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rfc:rfc9514



Internet Engineering Task Force (IETF) G. Dawra Request for Comments: 9514 LinkedIn Category: Standards Track C. Filsfils ISSN: 2070-1721 K. Talaulikar, Ed.

                                                         Cisco Systems
                                                               M. Chen
                                                                Huawei
                                                            D. Bernier
                                                           Bell Canada
                                                           B. Decraene
                                                                Orange
                                                         December 2023
Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment
                      Routing over IPv6 (SRv6)

Abstract

 Segment Routing over IPv6 (SRv6) allows for a flexible definition of
 end-to-end paths within various topologies by encoding paths as
 sequences of topological or functional sub-paths called "segments".
 These segments are advertised by various protocols such as BGP, IS-
 IS, and OSPFv3.
 This document defines extensions to BGP - Link State (BGP-LS) to
 advertise SRv6 segments along with their behaviors and other
 attributes via BGP.  The BGP-LS address-family solution for SRv6
 described in this document is similar to BGP-LS for SR for the MPLS
 data plane, which is defined in RFC 9085.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc9514.

Copyright Notice

 Copyright (c) 2023 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 and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Revised BSD License text as described in Section 4.e of the
 Trust Legal Provisions and are provided without warranty as described
 in the Revised BSD License.

Table of Contents

 1.  Introduction
   1.1.  Requirements Language
 2.  BGP-LS Extensions for SRv6
 3.  SRv6 Node Attributes
   3.1.  SRv6 Capabilities TLV
   3.2.  SRv6 Node MSD Types
 4.  SRv6 Link Attributes
   4.1.  SRv6 End.X SID TLV
   4.2.  SRv6 LAN End.X SID TLV
   4.3.  SRv6 Link MSD Types
 5.  SRv6 Prefix Attributes
   5.1.  SRv6 Locator TLV
 6.  SRv6 SID NLRI
   6.1.  SRv6 SID Information TLV
 7.  SRv6 SID Attributes
   7.1.  SRv6 Endpoint Behavior TLV
   7.2.  SRv6 BGP PeerNode SID TLV
 8.  SRv6 SID Structure TLV
 9.  IANA Considerations
   9.1.  BGP-LS NLRI Types
   9.2.  BGP-LS NLRI and Attribute TLVs
   9.3.  SRv6 BGP EPE SID Flags
 10. Manageability Considerations
 11. Security Considerations
 12. References
   12.1.  Normative References
   12.2.  Informative References
 Appendix A.  Differences with BGP-EPE for SR-MPLS
 Acknowledgements
 Contributors
 Authors' Addresses

1. Introduction

 SRv6 refers to Segment Routing instantiated on the IPv6 data plane
 [RFC8402].  An SRv6 segment is often referred to by its SRv6 Segment
 Identifier (SID).
 The network programming paradigm [RFC8986] is central to SRv6.  It
 describes how different behaviors can be bound to SIDs and how a
 network program can be expressed as a combination of SIDs.
 An SRv6-capable node maintains all the SRv6 segments explicitly
 instantiated locally.
 The IS-IS and OSPFv3 link-state routing protocols have been extended
 to advertise some of these SRv6 SIDs and SRv6-related information
 [RFC9352] [RFC9513].  Other SRv6 SIDs may be instantiated on a node
 via other mechanisms for topological or service functionalities.
 The advertisement of SR-related information along with the topology
 is specified in [RFC9085] for the MPLS data plane instantiation (SR-
 MPLS) and in [RFC9086] for BGP Egress Peer Engineering (EPE).  On
 similar lines, introducing the SRv6-related information in BGP-LS
 allows consumer applications that require topological visibility to
 also receive the SRv6 SIDs from nodes across an IGP domain or even
 across Autonomous Systems (ASes) as required.  This allows
 applications to leverage the SRv6 capabilities for network
 programming.
 The identifying key of each link-state object, namely a node, link,
 or prefix, is encoded in the Network Layer Reachability Information
 (NLRI), and the properties of the object are encoded in the BGP-LS
 Attribute [RFC7752].
 This document describes extensions to BGP-LS to advertise the SRv6
 SIDs and other SRv6 information from all the SRv6-capable nodes in
 the IGP domain when sourced from link-state routing protocols and
 directly from individual SRv6-capable nodes (e.g., when sourced from
 BGP for EPE).

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. BGP-LS Extensions for SRv6

 BGP-LS [RFC7752] defines the Node, Link, and Prefix Link-State NLRI
 types and the advertisement of their attributes via BGP.
 When a BGP-LS router advertises topology information that it sources
 from the underlying link-state routing protocol, it derives the
 corresponding SRv6 information from the SRv6 extensions for IS-IS
 [RFC9352] or OSPFv3 [RFC9513] as applicable.  In practice, this
 derivation comprises a simple copy of the relevant fields from the
 IS-IS or OSPFv3 TLV/sub-TLV into the fields of the corresponding BGP-
 LS TLV/sub-TLV.  When a BGP-LS router advertises topology information
 from the BGP routing protocol (e.g., for EPE) or advertises SRv6 SIDs
 associated with a node using Direct as the Protocol-ID, it derives
 the SRv6 information from the local node.  Such information is
 advertised only on behalf of the local router, in contrast to the
 advertisement of information from all nodes of an IGP domain when
 sourced from a link-state routing protocol.
 The SRv6 information pertaining to a node is advertised via the BGP-
 LS Node NLRI using the BGP-LS Attribute TLVs as follows:
  • The SRv6 capabilities of the node are advertised via the SRv6

Capabilities TLV (Section 3.1).

