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Advertising SID Algorithm Information in BGP
draft-peng-idr-segment-routing-te-policy-attr-09

Document Type Active Internet-Draft (idr WG)
Authors Yao Liu , Shaofu Peng , Gyan Mishra
Last updated 2024-03-17
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draft-peng-idr-segment-routing-te-policy-attr-09
IDR                                                               Y. Liu
Internet-Draft                                                   S. Peng
Intended status: Experimental                                        ZTE
Expires: 18 September 2024                                     G. Mishra
                                                            Verizon Inc.
                                                           17 March 2024

              Advertising SID Algorithm Information in BGP
            draft-peng-idr-segment-routing-te-policy-attr-09

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.

   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 18 September 2024.

Copyright Notice

   Copyright (c) 2024 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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   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.

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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
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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].

   [I-D.ietf-idr-sr-policy-safi] specifies the way to use BGP to
   distribute 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.  In UPDATE messages of that address
   family, the NLRI identifies an SR Policy Candidate Path, and the
   attributes encode the segment lists and other details of that SR
   Policy Candidate Path.

   11 segment-descriptor types (from type A all the way to type K) for
   SR segments are defined [RFC9256] section 4.
   [I-D.ietf-idr-sr-policy-safi] 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
   [I-D.ietf-idr-bgp-sr-segtypes-ext].

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   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] complements 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 processing procedures for SID with algorithm specified in
   [RFC9256] and [I-D.ietf-idr-bgp-sr-segtypes-ext] are still applicable
   for the new segment types.  When the algorithm is not specified for
   the SID types above which optionally allow for it, the headend SHOULD
   use the Strict Shortest Path algorithm if available; otherwise, it
   SHOULD use the default Shortest Path algorithm.

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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] ) SR-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
   [I-D.ietf-idr-bgp-sr-segtypes-ext].

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

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   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 [I-D.ietf-idr-sr-policy-safi].

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]) SR-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.

   Flags: 1 octet of flags as defined in
   [I-D.ietf-idr-bgp-sr-segtypes-ext].

   SR Algorithm: 1 octet specifying SR Algorithm as described in
   Section 3.1.1 of [RFC8402]) when A-Flag as defined in
   [I-D.ietf-idr-bgp-sr-segtypes-ext] is present.  SR Algorithm is used

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   by SRPM as described in Section 4 of [RFC9256]).  When A-Flag is not
   encoded, 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 [I-D.ietf-idr-sr-policy-safi].

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]) 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
   [I-D.ietf-idr-bgp-sr-segtypes-ext].

   SR Algorithm: 1 octet specifying SR Algorithm as described in
   Section 3.1.1 of [RFC8402]) when A-Flag as defined in
   [I-D.ietf-idr-bgp-sr-segtypes-ext] is present.  SR Algorithm is used
   by SRPM as described in Section 4 of [RFC9256]).  When A-Flag is not
   encoded, 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 [I-D.ietf-idr-sr-policy-safi].

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]) 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.

   TThe 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
   [I-D.ietf-idr-bgp-sr-segtypes-ext].

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

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

   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 [I-D.ietf-idr-sr-policy-safi].

4.  IANA Considerations

   This document requests codepoint allocations for new Sub-TLVs of the
   "Segment List sub-TLV" under the "BGP Tunnel Encapsulation".

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

   Procedures and protocol extensions defined in this document do not
   affect the security considerations discussed in [RFC9256] and
   [I-D.ietf-idr-sr-policy-safi].

6.  Acknowledgement

   The authors would like to thank Ketan Talaulikar, Nat Kao and
   Zhenqiang Li for their comments and suggestions.

7.  References

7.1.  Normative References

   [I-D.ietf-idr-bgp-sr-segtypes-ext]
              Talaulikar, K., Filsfils, C., Previdi, S., Mattes, P., and
              D. Jain, "Segment Routing Segment Types Extensions for BGP
              SR Policy", Work in Progress, Internet-Draft, draft-ietf-
              idr-bgp-sr-segtypes-ext-03, 4 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
              sr-segtypes-ext-03>.

   [I-D.ietf-idr-sr-policy-safi]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
              D. Jain, "Advertising Segment Routing Policies in BGP",
              Work in Progress, Internet-Draft, draft-ietf-idr-sr-

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              policy-safi-02, 16 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
              policy-safi-02>.

   [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>.

   [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>.

7.2.  Informative References

   [I-D.ietf-lsr-algorithm-related-adjacency-sid]
              Peng, S., Chen, R., Talaulikar, K., and P. Psenak,
              "Algorithm Related IGP-Adjacency SID Advertisement", Work
              in Progress, Internet-Draft, draft-ietf-lsr-algorithm-
              related-adjacency-sid-06, 5 December 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
              algorithm-related-adjacency-sid-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>.

   [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>.

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   [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>.

Authors' Addresses

   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

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