Advertising SID Algorithm Information in BGP
draft-ietf-idr-sr-te-policy-attr-04

IDR                                                               Y. Liu
Internet-Draft                                                   S. Peng
Intended status: Experimental                                        ZTE
Expires: 14 May 2026                                           G. Mishra
                                                            Verizon Inc.
                                                        10 November 2025

              Advertising SID Algorithm Information in BGP
                  draft-ietf-idr-sr-te-policy-attr-04

Abstract

   This document defines new Segment Types and proposes extensions for
   BGP to provide algorithm information for SR-MPLS Adjacency-SIDs when
   delivering SR Policy via BGP.

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 14 May 2026.

Copyright Notice

   Copyright (c) 2025 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
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  New Segment Types for SR-MPLS Adjacency with optional SR
           Algorithm . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Type L: IPv4 Node Address and Local Interface ID with
           optional SR Algorithm for SR-MPLS . . . . . . . . . . . .   4
     3.2.  Type M: IPv4 Addresses for link endpoints as Local, Remote
           pair with optional SR Algorithm for SR-MPLS . . . . . . .   5
     3.3.  Type N: IPv6 Node Addresses and Interface ID for link
           endpoints as Local, Remote pair, with optional SR Algorithm
           for SR-MPLS . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Type O: IPv6 Addresses for link endpoints as Local, Remote
           pair, with optional SR Algorithm for SR-MPLS  . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Segment Types . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  SR Policy Segment List Sub-TLVs . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Manageability Considerations  . . . . . . . . . . . . . . . .  10
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Segment Routing (SR) [RFC8402] allows a headend node to steer a
   packet flow along any path.  [RFC9256] details the concepts of SR
   Policy and steering into an SR Policy.  These apply equally to the
   MPLS and IPv6 data plane instantiations of Segment Routing with their
   respective representations of segments as SR-MPLS SID and SRv6 SID as
   described in [RFC8402].

   [RFC9830] specifies the way to use BGP to distribute information
   about one or more of the candidate paths of an SR Policy to the
   headend of that policy.  It defines a new BGP address family (SAFI),
   i.e., SR Policy SAFI NLRI.  BGP UPDATE message sends the NLRI that
   identifies an SR Policy Candidate Path, and the attributes that
   encode the segment lists and other details of that SR Policy
   Candidate Path.  These BGP attributes include the Tunnel
   Encapsulation Attribute [RFC9012] with the SR Policy Tunnel-Type, and
   it encodes SR Policy tunnel information (per [RFC9830]).

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   11 segment-descriptor types (from type A all the way to type K) for
   SR segments are defined [RFC9256] section 4.  [RFC9830] specifies the
   encoding for segment types A and B in BGP SR Policy SAFI.  And the
   encoding for the remaining 9 types are specified in [RFC9831].

   As specified in [RFC9256], the SR algorithm can be optionally
   specified for Segment Types C (IPv4 Node and SID), D (IPv6 Node and
   SID for SR-MPLS), I (IPv6 Node and SID for SRv6), J (IPv6 Node, index
   for remote and local pair, and SID for SRv6), and K (IPv6 Local/
   Remote addresses and SID for SRv6).  That is, currently the algorithm
   can be carried along with SR-MPLS prefix SID, SRv6 prefix SID and
   SRv6 adjacency SID when delivering SR Policy.

   [I-D.ietf-lsr-algorithm-related-adjacency-sid] comments that, besides
   the SR-MPLS prefix SID, the algorithm can be also included as part of
   an SR-MPLS Adjacency-SID advertisement in scenarios where multiple
   algorithm share the same link resource.  In this case, an SR-MPLS
   Policy advertised to the headend may also contain algorithm-specific
   Adjacency-SID.

   This document defines new Segment Types and proposes extensions for
   BGP to provide algorithm information for SR-MPLS Adjacency-SIDs when
   delivering SR Policy via BGP.

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.  New Segment Types for SR-MPLS Adjacency with optional SR Algorithm

   This section defines four new Segment types and the corresponding
   Segment Sub-TLVs of Segment List Sub-TLV to provide algorithm
   information for SR-MPLS Adjacency-SIDs.  The Segment Sub-TLVs in this
   document are only defined for the Segment list Sub-TLV used by the
   Tunnel Encapsulation Attribute with the SR Policy Tunnel-Type as per
   [RFC9830].  All other usages are outside the scope of this document.

