Inter-Domain Routing

Internet Engineering Task Force (IETF)                        S. Previdi
Internet-Draft
Request for Comments: 9085                           Huawei Technologies
Intended status:
Category: Standards Track                             K. Talaulikar, Ed.
Expires: December 29, 2019
ISSN: 2070-1721                                              C. Filsfils
                                                     Cisco Systems, Inc.
                                                              H. Gredler
                                                            RtBrick Inc.
                                                                 M. Chen
                                                     Huawei Technologies
                                                           June 27, 2019

             BGP Link-State extensions
                                                             August 2021

  Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment
                                Routing
              draft-ietf-idr-bgp-ls-segment-routing-ext-16

Abstract

   Segment Routing (SR) allows for a flexible definition of end-to-end
   paths by encoding paths as sequences of topological sub-paths, subpaths, called
   "segments".  These segments are advertised by routing protocols e.g. protocols,
   e.g., by the link state link-state routing protocols (IS-IS, OSPFv2 OSPFv2, and OSPFv3)
   within IGP topologies.

   This document defines extensions to the BGP Link-state address-family Border Gateway Protocol -
   Link State (BGP-LS) address family in order to carry segment routing SR information
   via BGP.

Status of This Memo

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   https://www.rfc-editor.org/info/rfc9085.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language
   2.  BGP-LS Extensions for Segment Routing . . . . . . . . . . . .   5
     2.1.  Node Attributes Attribute TLVs  . . . . . . . . . . . . . . . . . .   5
       2.1.1.  SID/Label TLV . . . . . . . . . . . . . . . . . . . .   5
       2.1.2.  SR Capabilities TLV . . . . . . . . . . . . . . . . .   6
       2.1.3.  SR Algorithm  SR-Algorithm TLV  . . . . . . . . . . . . . . . . . .   8
       2.1.4.  SR Local Block TLV  . . . . . . . . . . . . . . . . .   8
       2.1.5.  SRMS Preference TLV . . . . . . . . . . . . . . . . .  10
     2.2.  Link Attribute TLVs . . . . . . . . . . . . . . . . . . .  11
       2.2.1.  Adjacency SID TLV . . . . . . . . . . . . . . . . . .  11
       2.2.2.  LAN Adjacency SID TLV . . . . . . . . . . . . . . . .  12
       2.2.3.  L2 Bundle Member Attribute Attributes TLV  . . . . . . . . . . .  14
     2.3.  Prefix Attribute TLVs . . . . . . . . . . . . . . . . . .  16
       2.3.1.  Prefix SID  Prefix-SID TLV  . . . . . . . . . . . . . . . . . . .  17
       2.3.2.  Prefix Attribute Flags TLV  . . . . . . . . . . . . .  18
       2.3.3.  Source Router Identifier (Source Router-ID) TLV . . .  19
       2.3.4.  Source OSPF Router-ID TLV
       2.3.5.  Range TLV . . . . . . . . . . . . . . . . . . . . . .  19
     2.4.  Equivalent IS-IS Segment Routing TLVs/Sub-TLVs  . . . . .  21
     2.5.  Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs  .  22
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
     3.1.  TLV/Sub-TLV Code Points Summary . . . . . . . . . . . . .  25
   4.  Manageability Considerations  . . . . . . . . . . . . . . . .  25
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  27
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     8.1.
   4.  Manageability Considerations
   5.  Security Considerations
   6.  References
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  28
     8.2.
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  30
   Acknowledgements
   Contributors
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   Segment Routing (SR) allows for a flexible definition of end-to-end
   paths by combining sub-paths subpaths called "segments".  A segment can
   represent any instruction: topological or service-based. service based.  A segment
   can have a local semantic to an SR node or global semantic within a
   domain.  Within IGP topologies, an SR path is encoded as a sequence
   of topological sub-paths, subpaths, called "IGP segments".  These segments are
   advertised by the link-state routing protocols (IS-IS, OSPFv2 OSPFv2, and
   OSPFv3).

   [RFC8402] defines the Link-State link-state IGP segments - Prefix, Node, Anycast -- prefix, node,
   anycast, and Adjacency adjacency segments.  Prefix segments, by default,
   represent an ECMP-aware shortest-path to a prefix, as per the state
   of the IGP topology.  Adjacency segments represent a hop over a
   specific adjacency between two nodes in the IGP.  A prefix segment is
   typically a multi-hop path while an adjacency segment, in most of the
   cases, is a one-hop path.  Node and anycast segments are variations
   of the prefix segment with their specific characteristics.

   When Segment Routing SR is enabled in an IGP domain, segments are advertised in the
   form of Segment Identifiers (SIDs).  The IGP link-
   state link-state routing
   protocols have been extended to advertise SIDs and other SR-related
   information.  IGP extensions are described for: IS-
   IS [I-D.ietf-isis-segment-routing-extensions], IS-IS [RFC8667],
   OSPFv2
   [I-D.ietf-ospf-segment-routing-extensions] [RFC8665], and OSPFv3
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. [RFC8666].  Using these extensions, Segment Routing SR
   can be enabled within an IGP domain.

   Segment Routing (SR)

   SR allows advertisement of single or multi-hop paths.  The flooding
   scope for the IGP extensions for Segment routing SR is IGP area-wide.  Consequently,
   the contents of a Link State Link-State Database (LSDB) or a Traffic Engineering
   Database (TED) has the scope of an IGP area and area; therefore, by using the
   IGP alone alone, it is not enough to construct segments across multiple IGP Area
   area or AS Autonomous System (AS) boundaries.

   In order to address the need for applications that require
   topological visibility across IGP areas, or even across Autonomous
   Systems (AS), ASes, the
   BGP-LS address-family/sub-address-family address family / subaddress family have been defined to allow
   BGP to carry Link-State link-state information.  The BGP Network Layer
   Reachability Information (NLRI) encoding format for BGP-LS and a new
   BGP Path Attribute called the BGP-LS attribute "BGP-LS Attribute" are defined in
   [RFC7752].  The identifying key of each Link-State link-state object, namely a
   node, link, or prefix, is encoded in the NLRI NLRI, and the properties of
   the object are encoded in the BGP-LS attribute. Attribute.