  • Maximum SID Depth (MSD) types introduced for SRv6 are advertised

(Section 3.2) using the Node MSD TLV specified in [RFC8814].

  • Algorithm support for SRv6 is advertised via the SR-Algorithm TLV

specified in [RFC9085].

 The SRv6 information pertaining to a link is advertised via the BGP-
 LS Link NLRI using the BGP-LS Attribute TLVs as follows:
  • The SRv6 SID of the IGP Adjacency SID or the BGP EPE Peer

Adjacency SID [RFC8402] is advertised via the SRv6 End.X SID TLV

    introduced in this document (Section 4.1).
  • The SRv6 SID of the IGP Adjacency SID to a non-Designated Router

(DR) or non-Designated Intermediate System (DIS) [RFC8402] is

    advertised via the SRv6 LAN End.X SID TLV introduced in this
    document (Section 4.2).
  • MSD types introduced for SRv6 are advertised (Section 4.3) using

the Link MSD TLV specified in [RFC8814].

 The SRv6 information pertaining to a prefix is advertised via the
 BGP-LS Prefix NLRI using the BGP-LS Attribute TLVs as follows:
  • The SRv6 Locator is advertised via the SRv6 Locator TLV introduced

in this document (Section 5.1).

  • The attributes of the SRv6 Locator are advertised via the Prefix

Attribute Flags TLV specified in [RFC9085].

 The SRv6 SIDs associated with the node are advertised using the BGP-
 LS SRv6 SID NLRI introduced in this document (Section 6).  This
 enables the BGP-LS encoding to scale to cover a potentially large set
 of SRv6 SIDs instantiated on a node with the granularity of
 individual SIDs and without affecting the size and scalability of the
 BGP-LS updates.  If the SRv6 SIDs had been advertised within the BGP-
 LS Link Attribute associated with the existing Node NLRI, the BGP-LS
 update would have grown rather large with the increase in SRv6 SIDs
 on the node and would have also required a large update message to be
 generated for any change, even a change to a single SRv6 SID.  BGP-LS
 Attribute TLVs for the SRv6 SID NLRI are introduced in this document
 as follows:
  • The Endpoint behavior of the SRv6 SID is advertised via the SRv6

Endpoint Behavior TLV (Section 7.1).

  • The BGP EPE Peer Node context for a PeerNode SID and the Peer Set

context for a PeerSet SID [RFC8402] are advertised via the SRv6

    BGP PeerNode SID TLV (Section 7.2).
 Subsequent sections of this document specify the encoding and usage
 of these extensions.  All the TLVs introduced follow the formats and
 common field definitions provided in [RFC7752].

3. SRv6 Node Attributes

 The SRv6 attributes of a node are advertised using the BGP-LS
 Attribute TLVs defined in this section and associated with the BGP-LS
 Node NLRI.

3.1. SRv6 Capabilities TLV

 This BGP-LS Attribute TLV is used to announce the SRv6 capabilities
 of the node along with the BGP-LS Node NLRI and indicates the SRv6
 support by the node.  A single instance of this TLV MUST be included
 in the BGP-LS Attribute for each SRv6-capable node.  The IS-IS SRv6
 Capabilities sub-TLV [RFC9352] and the OSPFv3 SRv6 Capabilities TLV
 [RFC9513] that map to this BGP-LS TLV are specified with the ability
 to carry optional sub-sub-TLVs and sub-TLVs.  However, no such
 extensions are currently defined.  Moreover, the SRv6 Capabilities
 TLV defined below is not extensible.  As a result, it is expected
 that any extensions will be introduced as top-level TLVs in the BGP-
 LS Attribute.  The SRv6 Capabilities TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             Flags             |         Reserved              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 Figure 1: SRv6 Capabilities TLV Format
 where:
 Type:  1038
 Length:  4
 Flags:  2-octet field.  The flags are copied from the IS-IS SRv6
    Capabilities sub-TLV (Section 2 of [RFC9352]) or from the OSPFv3
    SRv6 Capabilities TLV (Section 2 of [RFC9513]) in the case of IS-
    IS or OSPFv3, respectively.
 Reserved:  2-octet field that MUST be set to 0 when originated and
    ignored on receipt.