   The processing procedures for SID with algorithm specified in
   [RFC9256] and [RFC9831] are still applicable for the new segment
   types.  Just as in [RFC9830], the segment list sub-TLVs specified in
   this document (sections 3.1, 3.2, 3.3, and 3.4) MAY repeat multiple
   times within the segment-list Sub-TLV.  BGP only checks the syntax of
   the fields, but the semantic meaning is check by the consumer.  When
   the algorithm is not specified for the SID types above which

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   optionally allow for it, the headend SHOULD use the Strict Shortest
   Path algorithm if available; otherwise, it SHOULD use the default
   Shortest Path algorithm.

3.1.  Type L: IPv4 Node Address and Local Interface ID with optional SR
      Algorithm for SR-MPLS

   This type allows for identification of an Adjacency SID or BGP Peer
   Adjacency SID (as defined in [RFC8402]) as an MPLS label for point-
   to-point links including IP unnumbered links.  The headend is
   required to resolve the specified IPv4 Local Node Address to the node
   originating it and then use the Local Interface ID to identify the
   point-to-point link whose adjacency is being referred to.  The Local
   Interface ID link descriptor follows semantics as specified in
   [RFC9552].  This type can also be used to indicate indirection into a
   layer 2 interface (i.e., without IP address) like a representation of
   an optical transport path or a layer 2 Ethernet port or circuit at
   the specified node.  The SR Algorithm (refer to Section 3.1.1 of
   [RFC8402] ) MAY also be provided.

   The encoding for Type L Segment Sub-TLV is as follows:

       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     |  SR Algorithm |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Local Interface ID (4 octets)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 IPv4 Node Address (4 octets)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                SR-MPLS SID (optional, 4 octets)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   Type: TBD1

   Length: Specifies the length of the value field (i.e., not including
   Type and Length fields) in terms of octets.  The value MUST be 14
   when the SR-MPLS SID is present else it MUST be 10.

   Flags: 1 octet of flags as defined in section 2.10 of [RFC9831].

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   SR Algorithm: 1 octet specifying SR Algorithm as described in
   Section 3.1.1 of [RFC8402]) when A-Flag as defined in [RFC9831] is
   present.  SR Algorithm is used by SRPM as described in Section 4 of
   [RFC9256]).  When A-Flag is not set, this field SHOULD be set to zero
   on transmission and MUST be ignored on receipt.

   Local Interface ID: 4 octets of interface index of local interface
   (refer TLV 258 of [RFC9552]).

   IPv4 Node Address: a 4-octet IPv4 address representing a node.

   SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL
   as defined in Section 2.4.4.2.1 of [RFC9830].

3.2.  Type M: IPv4 Addresses for link endpoints as Local, Remote pair
      with optional SR Algorithm for SR-MPLS

   This type allows for identification of an Adjacency SID or BGP Peer
   Adjacency SID (as defined in [RFC8402]) as an MPLS label for links.
   The headend is required to resolve the specified Local IPv4 Address
   to the node originating it and then use the Remote IPv4 Address to
   identify the link adjacency being referred to.  The Local and Remote
   Address pair link descriptors follow semantics as specified in
   [RFC9552].  The SR Algorithm (refer to Section 3.1.1 of [RFC8402])
   MAY also be provided.

   The format of Type M Segment Sub-TLV is as follows:

       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     |  SR Algorithm |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Local IPv4 Address (4 octets)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Remote IPv4 Address  (4 octets)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                SR-MPLS SID (optional, 4 octets)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   Type: TBD2

   Length: Specifies the length of the value field (i.e., not including
   Type and Length fields) in terms of octets.  The value MUST be 14
   when the SR-MPLS SID is present else it MUST be 10.

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   Flags: 1 octet of flags as defined in section 2.10 of [RFC9831].

   SR Algorithm: 1 octet specifying SR Algorithm as described in
   Section 3.1.1 of [RFC8402]) when A-Flag as defined in [RFC9831] is
   present.  SR Algorithm is used by SRPM as described in Section 4 of
   [RFC9256]).  When A-Flag is not set, this field SHOULD be set to zero
   on transmission and MUST be ignored on receipt.

   Local IPv4 Address: a 4-octet IPv4 address representing the local
   link address of the node.

   Remote IPv4 Address: a 4-octet IPv4 address representing the link
   address of the neighbor node.

   SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL
   as defined in Section 2.4.4.2.1 of [RFC9830].