                           +------------+
                           |  Consumer  |
                           +------------+
                                 ^
                                 |
                                 v
                       +-------------------+
                       |    BGP Speaker    |         +-----------+
                       | (Route-Reflector) (Route Reflector) |         | Consumer  |
                       +-------------------+         +-----------+
                             ^   ^   ^                       ^
                             |   |   |                       |
             +---------------+   |   +-------------------+   |
             |                   |                       |   |
             v                   v                       v   v
       +-----------+       +-----------+             +-----------+
       |    BGP    |       |    BGP    |             |    BGP    |
       |  Speaker  |       |  Speaker  |    . . .    |  Speaker  |
       +-----------+       +-----------+             +-----------+
             ^                   ^                         ^
             |                   |                         |
            IGP                 IGP                       IGP

                Figure 1: Link State info collection Link-State Information Collection

   Figure 1 denotes a typical deployment scenario.  In each IGP area,
   one or more nodes are configured with BGP-LS.  These BGP speakers
   form an IBGP Internal BGP (IBGP) mesh by connecting to one or more route-reflectors. route
   reflectors.  This way, all BGP speakers (specifically the route-reflectors) route
   reflectors) obtain
   Link-State link-state information from all IGP areas (and
   from other ASes from
   EBGP External BGP (EBGP) peers).  An external
   component connects to the route-reflector route reflector to obtain this information
   (perhaps moderated by a policy regarding what information is or isn't
   advertised to the external component) as described in [RFC7752].

   This document describes extensions to BGP-LS to advertise the SR
   information.  An external component (e.g., a controller) can collect
   SR information from across an SR domain (as described in [RFC8402])
   and construct the end-to-end path (with its associated SIDs) that
   need
   needs to be applied to an incoming packet to achieve the desired end-
   to-end forwarding.  SR operates within a trusted domain consisting of
   a single AS or multiple ASes managed by the same administrative entity
   e.g.
   entity, e.g., within a single provider network.

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 Segment Routing

   This document defines SR extensions to BGP-LS and specifies the TLVs
   and sub-TLVs for advertising SR information within the BGP-LS
   Attribute.  Section  Sections 2.4 and Section 2.5 lists list the equivalent TLVs and
   sub-TLVs sub-
   TLVs in the IS-IS, OSPFv2 OSPFv2, and OSPFv3 protocols.

   BGP-LS [RFC7752] defines the BGP-LS NLRI that can be a Node NLRI, a
   Link NLRI NLRI, or a Prefix NLRI.  BGP-LS [RFC7752] NLRI, and it defines the TLVs that map link-state link-
   state information to BGP-LS NLRI within the BGP-LS Attribute.  This
   document adds additional BGP-LS Attribute TLVs in order to encode SR
   information.  It does not introduce any changes to the encoding of
   the BGP-LS NLRIs.

2.1.  Node Attributes Attribute TLVs

   The following Node Attribute TLVs are defined:

                +------+-----------------+---------------+

                +======+=================+===============+
                | Type | Description     | Section       |
                +------+-----------------+---------------+
                +======+=================+===============+
                | 1161 | SID/Label       | Section 2.1.1 |
                +------+-----------------+---------------+
                | 1034 | SR Capabilities | Section 2.1.2 |
                +------+-----------------+---------------+
                | 1035 | SR Algorithm    | Section 2.1.3 |
                +------+-----------------+---------------+
                | 1036 | SR Local Block  | Section 2.1.4 |
                +------+-----------------+---------------+
                | 1037 | SRMS Preference | Section 2.1.5 |
                +------+-----------------+---------------+

                       Table 1: Node Attribute TLVs

   These TLVs should only be added to the BGP-LS Attribute associated
   with the Node NLRI describing that describes the IGP node that is originating
   the corresponding IGP TLV/sub-TLV described below.

2.1.1.  SID/Label TLV

   The SID/Label TLV is used as a sub-TLV by the SR Capabilities
   (Section 2.1.2) and Segment Routing Local Block (SRLB)
   (Section 2.1.4) TLVs.  This information is derived from the protocol protocol-
   specific advertisements.

   o

   *  IS-IS, as defined by the SID/Label sub-TLV Sub-TLV in section Section 2.3 of
      [I-D.ietf-isis-segment-routing-extensions].

   o
      [RFC8667].

   *  OSPFv2/OSPFv3, as defined by the SID/Label sub-TLV Sub-TLV in section Section 2.1
      of [I-D.ietf-ospf-segment-routing-extensions] [RFC8665] and section Section 3.1 of
      [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. [RFC8666].

   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/Label (variable)                    //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: SID/Label TLV Format

   Where:

   Type:  1161

   Length:  Variable.  Either 3 or 4 octets depending on whether the
      value is encoded as a label or as an index/SID.

   SID/Label:  If the length is set to 3, then the 20 rightmost bits
      represent a label (the total TLV size is 7) 7), and the 4 leftmost
      bits are set to 0.  If the length is set to 4, then the value
      represents a 32 bit 32-bit SID (the total TLV size is 8).

2.1.2.  SR Capabilities TLV

   The SR Capabilities TLV is used in order to advertise the node's SR
   Capabilities
   capabilities including its Segment Routing Global Base (SRGB)
   range(s).  In the case of IS-IS, the capabilities also include the
   IPv4 and IPv6 support for the SR-MPLS forwarding plane.  This
   information is derived from the protocol specific protocol-specific advertisements.

   o

   *  IS-IS, as defined by the SR Capabilities sub-TLV SR-Capabilities Sub-TLV in section Section 3.1 of
      [I-D.ietf-isis-segment-routing-extensions].

   o
      [RFC8667].

   *  OSPFv2/OSPFv3, as defined by the SID/Label Range TLV in section
      Section 3.2 of [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].  OSPFv3 leverages the same TLV as
      defined for OSPFv2.

   The SR 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    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Range Size 1                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                SID/Label sub-TLV Sub-TLV 1                           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ...

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Range Size N                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                SID/Label sub-TLV Sub-TLV N                           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: SR Capabilities TLV Format

   Where:

   Type:  1034

   Length:  Variable.  Minimum  The minimum length is 12. 12 octets.

   Flags:  1 octet of flags as defined in section Section 3.1 of
      [I-D.ietf-isis-segment-routing-extensions] [RFC8667] for
      IS-IS.  The flags are not currently defined for OSPFv2 and OSPFv3
      and MUST be set to 0 and ignored on receipt.

   Reserved:  1 octet that MUST be set to 0 and ignored on receipt.

   One or more entries, each of which have the following format:

      Range Size:  3 octet octets with a non-zero value indicating the number
         of labels in the range.

      SID/Label TLV TLV:  (as defined in Section 2.1.1) used as sub-TLV a sub-TLV,
         which encodes the first label in the range.  Since the SID/
         Label TLV is used to indicate the first label of the SRGB
         range, only label encoding is valid under the SR Capabilities
         TLV.