3.2. SRv6 Node MSD Types

 The Node MSD TLV [RFC8814] of the BGP-LS Attribute of the Node NLRI
 is also used to advertise the limits and the Segment Routing Header
 (SRH) [RFC8754] operations supported by the SRv6-capable node.  The
 SRv6 MSD types specified in Section 4 of [RFC9352] are also used with
 the BGP-LS Node MSD TLV, as these code points are shared between the
 IS-IS, OSPF, and BGP-LS protocols.  The description and semantics of
 these new MSD types for BGP-LS are identical to those specified in
 [RFC9352].
 Each MSD type is encoded in the BGP-LS Node MSD TLV as a one-octet
 type followed by a one-octet value as derived from the IS-IS or
 OSPFv3 Node MSD advertisements specified in [RFC8814].

4. SRv6 Link Attributes

 SRv6 attributes and SIDs associated with a link or adjacency are
 advertised using the BGP-LS Attribute TLVs defined in this section
 and associated with the BGP-LS Link NLRI.

4.1. SRv6 End.X SID TLV

 The SRv6 End.X SID TLV is used to advertise the SRv6 SIDs associated
 with an IGP Adjacency SID behavior that correspond to a point-to-
 point or point-to-multipoint link or adjacency of the node running
 the IS-IS or OSPFv3 protocols.  The information advertised via this
 TLV is derived from the IS-IS SRv6 End.X SID sub-TLV (Section 8.1 of
 [RFC9352]) or the OSPFv3 SRv6 End.X SID sub-TLV (Section 9.1 of
 [RFC9513]) in the case of IS-IS or OSPFv3, respectively.  This TLV
 can also be used to advertise the SRv6 SID corresponding to the
 underlying Layer 2 member links for a Layer 3 bundle interface as a
 sub-TLV of the L2 Bundle Member Attribute TLV [RFC9085].
 This TLV is also used by BGP-LS to advertise the BGP EPE Peer
 Adjacency SID for SRv6 on the same lines as specified for SR-MPLS in
 [RFC9086].  The SRv6 SID for the BGP Peer Adjacency using End.X
 behaviors (viz. End.X, End.X with PSP, End.X with USP, and End.X with
 PSP & USP) [RFC8986] indicates the cross-connect to a specific Layer
 3 link to the specific BGP session peer (neighbor).
 More than one instance of this TLV (one for each SRv6 End.X SID) can
 be included in the BGP-LS Attribute.
 The TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Endpoint Behavior      |      Flags    |   Algorithm   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Weight    |   Reserved    |  SID (16 octets) ...          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)             | Sub-TLVs (variable) . . .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 2: SRv6 End.X SID TLV Format
 where:
 Type:  1106
 Length:  variable
 Endpoint Behavior:  2-octet field.  The Endpoint behavior code point
    for this SRv6 SID as defined in Section 10.2 of [RFC8986].
 Flags:  1 octet of flags.  The flags are copied from the IS-IS SRv6
    End.X SID sub-TLV (Section 8.1 of [RFC9352]) or the OSPFv3 SRv6
    End.X SID sub-TLV (Section 9.1 of [RFC9513]) in the case of IS-IS
    or OSPFv3, respectively.  In the case of the BGP EPE Peer
    Adjacency SID, the flags are as defined in Section 7.2.
 Algorithm:  1-octet field.  Algorithm associated with the SID.
 Weight:  1-octet field.  The value represents the weight of the SID
    for the purpose of load balancing.  The use of the weight is
    defined in [RFC8402].
 Reserved:  1-octet field that MUST be set to 0 when originated and
    ignored on receipt.
 SID:  16-octet field.  This field encodes the advertised SRv6 SID as
    a 128-bit value.
 Sub-TLVs:  Used to advertise sub-TLVs that provide additional
    attributes for the specific SRv6 SID.  This document defines one
    in Section 8.

4.2. SRv6 LAN End.X SID TLV

 For a LAN interface, an IGP node ordinarily announces only its
 adjacency to the IS-IS pseudonode (or the equivalent OSPF DR).  The
 information advertised via this TLV is derived from the IS-IS SRv6
 LAN End.X SID sub-TLV (Section 8.2 of [RFC9352]) or the OSPFv3 SRv6
 LAN End.X SID sub-TLV (Section 9.2 of [RFC9513]) in the case of IS-IS
 or OSPFv3, respectively.  The SRv6 LAN End.X SID TLV allows a node to
 announce the SRv6 SID corresponding to its adjacencies to all other
 (i.e., non-DIS or non-DR) nodes attached to the LAN in a single
 instance of the BGP-LS Link NLRI.  Without this TLV, multiple BGP-LS
 Link NLRIs would need to be originated, one for each neighbor, to
 advertise the SRv6 End.X SID TLVs for those non-DIS/non-DR neighbors.
 The SRv6 SID for these IGP adjacencies using the End.X behaviors
 (viz. End.X, End.X with PSP, End.X with USP, and End.X with PSP &
 USP) [RFC8986] are advertised using the SRv6 LAN End.X SID TLV.
 More than one instance of this TLV (one for each SRv6 LAN End.X SID)
 can be included in the BGP-LS Attribute.
 The BGP-LS IS-IS SRv6 LAN End.X SID and BGP-LS OSPFv3 SRv6 LAN End.X
 SID TLVs have the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Endpoint Behavior       |      Flags    |   Algorithm   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Weight    |   Reserved    |   Neighbor ID -               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
 | IS-IS System-ID (6 octets) or OSPFv3 Router-ID (4 octets)     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (16 octets) ...                                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Sub-TLVs (variable) . . .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 3: SRv6 LAN End.X SID TLV Format
 where:
 Type:  1107 for IS-IS and 1108 for OSPFv3
 Length:  variable
 Endpoint Behavior:  2-octet field.  The Endpoint behavior code point
    for this SRv6 SID as defined in Section 10.2 of [RFC8986].
 Flags:  1 octet of flags.  The flags are copied from the IS-IS SRv6
    LAN End.X SID sub-TLV (Section 8.2 of [RFC9352]) or the OSPFv3
    SRv6 LAN End.X SID sub-TLV (Section 9.2 of [RFC9513]) in the case
    of IS-IS or OSPFv3, respectively.
 Algorithm:  1-octet field.  Algorithm associated with the SID.
 Weight:  1-octet field.  The value represents the weight of the SID
    for the purpose of load balancing.
 Reserved:  1-octet field that MUST be set to 0 when originated and
    ignored on receipt.
 Neighbor ID:  6 octets of Neighbor System-ID in the IS-IS SRv6 LAN
    End.X SID TLV or 4 octets of Neighbor Router-ID in the OSPFv3 SRv6
    LAN End.X SID TLV.
 SID:  16-octet field.  This field encodes the advertised SRv6 SID as
    a 128-bit value.
 Sub-TLVs:  Used to advertise sub-TLVs that provide additional
    attributes for the specific SRv6 SID.  This document defines one
    in Section 8.

