group information for use
   during the IETF review process. This section will be removed by the
   RFC editor prior to publication.

A.1. Link to Spring WG

   This document implements the features defined in Section 4 of [I-
   D.ietf-spring-sr-policy-eligibility], Section 8.2 of [RFC9256], and
   Section 3.2 of [I-D.draft-ietf-spring-srv6-policy-sid-list-opt] via
   BGP. These SPRING features require the implementation of this
   document.

A.2. Interaction with PCE WG

   The BGP extension defined by this document also may be implemented
   by a new TLV of PCEP according to Section 4.3 of [I-D. draft-
   karboub-spring-sidlist-optimized-cs-sr].

   The optimization feature implemented in BGP by this document also
   could be implemented in PCEP according to Section 3.1 of [I-D.
   draft-ietf-spring-srv6-policy-sid-list-opt].

   [I-D. draft-all-pce-srv6-policy-sid-list-optimization] specifies a
   PCEP extension to indicate whether the endpoint's node SID needs to
   be included or excluded when installing the SRv6 Policy.

A.3. Interaction with SRV6ops Recommendations

   This optimization feature could be distributed to external
   components using BGP-LS extension defined in [I-D. draft-lin-idr-
   bgp-ls-sr-policy-admin-flag].

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 Authors' Addresses

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

   Yisong Liu
   China Mobile
   32 Xuanwumen West Street
   Beijing
   Xicheng District, 100053
   China
   Email: liuyisong@chinamobile.com

   Ran Chen
   ZTE Corporation

   Email: chen.ran@zte.com.cn

   Amal Karboubi
   Ciena
   Email: akarboub@ciena.com

   Tiankui Zhang
   BUPT
   Email: zhangtiankui@bupt.edu.cn

   Guanming Zeng
   Huawei
   Email: zengguanming@huawei.com

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