Segment Routing BGP Egress Peer Engineering over Layer 2 Bundle Members
draft-ietf-idr-bgp-ls-sr-epe-over-l2bundle-03

IDR Working Group                                                 C. Lin
Internet-Draft                                      New H3C Technologies
Updates: 9085, 9086 (if approved)                                  Z. Li
Intended status: Standards Track                            China Mobile
Expires: 4 December 2026                                         R. Pang
                                                            China Unicom
                                                           K. Talaulikar
                                                           Cisco Systems
                                                                 R. Chen
                                                         ZTE Corporation
                                                             2 June 2026

Segment Routing BGP Egress Peer Engineering over Layer 2 Bundle Members
             draft-ietf-idr-bgp-ls-sr-epe-over-l2bundle-03

Abstract

   There are deployments where the Layer 3 interface on which a BGP peer
   session is established is a Layer 2 interface bundle.  In order to
   allow BGP-EPE to control traffic flows on individual member links of
   the underlying Layer 2 bundle, BGP Peering SIDs need to be allocated
   to individual bundle member links, and advertisement of such BGP
   Peering SIDs in BGP-LS is required.  This document describes how to
   support Segment Routing BGP Egress Peer Engineering over Layer 2
   bundle members.  This document updates RFC9085 to allow the L2 Bundle
   Member Attributes TLV to be added to the BGP-LS Attribute associated
   with the Link NLRI of BGP peering link.  This document updates
   RFC9085 and RFC9086 to allow the PeerAdj SID TLV to be included as a
   sub-TLV of the L2 Bundle Member Attributes TLV.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 4 December 2026.

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Copyright Notice

   Copyright (c) 2026 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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Advertising Peer Adjacency Segment for L2 Bundle Member in
           BGP-LS  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  SRv6  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Manageability Considerations  . . . . . . . . . . . . . . . .   7
   5.  MC-LAG Bundles Considerations . . . . . . . . . . . . . . . .   7
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   7
     6.1.  New H3C Technologies  . . . . . . . . . . . . . . . . . .   8
     6.2.  ZTE Corp  . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Example  . . . . . . . . . . . . . . . . . . . . . .  11
   Appendix B.  Cross WG Information . . . . . . . . . . . . . . . .  13
     B.1.  Spring WG . . . . . . . . . . . . . . . . . . . . . . . .  13
     B.2.  PCE . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     B.3.  SRV6 OPS  . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Segment Routing (SR) leverages the source routing paradigm.  A node
   steers a packet through an ordered list of instructions called
   "segments".  Segment Routing can be instantiated on both MPLS and
   IPv6 data planes, which are referred to as SR-MPLS and SRv6.

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   BGP Egress Peer Engineering (BGP-EPE) allows an ingress Provider Edge
   (PE) router within the domain to use a specific egress PE and a
   specific external interface/neighbor to reach a particular
   destination.

   The SR architecture [RFC8402] defines three types of BGP Peering
   Segments that may be instantiated at a BGP node:

   *  Peer Node Segment (PeerNode SID): instruction to steer to a
      specific peer node

   *  Peer Adjacency Segment (PeerAdj SID): instruction to steer over a
      specific local interface towards a specific peer node

   *  Peer Set Segment (PeerSet SID): instruction to load-balance to a
      set of specific peer nodes

   [RFC9087] illustrates a centralized controller-based BGP-EPE solution
   involving SR path computation using the BGP Peering Segments.  A
   centralized controller learns the BGP Peering SIDs via Border Gateway
   Protocol - Link State (BGP-LS) and then uses this information to
   program a BGP-EPE policy.  [RFC9086] defines the extension to BGP-LS
   for advertisement of BGP Peering Segments along with their BGP
   peering node information.

   There are deployments where the Layer 3 interface on which a BGP peer
   session is established is a Layer 2 interface bundle (L2 Bundle), for
   instance, a Link Aggregation Group (LAG) [IEEE802.1AX].  BGP-EPE may
   wish to control traffic flows on individual member links of the
   underlying Layer 2 bundle.  In order to do so, BGP Peering SIDs need
   to be allocated to individual bundle member links, and advertisement
   of such BGP Peering SIDs in BGP-LS is required.