4.3. SRv6 Link MSD Types

 The Link MSD TLV [RFC8814] of the BGP-LS Attribute of the Link NLRI
 is also used to advertise the limits and the SRH operations supported
 on the specific link by the SRv6-capable node.  The SRv6 MSD types
 specified in Section 4 of [RFC9352] are also used with the BGP-LS
 Link MSD TLV, as these code points are shared between the IS-IS,
 OSPF, and BGP-LS protocols.  The description and semantics of these
 new MSD types for BGP-LS are identical as specified in [RFC9352].
 Each MSD type is encoded in the BGP-LS Link MSD TLV as a one-octet
 type followed by a one-octet value as derived from the IS-IS or
 OSPFv3 Link MSD advertisements specified in [RFC8814].

5. SRv6 Prefix Attributes

 SRv6 attributes with an IPv6 prefix are advertised using the BGP-LS
 Attribute TLVs defined in this section and associated with the BGP-LS
 Prefix NLRI.

5.1. SRv6 Locator TLV

 As specified in [RFC8986], an SRv6 SID comprises locator, function,
 and argument parts.
 A node is provisioned with one or more locators supported by that
 node.  Locators are covering prefixes for the set of SIDs provisioned
 on that node.  Each locator is advertised as a BGP-LS Prefix NLRI
 object along with the SRv6 Locator TLV in its BGP-LS Attribute.
 The information advertised via this TLV is derived from the IS-IS
 SRv6 Locator TLV (Section 7.1 of [RFC9352]) or the OSPFv3 SRv6
 Locator TLV (Section 7.1 of [RFC9513]) in the case of IS-IS or
 OSPFv3, respectively.
 The IPv6 Prefix matching the locator may also be advertised as prefix
 reachability by the underlying routing protocol.  In this case, the
 Prefix NLRI would also be associated with the Prefix Metric TLV
 [RFC7752] that carries the routing metric for this prefix.  A Prefix
 NLRI that has been advertised with a SRv6 Locator TLV is also
 considered a normal routing prefix (i.e., prefix reachability) only
 when there is also an IGP Metric TLV (TLV 1095) associated it.
 Otherwise, it is only considered an SRv6 Locator advertisement.
 The SRv6 Locator TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Flags    |   Algorithm   |           Reserved            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            Metric                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Sub-TLVs (variable) . . .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 4: SRv6 Locator TLV Format
 where:
 Type:  1162
 Length:  variable
 Flags:  1 octet of flags.  The flags are copied from the IS-IS SRv6
    Locator TLV (Section 7.1 of [RFC9352]) or the OSPFv3 SRv6 Locator
    TLV (Section 7.1 of [RFC9513]) in the case of IS-IS or OSPFv3,
    respectively.
 Algorithm:  1-octet field.  Algorithm associated with the SID.
 Reserved:  2-octet field.  The value MUST be set to 0 when originated
    and ignored on receipt.
 Metric:  4-octet field.  The value of the metric for the locator
    copied from the IS-IS SRv6 Locator TLV (Section 7.1 of [RFC9352])
    or the OSPFv3 SRv6 Locator TLV (Section 7.1 of [RFC9513]) in the
    case of IS-IS or OSPFv3, respectively.
 Sub-TLVs:  Used to advertise sub-TLVs that provide additional
    attributes for the given SRv6 Locator.  Currently, none are
    defined.