3.3.  Type N: IPv6 Node Addresses and Interface ID for link endpoints as
      Local, Remote pair, with optional SR Algorithm for SR-MPLS

   This type allows for identification of an Adjacency SID or BGP Peer
   Adjacency SID (as defined in [RFC8402]) as an MPLS label for links
   including those with only Link-Local IPv6 addresses.  The headend is
   required to resolve the specified IPv6 Node Address to the node
   originating it and then use the Local Interface ID to identify the
   point-to-point link whose adjacency is being referred to.  For other
   than point-to-point links, additionally the specific adjacency over
   the link needs to be resolved using the IPv6 Remote Node Address and
   Interface ID.  The Local and Remote pair of Node Address and
   Interface ID link descriptor follows semantics as specified in
   [RFC9552].  This type can also be used to indicate indirection into a
   layer 2 interface (i.e., without IP address) like a representation of
   an optical transport path or a layer 2 Ethernet port or circuit at
   the specified node.  The SR Algorithm (refer to Section 3.1.1 of
   [RFC8402]) MAY also be provided.

   The format of Type N Segment Sub-TLV is as follows:

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       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     |  SR Algorithm |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Local Interface ID (4 octets)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                IPv6 Local Node Address (16 octets)          //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Remote Interface ID (4 octets)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                IPv6 Remote Node Address (16 octets)         //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                SR-MPLS SID (optional, 4 octets)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   Type: TBD3

   Length: Specifies the length of the value field (i.e., not including
   Type and Length fields) in terms of octets.  The value MUST be 46
   when the SR-MPLS SID is present else it MUST be 42.

   Flags: 1 octet of flags as defined in section 2.10 of [RFC9831].

   SR Algorithm: 1 octet specifying SR Algorithm as described in
   Section 3.1.1 of [RFC8402]) when A-Flag as defined in [RFC9831] is
   present.  SR Algorithm is used by SRPM as described in Section 4 of
   [RFC9256]).  When A-Flag is not set, this field SHOULD be set to zero
   on transmission and MUST be ignored on receipt.

   Local Interface ID: 4 octets of interface index of local interface
   (refer TLV 258 of [RFC9552]).

   IPv6 Local Node Address: a 16-octet IPv6 address representing the
   node.

   Remote Interface ID: 4 octets of interface index of remote interface
   (refer TLV 258 of [RFC9552]).  The value MAY be set to zero when the
   local node address and interface identifiers are sufficient to
   describe the link.

   IPv6 Remote Node Address: a 16-octet IPv6 address.  The value MAY be
   set to zero when the local node address and interface identifiers are
   sufficient to describe the link.

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   SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL
   as defined in Section 2.4.4.2.1 of [RFC9830].

3.4.  Type O: IPv6 Addresses for link endpoints as Local, Remote pair,
      with optional SR Algorithm for SR-MPLS

   This type allows for identification of an Adjacency SID or BGP Peer
   Adjacency SID (as defined in [RFC8402]) as an MPLS label for links
   with Global IPv6 addresses.  The headend is required to resolve the
   specified Local IPv6 Address to the node originating it and then use
   the Remote IPv6 Address to identify the link adjacency being referred
   to.  The Local and Remote IPv6 Address pair link descriptors follow
   semantics as specified in [RFC9552].  The SR Algorithm (refer to
   Section 3.1.1 of [RFC8402]) MAY also be provided.

   The format of Type O Segment Sub-TLV is as follows:

       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     |  SR Algorithm |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //               Local IPv6 Address (16 octets)                //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //               Remote IPv6 Address  (16 octets)              //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                SR-MPLS SID (optional, 4 octets)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   Type: TBD4

   Length: Specifies the length of the value field (i.e., not including
   Type and Length fields) in terms of octets.  The value MUST be 38
   when the SR-MPLS SID is present else it MUST be 34.

   Flags: 1 octet of flags as defined in section 2.10 of [RFC9831].

   SR Algorithm: 1 octet specifying SR Algorithm as described in
   Section 3.1.1 of [RFC8402]) when A-Flag as defined in [RFC9831] is
   present.  SR Algorithm is used by SRPM as described in Section 4 of
   [RFC9256]).  When A-Flag is not set, this field SHOULD be set to zero
   on transmission and MUST be ignored on receipt.

   Local IPv6 Address: a 16-octet IPv6 address representing the local
   link address of the node.

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   Remote IPv6 Address: a 16-octet IPv6 address representing the link
   address of the neighbor node.

   SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL
   as defined in Section 2.4.4.2.1 of [RFC9830].

4.  IANA Considerations

4.1.  Segment Types

   This document requests alphabetical identifier allocations for new
   "Segment Types" under the "Segment Routing" registry.