   This document describes how to support Segment Routing BGP Egress
   Peer Engineering over Layer 2 bundle members.

   This document updates [RFC9085] to allow the L2 Bundle Member
   Attributes TLV to be added to the BGP-LS Attribute associated with
   the Link NLRI of BGP peering link.  This document updates [RFC9085]
   and [RFC9086] to allow the PeerAdj SID TLV to be included as a sub-
   TLV of the L2 Bundle Member Attributes TLV.

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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.  Problem Statement

   In the network depicted in Figure 1, B and C establish BGP peer
   session on a Layer 2 bundle.  Assume that, the member link 1 has the
   largest available bandwidth.  The operator of AS1 wishes to apply a
   BGP-EPE policy to steer certain flows from AS1 to AS2 via member link
   1 of the Layer 2 bundle to ensure there is no over-subscription.

                    L2 Bundle      +--------+
                 /---member 1---\  |        |
               --+---member 2---+--C   AS2  |
   +--------+ /  \---member 3---/  |        |
   |        |/                     +--------+
   A   AS1  B
   |        |\                     +--------+
   +--------+ \                    |        |
               --------------------D   AS3  |
                                   |        |
                                   +--------+

                      Figure 1: BGP-EPE over L2 Bundle

   The existing Peer Adjacency SID can be allocated to the Layer 3
   interface between B and C, which is a Layer 2 interface bundle.  If
   steered by that Peer Adjacency SID, the traffic will be forwarded by
   load balancing among all the bundle member links.  So, the existing
   mechanism cannot meet the requirement of steering traffic flows via
   individual member link.

   In order to support BGP Egress Peer Engineering over Layer 2 bundle
   members, a BGP router needs to have the ability to assign Peer
   Adjacency Segments for member links.  And, the Peer Adjacency
   Segments of bundle members need to be advertised in BGP-LS, which
   will be specified in this document.

3.  Advertising Peer Adjacency Segment for L2 Bundle Member in BGP-LS

   BGP peering segments are generally advertised in BGP-LS from a BGP
   node along with its peering topology information, in order to enable
   computation of BGP-EPE policies.

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   When a BGP peer session is established over a Layer 2 interface
   bundle, an implementation MAY allocate one or more Peer Adjacency
   Segments for each member link.  If so, it SHOULD advertise the Peer
   Adjacency Segments of bundle members in BGP-LS, using the method
   defined in this section.

   In order to advertise the EPE Peer Adjacency SIDs for L2 bundle
   members in BGP-LS, the L2 Bundle Member Attributes TLVs [RFC9085]
   MUST also be included in the Link Attributes for the BGP-LS Link NLRI
   corresponding to the BGP peering session.

   Section 2.2 of [RFC9085] restricted that the L2 Bundle Member
   Attributes TLV "should only be added to the BGP-LS Attribute
   associated with the Link NLRI that describes the link of the IGP
   node".  This document updates [RFC9085] to allow the L2 Bundle Member
   Attributes TLV to be added to the BGP-LS Attribute associated with
   the Link NLRI of BGP peering link.

   Each L2 Bundle Member Attributes TLV identifies an L2 bundle member,
   and includes the EPE Peer Adjacency SID for the associated L2 bundle
   member.

   Note that the inclusion of a L2 Bundle Member Attributes TLV implies
   that the identified link is a member of the L2 bundle and that the
   member link is operationally up.  If any member link fails, an
   implementation MUST withdraw the L2 Bundle Member Attributes TLV in
   BGP-LS, along with the Peer Adjacency Segments for the failed member
   link.

3.1.  SR-MPLS

   For SR-MPLS, Section 5 of [RFC9086] defined the PeerAdj SID TLV and
   its usage for the BGP-LS advertisement of the BGP-EPE PeerAdj SID for
   L3 link.  When advertising the SR-MPLS BGP-EPE Peer Adjacency SIDs
   for L2 bundle members, the PeerAdj SID TLV [RFC9086] MUST be carried
   in the L2 Bundle Member Attributes TLV to advertise the SR-MPLS Peer
   Adjacency SID for the associated L2 bundle member.  This document
   updates [RFC9085] and [RFC9086] to allow the PeerAdj SID TLV to be
   included as a sub-TLV of the L2 Bundle Member Attributes TLV.