6. SRv6 SID NLRI

 The Link-State NLRI defined in [RFC7752] is extended to carry the
 SRv6 SID information.
 This document defines the following new Link-State NLRI type for SRv6
 SID information: SRv6 SID NLRI (type 6).
 The SRv6 SIDs associated with the node are advertised using the BGP-
 LS SRv6 SID NLRI.
 This new NLRI type 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
 +-+-+-+-+-+-+-+-+
 |  Protocol-ID  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Identifier                             |
 |                        (8 octets)                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Local Node Descriptors (variable)              //
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               SRv6 SID Descriptors (variable)                //
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     Figure 5: SRv6 SID NLRI Format
 where:
 Protocol-ID:  1-octet field that specifies the information source
    protocol [RFC7752].
 Identifier:  8-octet value as defined in [RFC7752].
 Local Node Descriptors TLV:  Set of Node Descriptor TLVs for the
    local node as defined in [RFC7752] for IGPs, the Direct Protocol-
    ID, and the Static configuration Protocol-ID or as defined in
    [RFC9086] for BGP.
 SRv6 SID Descriptors:  Set of SRv6 SID Descriptor TLVs.  This field
    MUST contain a single SRv6 SID Information TLV (Section 6.1) and
    MAY contain the Multi-Topology Identifier TLV [RFC7752].
 New TLVs for advertisement within the BGP-LS Attribute [RFC7752] are
 defined in Section 7 to carry the attributes of an SRv6 SID.

6.1. SRv6 SID Information TLV

 An SRv6 SID that is associated with the node and advertised using the
 SRv6 SID NLRI is encoded using the SRv6 SID Information TLV.
 When advertising the SRv6 SIDs from the IGPs, the SID information is
 derived from the IS-IS SRv6 End SID sub-TLV (Section 7.2 of
 [RFC9352]) or the OSPFv3 SRv6 End SID sub-TLV (Section 8 of
 [RFC9513]) in the case of IS-IS or OSPFv3, respectively.
 The TLV carries the SRv6 SIDs corresponding to the BGP PeerNode and
 PeerSet SIDs [RFC8402] when SRv6 BGP EPE functionality is enabled in
 BGP.
 The TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (16 octets) ...                                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    SID (cont ...)                                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 6: SRv6 SID Information TLV Format
 where:
 Type:  518
 Length:  16
 SID:  16-octet field.  This field encodes the advertised SRv6 SID as
    a 128-bit value.

7. SRv6 SID Attributes

 This section specifies the TLVs to be carried in the BGP Link State
 Attribute associated with the BGP-LS SRv6 SID NLRI.

7.1. SRv6 Endpoint Behavior TLV

 Each SRv6 SID instantiated on an SRv6-capable node has specific
 instructions (called "behavior") bound to it.  [RFC8986] describes
 how behaviors are bound to a SID and also defines the initial set of
 well-known behaviors.
 The SRv6 Endpoint Behavior TLV is a mandatory TLV that MUST be
 included in the BGP-LS Attribute associated with the BGP-LS SRv6 SID
 NLRI.
 When advertising the SRv6 SIDs from the IGPs, the Endpoint behavior,
 Flags, and Algorithm are derived from the IS-IS SRv6 End SID sub-TLV
 (Section 7.2 of [RFC9352]) or the OSPFv3 SRv6 End SID sub-TLV
 (Section 8 of [RFC9513]) in the case of IS-IS or OSPFv3,
 respectively.
 When advertising the SRv6 SIDs corresponding to the BGP EPE
 functionality, the Endpoint behavior corresponds to End.X and similar
 behaviors.  When advertising the SRv6 SIDs that are locally
 instantiated on the node using Direct as the Protocol-ID, the
 Endpoint behavior corresponds to any SRv6 Endpoint behavior
 associated with the node.  Flags are currently not defined.  The
 algorithm value MUST be 0 unless an algorithm is associated locally
 with the SRv6 Locator from which the SID is allocated.
 The TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Endpoint Behavior      |      Flags    |   Algorithm   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 7: SRv6 Endpoint Behavior TLV
 where:
 Type:  1250
 Length:  4
 Endpoint Behavior:  2-octet field.  The Endpoint behavior code point
    for this SRv6 SID.  Values are from the "SRv6 Endpoint Behaviors"
    IANA registry (Section 10.2 of [RFC8986]).
 Flags:  1 octet of flags.  The flags map to the IS-IS or OSPFv3
    encodings when advertising SRv6 SIDs corresponding to IGPs.  No
    flags are currently defined for SRv6 SIDs corresponding to BGP EPE
    or for advertisement of a SRv6 SID using Direct as the Protocol-
    ID.  Undefined flags MUST be set to 0 when originating and ignored
    on receipt.
 Algorithm:  1-octet field.  Algorithm associated with the SID.