2.1.3.  SR Algorithm  SR-Algorithm TLV

   The SR Algorithm SR-Algorithm TLV is used in order to advertise the SR Algorithms algorithms
   supported by the node.  This information is derived from the protocol
   specific
   protocol-specific advertisements.

   o

   *  IS-IS, as defined by the SR-Algorithm sub-TLV Sub-TLV in section Section 3.2 of
      [I-D.ietf-isis-segment-routing-extensions].

   o
      [RFC8667].

   *  OSPFv2/OSPFv3, as defined by the SR-Algorithm TLV in section Section 3.1
      of [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].  OSPFv3 leverages the same TLV as defined for
      OSPFv2.

   The SR Algorithm SR-Algorithm 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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Algorithm 1  |  Algorithm... |  Algorithm N  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 4: SR Algorithm SR-Algorithm TLV Format

   Where:

   Type:  1035

   Length:  Variable.  Minimum  The minimum length is 1 octet and the maximum can
      be 256.

   Algorithm:  One or more fields of 1 octet each identifying that identifies the
      algorithm.

2.1.4.  SR Local Block TLV

   The SR Local Block (SRLB) SRLB TLV contains the range(s) of labels the node has reserved
   for local SIDs.  Local SIDs are used, e.g., in IGP (IS-IS, OSPF) for Adjacency-SIDs,
   Adjacency SIDs and may also be allocated by components other than IGP
   protocols.  As an example, an application or a controller may
   instruct a node to allocate a specific local SID.  Therefore, in
   order for such applications or controllers to know the range of local
   SIDs available, it is required that the node
   advertises is required to advertise its SRLB.

   This information is derived from the protocol specific protocol-specific
   advertisements.

   o

   *  IS-IS, as defined by the SR Local Block sub-TLV SRLB Sub-TLV in section Section 3.3 of
      [I-D.ietf-isis-segment-routing-extensions].

   o [RFC8667].

   *  OSPFv2/OSPFv3, as defined by the SR Local Block TLV in section
      3.3. Section 3.3
      of [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].  OSPFv3 leverages the same TLV as defined for
      OSPFv2.

   The SRLB 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    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Sub-Range Size 1                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                SID/Label sub-TLV Sub-TLV 1                           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ...

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Sub-Range Size N                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                SID/Label sub-TLV Sub-TLV N                           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 5: SRLB TLV Format

   Where:

   Type:  1036

   Length:  Variable.  Minimum  The minimum length is 12. 12 octets.

   Flags:  1 octet of flags.  The flags are as defined in section Section 3.3 of [I-D.ietf-isis-segment-routing-extensions]
      [RFC8667] for IS-IS.  The flags are not currently defined for
      OSPFv2 and OSPFv3 and MUST be set to 0 and ignored on receipt.

   Reserved:  1 octet that MUST be set to 0 and ignored on receipt.

   One or more entries corresponding to a sub-range(s), each of which
   have the following format:

      Range Size: 3 octet  3-octet value indicating the number of labels in the
         range.

      SID/Label TLV TLV:  (as defined in Section 2.1.1) used as sub-TLV a sub-TLV,
         which encodes the first label in the sub-range.  Since the SID/
         Label TLV is used to indicate the first label of the SRLB sub-
         range, only label encoding is valid under the SR Local Block
         TLV.

2.1.5.  SRMS Preference TLV

   The Segment Routing Mapping Server (SRMS) Preference TLV is used in
   order to associate a preference with SRMS advertisements from a
   particular source.  [I-D.ietf-spring-segment-routing-ldp-interop]  [RFC8661] specifies the SRMS functionality along
   with the SRMS preference of the node advertising the SRMS Prefix-to-SID Mapping Prefix-to-
   SID mapping ranges.

   This information is derived from the protocol specific protocol-specific
   advertisements.

   o

   *  IS-IS, as defined by the SRMS Preference sub-TLV Sub-TLV in section Section 3.4 of
      [I-D.ietf-isis-segment-routing-extensions].

   o
      [RFC8667].

   *  OSPFv2/OSPFv3, as defined by the SRMS Preference TLV in section
      Section 3.4 of [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].  OSPFv3 leverages the same TLV as
      defined for OSPFv2.

   The SRMS Preference 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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Preference    |
   +-+-+-+-+-+-+-+-+

                    Figure 6: SRMS Preference TLV Format

   Where:

   Type:  1037

   Length: 1.  1 octet

   Preference:  1 octet carrying an unsigned 8 bit 8-bit SRMS preference.

2.2.  Link Attribute TLVs

   The following Link Attribute TLVs are are defined:

             +------+-----------------------+---------------+

        +======+=================================+===============+
        | Type | Description                     | Section       |
             +------+-----------------------+---------------+
        +======+=================================+===============+
        | 1099 | Adjacency SID TLV               | Section 2.2.1 |
        +------+---------------------------------+---------------+
        | 1100 | LAN Adjacency SID TLV           | Section 2.2.2 |
        +------+---------------------------------+---------------+
        | 1172 | L2 Bundle Member Attributes TLV | Section 2.2.3 |
             +------+-----------------------+---------------+
        +------+---------------------------------+---------------+

                       Table 2: Link Attribute TLVs

   These TLVs should only be added to the BGP-LS Attribute associated
   with the Link NLRI describing that describes the link of the IGP node that is
   originating the corresponding IGP TLV/sub-TLV described below.

2.2.1.  Adjacency SID TLV

   The Adjacency SID TLV is used in order to advertise information
   related to an Adjacency SID.  This information is derived from Adj-
   SID sub-TLV the
   Adj-SID Sub-TLV of IS-IS (section (Section 2.2.1 of
   [I-D.ietf-isis-segment-routing-extensions]), [RFC8667]), OSPFv2 (section
   (Section 6.1 of
   [I-D.ietf-ospf-segment-routing-extensions]) [RFC8665]), and OSPFv3 (section (Section 7.1 of [I-D.ietf-ospf-ospfv3-segment-routing-extensions]). [RFC8666]).

   The Adjacency SID 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          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   SID/Label/Index (variable)                 //
   +---------------------------------------------------------------+

                     Figure 7: Adjacency SID TLV Format

   Where:

   Type:  1099

   Length:  Variable.  Either 7 or 8 octets depending on Label the label or Index
      index encoding of the SID

      Flags. 1 octet SID.

   Flags:  1-octet value which that should be set as:

      *  IS-IS Adj-SID flags are as defined in section Section 2.2.1 of
         [I-D.ietf-isis-segment-routing-extensions]. [RFC8667].