   When advertising SR-MPLS BGP-EPE Peer Adjacency SIDs for L2 bundle
   members, since L2 bundle information is considered a Layer 3 link
   attribute, it must be advertised in the BGP-LS Link NLRI.  The
   details for LINK NLRI are the same as those for the PeerAdj SID, as
   described in Section 5.2 of [RFC9086].  This information must not be
   included in the BGP-LS Link NLRI that corresponds to the PeerNode
   SID, as defined in Section 5.1 of [RFC9086].

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   Note that for directly connected EBGP neighbors, if a BGP neighbor is
   established over an L2 Bundle, an additional BGP-LS Link NLRI (as
   described in Section 5.2 of [RFC9086]) must be generated to advertise
   Peer Link information when generating the BGP-LS Link NLRI (as
   described in Section 5.1 of [RFC9086]) corresponding to the PeerNode
   SID.  The L2 Bundle Member Attributes TLV should be included under
   the BGP-LS Link Attribute TLVs.

   The SR-MPLS BGP-EPE Peer Adjacency SIDs for L2 bundle members are
   advertised with a BGP-LS Link NLRI, where:

   *  BGP-LS Link NLRI: as described in Section 5.2 of [RFC9086].

   *  Link Attribute TLVs:

      -  (Optional) include the PeerAdj SID TLV [RFC9086] for the
         underlying Bundle link to the BGP peer node.

      -  include the L2 Bundle Member Attributes TLV.

         o  include the PeerAdj SID TLV [RFC9086] for each L2 Bundle
            Member.

3.2.  SRv6

   For SRv6, according to Section 4.1 of [RFC9514], the SRv6 End.X SID
   TLV is used for the advertisement of L3 link BGP EPE Peer Adjacency
   SID.  When advertising the SRv6 BGP-EPE Peer Adjacency SIDs for L2
   bundle members, the SRv6 End.X SID TLV [RFC9514] MUST be carried in
   the L2 Bundle Member Attributes TLV to advertise the SRv6 Peer
   Adjacency SID for the associated L2 bundle member.

   Note Appendix A of [RFC9514], SRv6 BGP PeerNode is no longer
   advertised as BGP LINK NLRI.  When advertising SRv6 BGP-EPE Peer
   Adjacency SIDs for L2 bundle members, since L2 bundle information is
   considered a Layer 3 link attribute, it must be advertised in the
   BGP-LS Link NLRI.  The details for LINK NLRI are the same as those
   for the Peer Adjacency SID, as described in Section 5.2 of [RFC9086].

   The SRv6 BGP-EPE Peer Adjacency SIDs for L2 bundle members are
   advertised with a BGP-LS Link NLRI, where:

   *  BGP-LS Link NLRI: as described in Section 5.2 of [RFC9086].

   *  Link Attribute TLV:

      -  (Optional) include the SRv6 End.X SID TLV [RFC9514] for the
         underlying link to the BGP peer node.

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      -  include the L2 Bundle Member Attributes TLV.

         o  include the SRv6 End.X SID TLV [RFC9514] for each L2 Bundle
            Member.

4.  Manageability Considerations

   The manageability considerations described in [RFC9552] and [RFC9086]
   also apply to this document.

   The operator MUST be provided with the options of configuring,
   enabling, and disabling the advertisement of Peer Adjacency Segment
   for L2 Bundle member links, as well as control of which information
   is advertised to which internal or external peer.

5.  MC-LAG Bundles Considerations

   In environments where MC-LAG (Multi-Chassis Link Aggregation Group)
   bundles are deployed across multiple devices, it is critical to
   implement mechanisms to prevent Broadcast, Unknown Unicast, and
   Multicast (BUM) traffic from looping and ensure a loop-free network.
   The following loop prevention mechanisms are included:

   *  Split Horizon Forwarding: Each MC-LAG device maintains a split
      horizon rule where it does not forward BUM traffic received from
      one MC-LAG member port to another MC-LAG member port.  This
      prevents BUM frames from being forwarded back into the MC-LAG,
      creating loops.