7.2. SRv6 BGP PeerNode SID TLV

 The BGP PeerNode and PeerSet SIDs for SR-MPLS are specified in
 [RFC9086].  Similar Peer Node and Peer Set functionality can be
 realized with SRv6 using SIDs with END.X behavior.  Refer to
 Appendix A for some differences between the signaling of these SIDs
 in SR-MPLS and SRv6.  The SRv6 BGP PeerNode SID TLV is a mandatory
 TLV for use in the BGP-LS Attribute for an SRv6 SID NLRI advertised
 by BGP for the EPE functionality.  This TLV MUST be included along
 with SRv6 SIDs that are associated with the BGP PeerNode or PeerSet
 functionality.
 The TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Flags    |     Weight    |          Reserved             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Peer AS Number                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Peer BGP Identifier                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 8: SRv6 BGP PeerNode SID TLV Format
 where:
 Type:  1251
 Length:  12
 Flags:  1 octet of flags with the following definitions:
     0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |B|S|P|         |
    +-+-+-+-+-+-+-+-+
                 Figure 9: SRv6 BGP EPE SID Flags Format
    B-Flag:  Backup Flag.  If set, the SID is eligible to be protected
       using Fast Reroute (FRR).  The computation of the backup
       forwarding path and its association with the forwarding entry
       for the Peer BGP Identifier are implementation specific.
    S-Flag:  Set Flag.  When set, the S-Flag indicates that the SID
       refers to a set of BGP peering sessions (i.e., BGP Peer Set SID
       functionality) and therefore MAY be assigned to one or more
       End.X SIDs associated with BGP peering sessions.
    P-Flag:  Persistent Flag.  When set, the P-Flag indicates that the
       SID is persistently allocated, i.e., the value remains
       consistent across router restart and/or session flap.
    Other bits are reserved for future use and MUST be set to 0
    when originated and ignored on receipt.  The flags defined
    above are also used with the SRv6 End.X SID TLV when
    advertising the SRv6 BGP Peer Adjacency SID (Section 4.1).
 Weight:  1-octet field.  The value represents the weight of the SID
    for the purpose of load balancing.  The use of the weight is
    defined in [RFC8402].
 Reserved:  2-octet field.  The value MUST be set to 0 when originated
    and ignored on receipt.
 Peer AS Number:  4 octets of the BGP AS number of the peer router.
 Peer BGP Identifier:  4 octets of the BGP Identifier (BGP Router-ID)
    of the peer router.
 For an SRv6 BGP EPE PeerNode SID, one instance of this TLV is
 associated with the SRv6 SID.  For an SRv6 BGP EPE PeerSet SID,
 multiple instances of this TLV (one for each peer in the "peer set")
 are associated with the SRv6 SID and the S-Flag is set.

8. SRv6 SID Structure TLV

 The SRv6 SID Structure TLV is used to advertise the length of each
 individual part of the SRv6 SID as defined in [RFC8986].  It is an
 optional TLV for use in the BGP-LS Attribute for an SRv6 SID NLRI and
 as a sub-TLV of the SRv6 End.X SID, IS-IS SRv6 LAN End.X SID, and
 OSPFv3 SRv6 LAN End.X SID TLVs.
 When advertising SRv6 SIDs from the IGPs, the SRv6 SID Structure
 information is derived from the IS-IS SRv6 SID Structure sub-sub-TLV
 (Section 9 of [RFC9352]) or the OSPFv3 SRv6 SID Structure sub-TLV
 (Section 10 of [RFC9513]) in the case of IS-IS or OSPFv3,
 respectively.
 When advertising the SRv6 SIDs corresponding to the BGP EPE
 functionality or for advertising SRv6 SIDs using Direct as the
 Protocol-ID, the SRv6 SID Structure information is derived from the
 locally provisioned SRv6 SID.
 The TLV has the following format:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               Type            |          Length               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 10: SRv6 SID Structure TLV
 where:
 Type:  1252
 Length:  4
 LB Length:  1-octet field.  SRv6 SID Locator Block length in bits.
 LN Length:  1-octet field.  SRv6 SID Locator Node length in bits.
 Fun. Length:  1-octet field.  SRv6 SID Function length in bits.
 Arg. Length:  1-octet field.  SRv6 SID Argument length in bits.
 The sum of the LB Length, LN Length, Fun. Length, and Arg. Length
 MUST be less than or equal to 128.

9. IANA Considerations

 Per this document, IANA has allocated code points in the "Border
 Gateway Protocol - Link State (BGP-LS) Parameters" registry group, as
 described in the subsections below.

9.1. BGP-LS NLRI Types

 IANA has assigned the following code points in the "BGP-LS NLRI
 Types" registry:
                 +======+===============+===========+
                 | Type | NLRI Type     | Reference |
                 +======+===============+===========+
                 | 6    | SRv6 SID NLRI | RFC 9514  |
                 +------+---------------+-----------+
                   Table 1: Addition to BGP-LS NLRI
                            Types Registry

9.2. BGP-LS NLRI and Attribute TLVs

 IANA has assigned the following TLV code points in the "BGP-LS NLRI
 and Attribute TLVs" registry:
      +================+===========================+===========+
      | TLV Code Point | Description               | Reference |
      +================+===========================+===========+
      | 518            | SRv6 SID Information      | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1038           | SRv6 Capabilities         | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1106           | SRv6 End.X SID            | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1107           | IS-IS SRv6 LAN End.X SID  | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1108           | OSPFv3 SRv6 LAN End.X SID | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1162           | SRv6 Locator              | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1250           | SRv6 Endpoint Behavior    | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1251           | SRv6 BGP PeerNode SID     | RFC 9514  |
      +----------------+---------------------------+-----------+
      | 1252           | SRv6 SID Structure        | RFC 9514  |
      +----------------+---------------------------+-----------+
         Table 2: Additions to BGP-LS NLRI and Attribute TLVs
                               Registry