      *  OSPFv2 Adj-SID flags are as defined in section Section 6.1 of
         [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].

      *  OSPFv3 Adj-SID flags are as defined in section Section 7.1 of
         [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. [RFC8666].

   Weight:  1 octet carrying the weight used for load-balancing
      purposes.  The use of weight is described in section Section 3.4 of
      [RFC8402].

   Reserved:  2 octets that MUST be set to 0 and ignored on receipt.

   SID/Index/Label:

      *

      IS-IS:  Label or index value as defined in section Section 2.2.1 of
         [I-D.ietf-isis-segment-routing-extensions].

      *
         [RFC8667].

      OSPFv2:  Label or index value as defined in section Section 6.1 of
         [I-D.ietf-ospf-segment-routing-extensions].

      *
         [RFC8665].

      OSPFv3:  Label or index value as defined in section Section 7.1 of
         [I-D.ietf-ospf-ospfv3-segment-routing-extensions].
         [RFC8666].

   The Flags and, as an extension, the SID/Index/Label fields of this
   TLV are interpreted according to the respective underlying IS-IS,
   OSPFv2
   OSPFv2, or OSPFv3 protocol.  The Protocol-ID of the BGP-LS Link NLRI
   is used to determine the underlying protocol specification for
   parsing these fields.

2.2.2.  LAN Adjacency SID TLV

   For a LAN, normally a node only announces its adjacency to the IS-IS
   pseudo-node
   pseudonode (or the equivalent OSPF Designated and Backup Designated
   Routers).  The LAN Adjacency Segment SID TLV allows a node to announce
   adjacencies to all other nodes attached to the LAN in a single
   instance of the BGP-LS Link NLRI.  Without this TLV, the
   corresponding BGP-LS link Link NLRI would need to be originated for each
   additional adjacency in order to advertise the SR TLVs for these
   neighbor adjacencies.

   This information is derived from the LAN-Adj-SID sub-TLV Sub-TLV of IS-IS
   (section
   (Section 2.2.2 of [I-D.ietf-isis-segment-routing-extensions]) and [RFC8667]), the LAN Adj-SID sub-TLV Sub-TLV of OSPFv2 (section
   (Section 6.2 of
   [I-D.ietf-ospf-segment-routing-extensions]) [RFC8665]), and the LAN Adj-SID Sub-TLV of OSPFv3 (section
   (Section 7.2 of [I-D.ietf-ospf-ospfv3-segment-routing-extensions]). [RFC8666]).

   The LAN Adjacency SID 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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             OSPF Neighbor ID / IS-IS System-ID System ID                |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    SID/Label/Index (variable)                //
   +---------------------------------------------------------------+

                   Figure 8: LAN Adjacency SID TLV Format

   Where:

   Type:  1100

   Length:  Variable.  For IS-IS IS-IS, it would be 13 or 14 octets depending
      on
      Label the label or Index index encoding of the SID.  For OSPF OSPF, it would be
      11 or 12 octets depending on Label the label or Index index encoding of the
      SID.

      Flags. 1 octet

   Flags:  1-octet value which that should be set as:

      *  IS-IS LAN Adj-SID flags are as defined in section Section 2.2.2 of
         [I-D.ietf-isis-segment-routing-extensions].
         [RFC8667].

      *  OSPFv2 LAN Adj-SID flags are as defined in section Section 6.2 of
         [I-D.ietf-ospf-segment-routing-extensions].
         [RFC8665].

      *  OSPFv3 LAN Adj-SID flags are as defined in section Section 7.2 of
         [I-D.ietf-ospf-segment-routing-extensions].
         [RFC8666].

   Weight:  1 octet carrying the weight used for load-balancing
      purposes.  The use of weight is described in section Section 3.4 of
      [RFC8402].

   Reserved:  2 octets that MUST be set to 0 and ignored on receipt.

   Neighbor ID:  6 octets for IS-IS for the System-ID System ID, and 4 octets for
      OSPF for the OSPF Router-ID of the neighbor.

   SID/Index/Label:

      *

      IS-IS:  Label or index value as defined in section Section 2.2.2 of
         [I-D.ietf-isis-segment-routing-extensions].

      *
         [RFC8667].

      OSPFv2:  Label or index value as defined in section Section 6.2 of
         [I-D.ietf-ospf-segment-routing-extensions].

      *
         [RFC8665].

      OSPFv3:  Label or index value as defined in section Section 7.2 of
         [I-D.ietf-ospf-ospfv3-segment-routing-extensions].
         [RFC8666].

   The Neighbor ID, Flags Flags, and, as an extension, the SID/Index/Label
   fields of this TLV are interpreted according to the respective
   underlying IS-IS, OSPFv2 OSPFv2, or OSPFv3 protocol.  The Protocol-ID of the
   BGP-LS Link NLRI is used to determine the underlying protocol
   specification for parsing these fields.

2.2.3.  L2 Bundle Member Attribute Attributes TLV

   The L2 Bundle Member Attribute Attributes TLV identifies an L2 Bundle Member
   link
   link, which in turn is associated with a parent L3 link.  The L3 link
   is described by the Link NLRI defined in [RFC7752] [RFC7752], and the L2 Bundle
   Member Attribute Attributes TLV is associated with the Link NLRI.  The TLV MAY
   include sub-TLVs which that describe attributes associated with the bundle
   member.  The identified bundle member represents a unidirectional
   path from the originating router to the neighbor specified in the
   parent L3 Link. link.  Multiple L2 Bundle Member Attribute Attributes TLVs MAY be
   associated with a Link NLRI.

   This information is derived from L2 Bundle Member Attributes TLV of
   IS-IS (section (Section 2 of [I-D.ietf-isis-l2bundles]). [RFC8668]).  The equivalent functionality has not
   been specified as yet for OSPF.

   The L2 Bundle Member Attribute Attributes 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               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     L2 Bundle Member Descriptor               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Link attribute sub-TLVs(variable) Attribute Sub-TLVs(variable)          //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 9: L2 Bundle Member Attributes TLV Format

   Where:

   Type:  1172

   Length:  Variable.

   L2 Bundle Member Descriptor: 4 octets  4-octet field that carries a Link
      Local Identifier link-local
      identifier as defined in [RFC4202].

   Link attributes for L2 Bundle Member Links links are advertised as sub-TLVs
   of the L2 Bundle Member Attribute Attributes TLV.  The sub-TLVs are identical
   to existing BGP-LS TLVs as identified in the table below.