   *  Designated Forwarder Election: In a typical MC-LAG configuration,
      one device is elected as the designated forwarder for BUM traffic.
      This ensures that only one device is responsible for forwarding
      BUM frames, preventing the possibility of multiple devices
      forwarding the same frame simultaneously and causing a loop.

   *  Consistent Hashing Algorithms: MC-LAG devices employ consistent
      hashing algorithms to ensure that traffic distribution across
      member links is stable and predictable.  This minimizes the risk
      of reordering and helps in effective loop prevention.

   By incorporating these mechanisms, MC-LAG deployments can effectively
   prevent BUM traffic from looping and ensure a stable, loop-free
   network.

6.  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".

6.1.  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 7.1.110 and above).

   *  Maturity Level: Product

   *  Coverage: All sections.

   *  Version: Draft-00

   *  Licensing: N/A

   *  Implementation experience: Nothing specific.

   *  Contact: li_meng_limeng@h3c.com

   *  Last updated: July 19, 2025

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6.2.  ZTE Corp

   *  Organization: ZTE Corporation

   *  Implementation: ZTE's M6000 Series Routers

   *  Description: This feature has been implemented in ZTE M6000 series
      routers and follows the definition and mechanism as defined in
      Section 3 including all the "MUST" and "SHOULD" clauses.

   *  Maturity Level: Beta

   *  Coverage: All

   *  Version: Draft-00

   *  Licensing: N/A

   *  Implementation experience: Nothing specific.

   *  Contact: zhu.xiaolong@zte.com.cn

   *  Last updated: July 19, 2025

7.  Security Considerations

   The security considerations described in [RFC9552] and [RFC9086] also
   apply to this document.

   The distribution of Layer 2 bundle information via BGP-LS exposes
   critical network adjacency details that could compromise
   infrastructure security if accessed by unauthorized parties.  This
   includes sensitive data about interface bindings, LAGs, and peer
   connectivity states.

   To mitigate risks, implementations MUST: (1) enforce strict access
   controls through BGP peer authentication [RFC5925] and route
   filtering; (2) protect data integrity using encryption for BGP-LS
   sessions in untrusted domains; and (3) implement operational
   safeguards including network segmentation and activity monitoring.
   Special consideration applies to multi-domain environments where L2
   topology exposure could reveal cross-provider interconnection
   architectures.

   Operators should monitor for emerging threats targeting exposed L2
   infrastructure data.  Regular audits of BGP-LS access patterns are
   RECOMMENDED to detect potential reconnaissance activities.

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8.  IANA Considerations

   This document has no IANA actions.

9.  Acknowledgements

   The authors would like to acknowledge Sasha Vainshtein, Acee Lindem,
   Liyan Gong, Yongqing Zhu, Lan cheng, Wisdom Tan, Yisong Liu, Libin
   Liu, Liu Yao, Hongwei Li, Allan Michael, Huo Pengfei, Gyan Mishra,
   Dong Jie, Meng Liu, Wei Wang, Yimi Zhang, Haiyang Zhang, Jiangbo
   Wang, Wisdomtan, Zheng Zhang, Yujia Gao, Alex Lee, David Wright,
   Xiaolan Wang, shawnzhsh, RuanZheng for their careful reviews and very
   helpful comments.

   The authors would also like to thank Susan Hares for her shepherd
   review and helpful comments to improve this document.

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>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [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>.

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   [RFC9085]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
              H., and M. Chen, "Border Gateway Protocol - Link State
              (BGP-LS) Extensions for Segment Routing", RFC 9085,
              DOI 10.17487/RFC9085, August 2021,
              <https://www.rfc-editor.org/info/rfc9085>.

   [RFC9086]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
              Ray, S., and J. Dong, "Border Gateway Protocol - Link
              State (BGP-LS) Extensions for Segment Routing BGP Egress
              Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
              2021, <https://www.rfc-editor.org/info/rfc9086>.

   [RFC9514]  Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
              Bernier, D., and B. Decraene, "Border Gateway Protocol -
              Link State (BGP-LS) Extensions for Segment Routing over
              IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
              2023, <https://www.rfc-editor.org/info/rfc9514>.