9.3. SRv6 BGP EPE SID Flags

 Per this document, IANA has created a new registry called "SRv6 BGP
 EPE SID Flags" under the "Border Gateway Protocol - Link State (BGP-
 LS) Parameters" registry group.  The allocation policy of this
 registry is "Standards Action" according to [RFC8126].
 The initial contents of the registry are as follows:
            +=====+==========================+===========+
            | Bit | Description              | Reference |
            +=====+==========================+===========+
            | 0   | Backup Flag (B-Flag)     | RFC 9514  |
            +-----+--------------------------+-----------+
            | 1   | Set Flag (S-Flag)        | RFC 9514  |
            +-----+--------------------------+-----------+
            | 2   | Persistent Flag (P-Flag) | RFC 9514  |
            +-----+--------------------------+-----------+
            | 3-7 | Unassigned               |           |
            +-----+--------------------------+-----------+
             Table 3: New SRv6 BGP EPE SID Flags Registry

10. Manageability Considerations

 This section is structured as recommended in [RFC5706].
 The new protocol extensions introduced in this document augment the
 existing IGP topology information that is distributed via [RFC7752].
 Procedures and protocol extensions defined in this document do not
 affect the BGP protocol operations and management other than as
 discussed in Section 6 (Manageability Considerations) of [RFC7752].
 Specifically, the malformed attribute tests for syntactic checks in
 Section 6.2.2 (Fault Management) of [RFC7752] now encompass the new
 BGP-LS extensions defined in this document.  The semantic or content
 checking for the TLVs specified in this document and their
 association with the BGP-LS NLRI types or their BGP-LS Attribute are
 left to the consumer of the BGP-LS information (e.g., an application
 or a controller) and not BGP.
 The SR information introduced in BGP-LS by this specification may be
 used by BGP-LS consumer applications like an SR Path Computation
 Engine (PCE) to learn the SRv6 capabilities of the nodes in the
 topology and the mapping of SRv6 segments to those nodes.  This can
 enable the SR PCE to perform path computations based on SR for
 traffic-engineering use cases and to steer traffic on paths different
 from the underlying IGP-based distributed best path computation.
 Errors in the encoding or decoding of the SRv6 information may result
 in the unavailability of such information to the SR PCE or incorrect
 information being made available to it.  This may result in the SR
 PCE not being able to perform the desired SR-based optimization
 functionality or performing it in an unexpected or inconsistent
 manner.  The handling of such errors by applications like SR PCE may
 be implementation specific and out of the scope of this document.
 The manageability considerations related to BGP EPE functionality are
 discussed in [RFC9086] in the context of SR-MPLS; they also apply to
 this document in the context of SRv6.
 The extensions specified in this document do not introduce any new
 configuration or monitoring aspects in BGP or BGP-LS other than as
 discussed in [RFC7752].  The manageability aspects of the underlying
 SRv6 features are covered by [SRV6-YANG].

11. Security Considerations

 The new protocol extensions introduced in this document augment the
 existing IGP topology information that is distributed via [RFC7752].
 The advertisement of the SRv6 link-state information defined in this
 document presents a similar risk as associated with the existing
 link-state information as described in [RFC7752].  Section 8
 (Security Considerations) of [RFC7752] also applies to these
 extensions.  The procedures and new TLVs defined in this document, by
 themselves, do not affect the BGP-LS security model discussed in
 [RFC7752].
 The extensions introduced in this document are used to propagate IGP-
 defined information [RFC9352] [RFC9513].  These extensions represent
 the advertisement of SRv6 information associated with the IGP node,
 link, and prefix.  The IGP instances originating these TLVs are
 assumed to support all the required security and authentication
 mechanisms (as described in [RFC9352] and [RFC9513]).
 The security considerations related to BGP EPE functionality are
 discussed in [RFC9086] in the context of SR-MPLS, and they also apply
 to this document in the context of SRv6.
 BGP-LS SRv6 extensions enable traffic-engineering use cases within
 the SR domain.  SR operates within a trusted domain [RFC8402], and
 its security considerations also apply to BGP-LS sessions when
 carrying SR information.  The SR traffic-engineering policies using
 the SIDs advertised via BGP-LS are expected to be used entirely
 within this trusted SR domain (e.g., between multiple AS or IGP
 domains within a single provider network).  Therefore, precaution is
 necessary to ensure that the link-state information (including SRv6
 information) advertised via BGP-LS sessions is securely limited to
 consumers within this trusted SR domain.  BGP peering sessions for
 address families other than Link State may be set up to routers
 outside the SR domain.  The isolation of BGP-LS peering sessions is
 RECOMMENDED to ensure that BGP-LS topology information (including the
 newly added SR information) is not advertised to an external BGP
 peering session outside the SR domain.