   +-------------+------------------------------------+----------------+

    +================+==========================+====================+
    | TLV Code Point | Description              | Reference      |
   |    Point    |                                    | Document |
   +-------------+------------------------------------+----------------+
    +================+==========================+====================+
    |      1088      | Administrative group (color)     | [RFC7752]          |
    |                | (color)                  |                    |
    +----------------+--------------------------+--------------------+
    |      1089      | Maximum link bandwidth   | [RFC7752]          |
    +----------------+--------------------------+--------------------+
    |      1090      | Max. reservable link bandwidth     | [RFC7752]          |
    |                | bandwidth                |                    |
    +----------------+--------------------------+--------------------+
    |      1091      | Unreserved bandwidth     | [RFC7752]          |
    +----------------+--------------------------+--------------------+
    |      1092      | TE default metric        | [RFC7752]          |
    +----------------+--------------------------+--------------------+
    |      1093      | Link protection type     | [RFC7752]          |
    +----------------+--------------------------+--------------------+
    |      1099      | Adjacency Segment Identifier (Adj-        | Section 2.2.1      |
    |                | SID) Identifier (Adj-SID) TLV |                    |
    +----------------+--------------------------+--------------------+
    |      1100      | LAN Adjacency Segment Identifier    | Section 2.2.2      |
    |                | Identifier (Adj-SID) TLV |                    |
    +----------------+--------------------------+--------------------+
    |      1114      | Unidirectional link delay      | [RFC8571]          |
    |                | delay                    |                    |
    +----------------+--------------------------+--------------------+
    |      1115      | Min/Max Unidirectional   | [RFC8571]          |
    |                | link delay               | [RFC8571]                    |
    +----------------+--------------------------+--------------------+
    |      1116      | Unidirectional Delay Variation     | [RFC8571]          |
    |                | Variation                |                    |
    +----------------+--------------------------+--------------------+
    |      1117      | Unidirectional packet loss Link Loss | [RFC8571]          |
    +----------------+--------------------------+--------------------+
    |      1118      | Unidirectional residual bandwidth  | [RFC8571]          |
    |                | bandwidth                |                    |
    +----------------+--------------------------+--------------------+
    |      1119      | Unidirectional available bandwidth | [RFC8571]          |
    |                | bandwidth                |                    |
    +----------------+--------------------------+--------------------+
    |      1120      | Unidirectional bandwidth Utilized  | [RFC8571]          |
    |                | utilization Bandwidth                |                    |
   +-------------+------------------------------------+----------------+
    +----------------+--------------------------+--------------------+

       Table 3: BGP-LS Attribute TLVs are also used as sub-TLVs of
                   the L2 Bundle Member Attribute Attributes TLV

2.3.  Prefix Attribute TLVs

   The following Prefix Attribute TLVs are defined:

             +------+------------------------+---------------+

            +======+==========================+===============+
            | Type | Description              | Section       |
             +------+------------------------+---------------+
            +======+==========================+===============+
            | 1158 | Prefix SID Prefix-SID               | Section 2.3.1 |
            +------+--------------------------+---------------+
            | 1159 | Range                    | Section 2.3.4 2.3.5 |
            +------+--------------------------+---------------+
            | 1170 | Prefix Attribute Flags   | Section 2.3.2 |
            +------+--------------------------+---------------+
            | 1171 | Source Router-ID Router Identifier | Section 2.3.3 |
             +------+------------------------+---------------+
            +------+--------------------------+---------------+
            | 1174 | Source OSPF Router-ID    | Section 2.3.4 |
            +------+--------------------------+---------------+

                       Table 4: Prefix Attribute TLVs

   These TLVs should only be added to the BGP-LS Attribute associated
   with the Prefix NLRI describing that describes the prefix of the IGP node that
   is originating the corresponding IGP TLV/sub-TLV described below.

2.3.1.  Prefix SID  Prefix-SID TLV

   The Prefix SID Prefix-SID TLV is used in order to advertise information related
   to a Prefix SID. Prefix-SID.  This information is derived from the Prefix-SID sub-TLV
   Sub-TLV of IS-IS (section (Section 2.1 of [I-D.ietf-isis-segment-routing-extensions])
   and [RFC8667]), the Prefix SID sub-TLV Prefix-SID Sub-TLV
   of OSPFv2 (section (Section 5 of
   [I-D.ietf-ospf-segment-routing-extensions]) [RFC8665]), and the Prefix-SID Sub-TLV of
   OSPFv3 (section (Section 6 of
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]). [RFC8666]).

   The Prefix SID Prefix-SID 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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       SID/Index/Label (variable)             //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 10: Prefix SID Prefix-SID TLV Format

   Where:

   Type:  1158

   Length:  Variable. 7 or 8 octets depending on Label the label or Index index
      encoding of the SID SID.

   Flags: 1 octet  1-octet value which that should be set as:

      *  IS-IS Prefix SID Prefix-SID flags are as defined in section Section 2.1.1 of
         [I-D.ietf-isis-segment-routing-extensions].
         [RFC8667].

      *  OSPFv2 Prefix SID Prefix-SID flags are as defined in section Section 5 of
         [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].

      *  OSPFv3 Prefix SID Prefix-SID flags are as defined in section Section 6 of
         [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].

   Algorithm: 1 octet  1-octet value identify identifies the algorithm.  The semantics of
      the algorithm are described in section Section 3.1.1 of [RFC8402].

   Reserved:  2 octets that MUST be set to 0 and ignored on receipt.

   SID/Index/Label:

      *

      IS-IS:  Label or index value as defined in section Section 2.1 of
         [I-D.ietf-isis-segment-routing-extensions].

      *
         [RFC8667].

      OSPFv2:  Label or index value as defined in section Section 5 of
         [I-D.ietf-ospf-segment-routing-extensions].

      *
         [RFC8665].

      OSPFv3:  Label or index value as defined in section Section 6 of
         [I-D.ietf-ospf-ospfv3-segment-routing-extensions].
         [RFC8666].

   The Flags and, as an extension, the SID/Index/Label fields of this
   TLV are interpreted according to the respective underlying IS-IS,
   OSPFv2
   OSPFv2, or OSPFv3 protocol.  The Protocol-ID of the BGP-LS Prefix
   NLRI is used to determine the underlying protocol specification for
   parsing these fields.

2.3.2.  Prefix Attribute Flags TLV

   The Prefix Attribute Flags TLV carries IPv4/IPv6 prefix attribute
   flags information.  These flags are defined for OSPFv2 in section Section 2.1
   of [RFC7684], for OSPFv3 in section Appendix A.4.1.1 of [RFC5340] [RFC5340], and for IS-
   IS IS-IS in section
   Section 2.1 of [RFC7794].