Value        Description                                                   Reference
-----------------------------------------------------------------------------------------
L    IPv4 Node Address and Local Interface ID
      with optional SR Algorithm for SR-MPLS                               This document
M    IPv4 Addresses for link endpoints as Local, Remote pair
      with optional SR Algorithm for SR-MPLS                               This document
N    IPv6 Node Addresses and Interface ID for link endpoints
      as Local, Remote pair, with optional SR Algorithm for SR-MPLS        This document
O    IPv6 Addresses for link endpoints as Local, Remote pair,
      with optional SR Algorithm for SR-MPLS                               This document

4.2.  SR Policy Segment List Sub-TLVs

   This document requests the following code points from the "SR Policy
   Segment List Sub-TLVs" registry [RFC9830] under the "Border Gateway
   Protocol (BGP) Tunnel Encapsulation" registry group.

Value  Description                                          Reference
------------------------------------------------------------------------
TBD1  Segment Type L sub-TLV                              This document
TBD2  Segment Type M sub-TLV                              This document
TBD3  Segment Type N sub-TLV                              This document
TBD4  Segment Type O sub-TLV                              This document

5.  Security Considerations

   This document defines new sub-TLVs of the Segment List sub-TLV used
   and only used under the Tunnel Encapsulation Attribute with the SR
   Policy Tunnel-Type[RFC9830] to carry the information of new segment
   types as introduced in this document, i.e, SR-MPLS Adjacency-SIDs
   with operational algorithm information.

   Procedures and protocol extensions defined in this document do not
   affect the security considerations discussed in [RFC9256] and
   [RFC9830].

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   The information in segment types L-O defined in this document is
   critical pieces of information about the infrastructure of a network
   or multiple network segments, more specifically, these information
   includes endpoint/node addresses, SR SIDs, and the SR algorithms.

   The operators need to carefully restrict access to the information
   contained in segments L-O, it is the responsibility of the network
   operators to ensure that only trusted nodes (that include both
   routers and controller applications) within the SR domain are
   configured to receive such information.

6.  Manageability Considerations

   The operations and manageability considerations in [RFC9830] apply to
   the segment types defined in this document.

   The YANG model for the operation and management of SR Policies
   [I-D.ietf-spring-sr-policy-yang] reports the SR Policies provisioned
   via BGP SR Policy SAFI along with their operational states.  And
   [RFC9857] enables the reporting of the operational state of the SR
   Policies from the headend to the controllers via BGP-LS.

   Currently this document is experimental and there's no implementation
   yet.  But it is RECOMMENDED to include the information of new segment
   types in both BGP-LS UPDATE and YANG model for SR Policies, so
   potential implementations in the future would benefit from it.

7.  Acknowledgement

   The authors would like to thank Ketan Talaulikar, Nat Kao and
   Zhenqiang Li for their comments and suggestions.  The authors would
   like to thank Susan Hares for her detailed shepherd review that
   helped in improving the document.

8.  References

8.1.  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>.

   [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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   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

   [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>.

   [RFC9831]  Talaulikar, K., Ed., Filsfils, C., Previdi, S., Mattes,
              P., and D. Jain, "Segment Type Extensions for BGP Segment
              Routing (SR) Policy", RFC 9831, DOI 10.17487/RFC9831,
              September 2025, <https://www.rfc-editor.org/info/rfc9831>.

8.2.  Informative References

   [I-D.ietf-lsr-algorithm-related-adjacency-sid]
              Chen, R., Peng, S., Talaulikar, K., and P. Psenak,
              "Algorithm Related IGP-Adjacency SID Advertisement", Work
              in Progress, Internet-Draft, draft-ietf-lsr-algorithm-
              related-adjacency-sid-08, 16 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
              algorithm-related-adjacency-sid-08>.

   [I-D.ietf-spring-sr-policy-yang]
              Saleh, T., Raza, S. K., Zhuang, S., Matsushima, S., and V.
              P. Beeram, "YANG Data Model for Segment Routing Policy",
              Work in Progress, Internet-Draft, draft-ietf-spring-sr-
              policy-yang-06, 20 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              sr-policy-yang-06>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

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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>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC8665]  Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
              H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", RFC 8665,
              DOI 10.17487/RFC8665, December 2019,
              <https://www.rfc-editor.org/info/rfc8665>.

   [RFC8666]  Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
              for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
              December 2019, <https://www.rfc-editor.org/info/rfc8666>.

   [RFC8667]  Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
              Extensions for Segment Routing", RFC 8667,
              DOI 10.17487/RFC8667, December 2019,
              <https://www.rfc-editor.org/info/rfc8667>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [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>.

   [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>.

Authors' Addresses

Liu, et al.                Expires 14 May 2026                 [Page 12]
Internet-Draft                BGP SID Algo                 November 2025

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

   Shaofu Peng
   ZTE
   Nanjing
   China
   Email: peng.shaofu@zte.com.cn

   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com

Liu, et al.                Expires 14 May 2026                 [Page 13]