12. References

12.1. 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>.
 [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
            S. Ray, "North-Bound Distribution of Link-State and
            Traffic Engineering (TE) Information Using BGP", RFC 7752,
            DOI 10.17487/RFC7752, March 2016,
            <https://www.rfc-editor.org/info/rfc7752>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [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>.
 [RFC8814]  Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
            and N. Triantafillis, "Signaling Maximum SID Depth (MSD)
            Using the Border Gateway Protocol - Link State", RFC 8814,
            DOI 10.17487/RFC8814, August 2020,
            <https://www.rfc-editor.org/info/rfc8814>.
 [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>.
 [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>.
 [RFC9352]  Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
            and Z. Hu, "IS-IS Extensions to Support Segment Routing
            over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
            February 2023, <https://www.rfc-editor.org/info/rfc9352>.
 [RFC9513]  Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
            "OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)",
            RFC 9513, DOI 10.17487/RFC9513, December 2023,
            <https://www.rfc-editor.org/info/rfc9513>.

12.2. Informative References

 [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
            Management of New Protocols and Protocol Extensions",
            RFC 5706, DOI 10.17487/RFC5706, November 2009,
            <https://www.rfc-editor.org/info/rfc5706>.
 [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>.
 [SRV6-YANG]
            Raza, S., Agarwal, S., Liu, X., Hu, Z., Hussain, I., Shah,
            H. C., Voyer, D., Matsushima, S., Horiba, K.,
            Rajamanickam, J., and A. Abdelsalam, "YANG Data Model for
            SRv6 Base and Static", Work in Progress, Internet-Draft,
            draft-ietf-spring-srv6-yang-02, 23 September 2022,
            <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
            srv6-yang-02>.

Appendix A. Differences with BGP-EPE for SR-MPLS

 The signaling of SRv6 SIDs corresponding to BGP-EPE functionality as
 defined in this document differs from the signaling of SR-MPLS BGP-
 EPE SIDs as specified in [RFC9086].  This section provides a high-
 level overview of the same.
 There is no difference in the advertisement of the BGP Peer Adjacency
 SID in both SR-MPLS and SRv6, and it is advertised as an attribute of
 the Link NLRI, which identifies a specific Layer 3 interface on the
 BGP Speaker.  The difference is in the advertisement of the BGP
 PeerNode and PeerSet SIDs.
 In the case of SR-MPLS, an additional Link NLRI is required to be
 advertised corresponding to each BGP peering session on the node.
 Note that this is not the same Link NLRI associated with the actual
 Layer 3 interface even when the peering is set up using the interface
 IP addresses.  These BGP-LS Link NLRIs are not really links in the
 conventional link-state routing data model but instead identify BGP
 peering sessions.  The BGP PeerNode and/or PeerSet SIDs associated
 with that peering session are advertised as attributes associated
 with this peering Link NLRI.  In the case of SRv6, each BGP PeerNode
 or PeerSet SID is considered to be associated with the BGP Speaker
 Node and is advertised using the BGP-LS SRv6 SID NLRI, while the
 peering session information is advertised as attributes associated
 with it.
 The advertisement of the BGP PeerSet SID for SR-MPLS is done by
 including that SID as an attribute in all the Link NLRIs
 corresponding to the peering sessions that are part of the "set".
 The advertisement of the BGP PeerSet SID for SRv6 is advertised using
 a single SRv6 SID NLRI, and all the peers associated with that "set"
 are indicated as attributes associated with the NLRI.

Acknowledgements

 The authors would like to thank Peter Psenak, Arun Babu, Pablo
 Camarillo, Francois Clad, Peng Shaofu, Cheng Li, Dhruv Dhody, Tom
 Petch, and Dan Romascanu for their review of this document and their
 comments.  The authors would also like to thank Susan Hares for her
 shepherd review and Adrian Farrel for his detailed Routing Area
 Directorate review.

Contributors

 James Uttaro
 AT&T
 United States of America
 Email: ju1738@att.com
 Hani Elmalky
 Ericsson
 United States of America
 Email: hani.elmalky@gmail.com
 Arjun Sreekantiah
 Individual
 United States of America
 Email: arjunhrs@gmail.com
 Les Ginsberg
 Cisco Systems
 United States of America
 Email: ginsberg@cisco.com
 Shunwan Zhuang
 Huawei
 China
 Email: zhuangshunwan@huawei.com

Authors' Addresses

 Gaurav Dawra
 LinkedIn
 United States of America
 Email: gdawra.ietf@gmail.com
 Clarence Filsfils
 Cisco Systems
 Belgium
 Email: cfilsfil@cisco.com
 Ketan Talaulikar (editor)
 Cisco Systems
 India
 Email: ketant.ietf@gmail.com
 Mach(Guoyi) Chen
 Huawei
 China
 Email: mach.chen@huawei.com
 Daniel Bernier
 Bell Canada
 Canada
 Email: daniel.bernier@bell.ca
 Bruno Decraene
 Orange
 France
 Email: bruno.decraene@orange.com
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