   The Prefix Attribute Flags 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 (variable)                      //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 11: Prefix Attribute Flags TLV Format

   Where:

   Type:  1170

   Length:  Variable.

   Flags:  a variable length flag variable-length Flag field (according to the length Length field).
      Flags are routing protocol specific and are to be set as below:

      *  IS-IS flags correspond to the IPv4/IPv6 Extended Reachability
         Attribute Flags defined in section Section 2.1 of [RFC7794] [RFC7794].  In the
         case of the X-flag when associated with IPv6 prefix
         reachability, the setting corresponds to the setting of the
         X-flag in the fixed format of IS-IS TLVs 236 [RFC5308] and 237
         [RFC5120].

      *  OSPFv2 flags correspond to the Flags field of the OSPFv2
         Extended Prefix TLV defined in section Section 2.1 of [RFC7684] [RFC7684].

      *  OSPFv3 flags map to the Prefix Options field defined in section
         Appendix A.4.1.1 of [RFC5340] and extended in section Section 3.1 of [RFC8362]
         [RFC8362].

   The Flags field of this TLV is interpreted according to the
   respective underlying IS-IS, OSPFv2 OSPFv2, or OSPFv3 protocol.  The
   Protocol-ID of the BGP-LS Prefix NLRI is used to determine the
   underlying protocol specification for parsing this field.

2.3.3.  Source Router Identifier (Source Router-ID) TLV

   The Source Router-ID Router Identifier TLV contains the IPv4 or IPv6 Router-ID Router
   Identifier of the originator of the Prefix. prefix.  For the IS-IS protocol protocol,
   this is derived from the IPv4/IPv6 Source Router ID sub-TLV Sub-TLV as
   defined in section Section 2.2 of [RFC7794].  For the OSPF protocol, this is
   derived from the Prefix Source Router Address Sub-TLV as defined in
   Section 2.2 of [RFC9084].

   The Source Router Identifier 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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   4- or 16-octet Router Identifier           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 12: Source Router Identifier TLV Format

   Where:

   Type:  1171

   Length:  Variable. 4 or 16 octets for the IPv4 or IPv6 prefix,
      respectively.

   Router-ID:  the IPv4 or IPv6 Router-ID in the case of IS-IS, and the
      IPv4 or IPv6 Router Address in the case of OSPF.

2.3.4.  Source OSPF Router-ID TLV

   The Source OSPF Router-ID TLV is applicable only for the OSPF
   protocol and contains the OSPF Router-ID of the originator of the
   prefix.  It is derived from the Prefix Source OSPF Router-ID sub-TLV Sub-TLV
   as defined in section 4 Section 2.1 of
   [I-D.ietf-lsr-ospf-prefix-originator]. [RFC9084].

   The Source OSPF Router-ID 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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   4 or 16 octet                    4-octet OSPF Router-ID                    //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 12: 13: Source OSPF Router-ID TLV Format

   Where:

   Type: 1171  1174

   Length: Variable.  4 or 16 in case of IS-IS and 4 in case of OSPF. octets

   OSPF Router-ID:  the IPv4 or IPv6 OSPF Router-ID in case of IS-IS and the
      OSPF Router-ID in node originating the case of OSPF.

2.3.4.
      prefix.

2.3.5.  Range TLV

   The Range TLV is used in order to advertise a range of prefix-to-SID
   mappings as part of the Segment Routing Mapping Server (SRMS) SRMS functionality [I-D.ietf-spring-segment-routing-ldp-interop], [RFC8661], as defined in
   the respective underlying IGP SR extensions
   [I-D.ietf-ospf-segment-routing-extensions] (section 4),
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions] (section 5) and
   [I-D.ietf-isis-segment-routing-extensions] (section 2.4). extensions: Section 4 of [RFC8665],
   Section 5 of [RFC8666], and Section 2.4 of [RFC8667].  The
   information advertised in the Range TLV is derived from the SID/Label
   Binding TLV in the case of IS-IS and the OSPFv2/OSPFv3 Extended
   Prefix Range TLV in the case of OSPFv2/OSPFv3.

   A Prefix NLRI, that has been advertised with a Range TLV, is
   considered a normal routing prefix (i.e. (i.e., prefix reachability) only
   when there is also an IGP metric TLV (TLV 1095) associated it.
   Otherwise, it is considered only as the first prefix in the range for
   prefix-to-SID mapping advertisement.

   The format of the Range 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     | Reserved      |             Range Size        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           sub-TLVs                           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 13: 14: Range TLV Format

   Where:

   Type:  1159

   Length:  Variable. 11 or 12 octets depending on Label the label or Index index
      encoding of the SID SID.

   Flags: 1 octet  1-octet value which that should be set as:

      *  IS-IS SID/Label Binding TLV flags are as defined in section Section 2.4.1
         of [I-D.ietf-isis-segment-routing-extensions]. [RFC8667].

      *  OSPFv2 OSPF Extended Prefix Range TLV flags are as defined in
         section
         Section 4 of [I-D.ietf-ospf-segment-routing-extensions]. [RFC8665].

      *  OSPFv3 Extended Prefix Range TLV flags are as defined in section Section 5
         of [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. [RFC8666].

   Reserved:  1 octet that MUST be set to 0 and ignored on receipt.

   Range Size:  2 octets that carry the number of prefixes that are
      covered by the advertisement.. advertisement.

   The Flags field of this TLV is interpreted according to the
   respective underlying IS-IS, OSPFv2 OSPFv2, or OSPFv3 protocol.  The
   Protocol-ID of the BGP-LS Prefix NLRI is used to determine the
   underlying protocol specification for parsing this field.

   The prefix-to-SID mappings are advertised using sub-TLVs as below:

   IS-IS:
      SID/Label Range TLV
         Prefix-SID sub-TLV Sub-TLV

   OSPFv2/OSPFv3:
      OSPFv2/OSPFv3 Extended Prefix Range TLV
           Prefix SID sub-TLV
         Prefix-SID Sub-TLV

   BGP-LS:
      Range TLV
         Prefix-SID TLV (used as a sub-TLV in this context)

   The prefix-to-SID mapping information for the BGP-LS Prefix-SID TLV
   (used as a sub-TLV in this context) is encoded as described in
   Section 2.3.1.

2.4.  Equivalent IS-IS Segment Routing TLVs/Sub-TLVs

   This section illustrate illustrates the IS-IS Segment Routing Extensions TLVs
   and sub-TLVs mapped to the ones defined in this document.

   The following table, illustrates for

   For each BGP-LS TLV, the following table illustrates its equivalence
   in IS-IS.