   [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>.

10.2.  Informative References

   [IEEE802.1AX]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Link Aggregation", IEEE 802.1AX, n.d.,
              <https://ieeexplore.ieee.org/document/7055197>.

   [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>.

   [RFC9087]  Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
              and D. Afanasiev, "Segment Routing Centralized BGP Egress
              Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
              2021, <https://www.rfc-editor.org/info/rfc9087>.

Appendix A.  Example

   This section shows an example of how Node B in Figure 1 allocates and
   advertises Peer Adjacency Segments for L2 bundle members.

   B allocates a PeerAdj SID for the Layer 2 interface bundle to peer C,
   along with a PeerAdj SID for each member link.  B programs its
   forwarding table accordingly:

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   +===============================+====================+
   |          PeerAdj SID          | Outgoing Interface |
   +---------------+---------------+                    |
   | IF on SR-MPLS |  IF on SRv6   |                    |
   |   Data Plane  |  Data Plane   |                    |
   +===============+===============+====================+
   |     1010      |     A::A0     | L2 Bundle to C     |
   +---------------+---------------+--------------------+
   |     1011      |     A::A1     | Member link 1 to C |
   +---------------+---------------+--------------------+
   |     1012      |     A::A2     | Member link 2 to C |
   +---------------+---------------+--------------------+
   |     1013      |     A::A3     | Member link 3 to C |
   +---------------+---------------+--------------------+

   B signals the related BGP-LS Link NLRI and Link Attributes including
   the PeerAdj SID for L3 parent link to the BGP-EPE controller, as
   specified in Section 5.2 of [RFC9086].  In addition, B also
   advertises L2 Bundle Member Attribute TLVs carrying the PeerAdj SIDs
   for L2 bundle members.

   For SR-MPLS, the Link Attributes are as follows:

   *  PeerAdj SID TLV (Label-1010)

   *  L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 1)

      -  PeerAdj SID TLV (Label-1011)

   *  L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 2)

      -  PeerAdj SID TLV (Label-1012)

   *  L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 3)

      -  PeerAdj SID TLV (Label-1013)

   For SRv6, the Link Attributes are as follows:

   *  SRv6 End.X SID TLV (SID-A::A0)

   *  L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 1)

      -  SRv6 End.X SID TLV (SID-A::A1)

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   *  L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 2)

      -  SRv6 End.X SID TLV (SID-A::A2)

   *  L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 3)

      -  SRv6 End.X SID TLV (SID-A::A3)

Appendix B.  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.

B.1.  Spring WG

   [RFC9087] illustrates a centralized controller-based BGP Egress Peer
   Engineering solution involving SR path computation using the BGP
   Peering Segments.  Section 4.2 of [RFC8986] explains how to use the
   End.X SID corresponding to an L2 member link.

   Section 2.2 of [RFC9085] restricted that the L2 Bundle Member
   Attributes TLV "should only be added to the BGP-LS Attribute
   associated with the Link NLRI that describes the link of the IGP
   node".  [RFC9086] defines the extension to BGP-LS for advertisement
   of BGP Peering Segments along with their BGP peering node
   information.

   This document updates [RFC9085] to allow the L2 Bundle Member
   Attributes TLV to be added to the BGP-LS Attribute associated with
   the Link NLRI of BGP peering link.  This document updates [RFC9085]
   and [RFC9086] to allow the PeerAdj SID TLV to be included as a sub-
   TLV of the L2 Bundle Member Attributes TLV.

B.2.  PCE

   This document only covers BGP-LS and does not involve PCE.

B.3.  SRV6 OPS

   Not related to SRv6 OPS, this document only addresses updates to BGP,
   and RFC9087 and RFC8986 are available for reference in SPRING.

Authors' Addresses

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

   Zhenqiang Li
   China Mobile
   China
   Email: lizhenqiang@chinamobile.com

   Ran Pang
   China Unicom
   China
   Email: pangran@chinaunicom.cn

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

   Ran Chen
   ZTE Corporation
   China
   Email: chen.ran@zte.com.cn

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