   +------------+---------------+--------------------------------------+

   +========================+==============================+===========+
   | Descriptio Description            | IS-IS TLV TLV/sub-TLV            | Reference |
   | n          | /sub-TLV      |                                      |
   +------------+---------------+--------------------------------------+
   +========================+==============================+===========+
   | SR Capabil | SR-           | [I-D.ietf-isis-segment-routing-exten |
   | ities      | Capabilities        | sions]                               |
   |            | sub-TLV SR-Capabilities Sub-TLV (2)  | [RFC8667] |
   +------------------------+------------------------------+-----------+
   | SR         | SR-Algorithm  | [I-D.ietf-isis-segment-routing-exten |
   | Algorithm           | sub-TLV SR-Algorithm Sub-TLV (19)    | sions] [RFC8667] |
   +------------------------+------------------------------+-----------+
   | SR Local Block         | SR Local      | [I-D.ietf-isis-segment-routing-exten |
   | Block      | Block sub-TLV | sions]                               |
   |            | Sub-TLV (22)  | [RFC8667] |
   +------------------------+------------------------------+-----------+
   | SRMS       | SRMS          | [I-D.ietf-isis-segment-routing-exten |
   | Preference        | SRMS Preference    | sions]                               |
   |            | sub-TLV Sub-TLV (19) | [RFC8667] |
   +------------------------+------------------------------+-----------+
   | Adjacency  | Adj-SID sub-  | [I-D.ietf-isis-segment-routing-exten |
   | SID          | TLV Adj-SID Sub-TLV (31)         | sions] [RFC8667] |
   +------------------------+------------------------------+-----------+
   | LAN        | LAN-Adj-SID   | [I-D.ietf-isis-segment-routing-exten |
   | Adjacency  | sub-TLV (32)  | sions]                               |
   | SID      | LAN-Adj-SID Sub-TLV (32)     | [RFC8667] |
   | Prefix SID
   +------------------------+------------------------------+-----------+
   | Prefix-SID             | [I-D.ietf-isis-segment-routing-exten |
   |            | sub-TLV Prefix-SID Sub-TLV (3)       | sions] [RFC8667] |
   +------------------------+------------------------------+-----------+
   | Range                  | SID/Label     | [I-D.ietf-isis-segment-routing-exten |
   |            | Binding TLV   | sions]                               |
   |            | (149)  | [RFC8667] |
   +------------------------+------------------------------+-----------+
   | SID/Label              | SID/Label     | [I-D.ietf-isis-segment-routing-exten |
   |            | sub-TLV Sub-TLV (1)        | sions] [RFC8667] |
   +------------------------+------------------------------+-----------+
   | Prefix Attribute       | Prefix        | [RFC7794]                            |
   | Attribute  | Attributes    |                                      |
   | Flags      | Flags sub-TLV Sub-  | [RFC7794] |
   | Flags                  | TLV (4)                      |           |
   +------------------------+------------------------------+-----------+
   | Source Router          | IPv4/IPv6     | [RFC7794]                            |
   | Router-ID  | Source Router |                                      |
   |            | ID sub-TLV   | [RFC7794] |
   | Identifier             | Sub-TLV (11/12)              |           |
   +------------------------+------------------------------+-----------+
   | L2 Bundle Member       | L2 Bundle     | [I-D.ietf-isis-l2bundles]            |
   | Member     | Member        |                                      |
   | Attributes | Attributes  | [RFC8668] |
   | Attributes             | TLV (25)                     |           |
   +------------+---------------+--------------------------------------+
   +------------------------+------------------------------+-----------+

          Table 5: IS-IS Segment Routing Extensions TLVs/Sub-TLVs

2.5.  Equivalent OSPFv2/OSPFv3 Segment Routing TLVs/Sub-TLVs

   This section illustrate illustrates the OSPFv2 and OSPFv3 Segment Routing
   Extensions TLVs and sub-TLVs mapped to the ones defined in this
   document.

   The following table, illustrates for

   For each BGP-LS TLV, the following tables illustrate its equivalence
   in OSPFv2 and OSPFv3.

   +------------+-------------+----------------------------------------+

       +===================+==========================+===========+
       | Descriptio Description       | OSPFv2 TLV TLV/sub-TLV       | Reference |
   | n          | /sub-TLV    |                                        |
   +------------+-------------+----------------------------------------+
       +===================+==========================+===========+
       | SR Capabil Capabilities   | SID/Label   | [I-D.ietf-ospf-segment-routing-extensi |
   | ities      | Range TLV   | ons]                                   |
   |            | (9)  | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | SR         | SR-         | [I-D.ietf-ospf-segment-routing-extensi |
   | Algorithm  | Algorithm      | ons]                                   |
   |            | SR-Algorithm TLV (8)     | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | SR Local Block    | SR Local    | [I-D.ietf-ospf-segment-routing-extensi |
   | Block      | Block TLV   | ons]                                   |
   |            | (14)  | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | SRMS       | SRMS        | [I-D.ietf-ospf-segment-routing-extensi |
   | Preference   | SRMS Preference  | ons]                                   |
   |            | TLV (15) | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | Adjacency  | Adj-SID     | [I-D.ietf-ospf-segment-routing-extensi |
   | SID     | sub-TLV Adj-SID Sub-TLV (2)      | ons] [RFC8665] |
       +-------------------+--------------------------+-----------+
       | LAN Adjacency SID | LAN Adj-SID | [I-D.ietf-ospf-segment-routing-extensi |
   | Adjacency  | sub-TLV Sub-TLV (3)  | ons]                                   |
   | SID        |             |                                        |
   | Prefix SID | Prefix SID  | [I-D.ietf-ospf-segment-routing-extensi [RFC8665] |
       +-------------------+--------------------------+-----------+
       | Prefix-SID        | sub-TLV Prefix-SID Sub-TLV (2)   | ons] [RFC8665] |
       +-------------------+--------------------------+-----------+
       | Range             | OSPF        | [I-D.ietf-ospf-segment-routing-extensi |
   |            | Extended    | ons]                                   |
   |            | Prefix     | [RFC8665] |
       |                   | Range TLV   |                                        |
   |            | (2)            |           |
       +-------------------+--------------------------+-----------+
       | SID/Label         | SID/Label   | [I-D.ietf-ospf-segment-routing-extensi |
   |            | sub-TLV Sub-TLV (1)    | ons] [RFC8665] |
       +-------------------+--------------------------+-----------+
       | Prefix Attribute  | Flags of    | [RFC7684]                              |
   | Attribute  | OSPFv2      |                                        |
   | Flags      | Extended | [RFC7684] |
       | Flags             | Prefix TLV  |                                        |
   |            | (1)           |           |
       +-------------------+--------------------------+-----------+
       | Source Router     | Prefix      | [I-D.ietf-lsr-ospf-prefix-originator]  |
   | Router-ID  | Source Router     | [RFC9084] |
       | Identifier        | Router-ID Address Sub-TLV (5)      |           |
       +-------------------+--------------------------+-----------+
       | Source OSPF       | sub-TLV Prefix Source OSPF       | [RFC9084] |
       | Router-ID         | (TBD) Router-ID Sub-TLV (4)    |           |
   +------------+-------------+----------------------------------------+
       +-------------------+--------------------------+-----------+

         Table 6: OSPFv2 Segment Routing Extensions TLVs/Sub-TLVs
   +-----------+------------+------------------------------------------+

       +===================+==========================+===========+
       | Descripti Description       | OSPFv3 TLV TLV/sub-TLV       | Reference |
   | on        | /sub-TLV   |                                          |
   +-----------+------------+------------------------------------------+
       +===================+==========================+===========+
       | SR Capabi Capabilities   | SID/Label  | [I-D.ietf-ospf-segment-routing-extension |
   | lities    | Range TLV  | s]                                       |
   |           | (9)  | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | SR        | SR-        | [I-D.ietf-ospf-segment-routing-extension |
   | Algorithm | Algorithm      | s]                                       |
   |           | SR-Algorithm TLV (8)     | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | SR Local Block    | SR Local   | [I-D.ietf-ospf-segment-routing-extension |
   | Block     | Block TLV  | s]                                       |
   |           | (14)  | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | SRMS Pref Preference   | SRMS       | [I-D.ietf-ospf-segment-routing-extension |
   | erence    | Preference | s]                                       |
   |           | TLV (15) | [RFC8665] |
       +-------------------+--------------------------+-----------+
       | Adjacency | Adj-SID    | [I-D.ietf-ospf-ospfv3-segment-routing-ex |
   | SID     | sub-TLV    | tensions]                                |
   |           | Adj-SID Sub-TLV (5)      | [RFC8666] |
       +-------------------+--------------------------+-----------+
       | LAN       | LAN Adj-   | [I-D.ietf-ospf-ospfv3-segment-routing-ex |
   | Adjacency | SID sub-   | tensions]                                |
   | SID | TLV LAN Adj-SID Sub-TLV (6)  | [RFC8666] |
       +-------------------+--------------------------+-----------+
       | Prefix    | Prefix SID | [I-D.ietf-ospf-ospfv3-segment-routing-ex |
   | SID       | sub-TLV    | tensions]                                |
   | Prefix-SID        | Prefix-SID Sub-TLV (4)   | [RFC8666] |
       +-------------------+--------------------------+-----------+
       | Range             | OSPFv3     | [I-D.ietf-ospf-ospfv3-segment-routing-ex |
   |           | Extended   | tensions]                                |
   |           | Prefix   | [RFC8666] |
       |                   | Range TLV  |                                          |
   |           | (9)            |           |
       +-------------------+--------------------------+-----------+
       | SID/Label         | SID/Label  | [I-D.ietf-ospf-ospfv3-segment-routing-ex |
   |           | sub-TLV    | tensions]                                |
   |           | Sub-TLV (7)    | [RFC8666] |
       +-------------------+--------------------------+-----------+
       | Prefix    | Prefix     | [RFC8362]                                |
   | Attribute  | Prefix Option     |                                          |
   | Flags     | Fields of  | [RFC8362] |
       | Flags             | Prefix TLV |                                          |
   |           | types      |                                          |
   |           | types 3,5,6   |           |
       +-------------------+--------------------------+-----------+
       | Source OSPF       | Prefix     | [I-D.ietf-lsr-ospf-prefix-originator]    |
   | Router-ID | Source Router     | [RFC9084] |
       | Router Identifier | Router-ID Address Sub-TLV (28)     |           |
       +-------------------+--------------------------+-----------+
       | Source OSPF       | sub-TLV Prefix Source OSPF       | [RFC9084] |
       | Router-ID         | (TBD) Router-ID Sub-TLV (27)   |           |
   +-----------+------------+------------------------------------------+
       +-------------------+--------------------------+-----------+

         Table 7: OSPFv3 Segment Routing Extensions TLVs/Sub-TLVs

3.  IANA Considerations

   Early allocation of codepoints has been done by

   IANA for this
   document from has registered the following code points in the registry "BGP-LS Node
   Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs"
   registry under the "BGP-LS Parameters" "Border Gateway Protocol - Link State (BGP-LS)
   Parameter" registry based on Table 8.  The column "IS-IS TLV/Sub-TLV"
   defined in the registry does not require any value and should be left
   empty.

3.1.  TLV/Sub-TLV Code Points Summary

   This section contains the global table of all TLVs/sub-TLVs defined
   in this document.

     +----------------+-----------------------------+---------------+

     +================+=============================+===============+
     | TLV Code Point | Description                 | Reference     |
     +----------------+-----------------------------+---------------+
     +================+=============================+===============+
     |      1034      | SR Capabilities             | Section 2.1.2 |
     +----------------+-----------------------------+---------------+
     |      1035      | SR Algorithm                | Section 2.1.3 |
     +----------------+-----------------------------+---------------+
     |      1036      | SR Local Block              | Section 2.1.4 |
     +----------------+-----------------------------+---------------+
     |      1037      | SRMS Preference             | Section 2.1.5 |
     +----------------+-----------------------------+---------------+
     |      1099      | Adjacency SID               | Section 2.2.1 |
     +----------------+-----------------------------+---------------+
     |      1100      | LAN Adjacency SID           | Section 2.2.2 |
     +----------------+-----------------------------+---------------+
     |      1158      | Prefix SID Prefix-SID                  | Section 2.3.1 |
     +----------------+-----------------------------+---------------+
     |      1159      | Range                       | Section 2.3.4 2.3.5 |
     +----------------+-----------------------------+---------------+
     |      1161      | SID/Label                   | Section 2.1.1 |
     +----------------+-----------------------------+---------------+
     |      1170      | Prefix Attribute Flags      | Section 2.3.2 |
     +----------------+-----------------------------+---------------+
     |      1171      | Source Router-ID Router Identifier    | Section 2.3.3 |
     +----------------+-----------------------------+---------------+
     |      1172      | L2 Bundle Member Attributes | Section 2.2.3 |
     +----------------+-----------------------------+---------------+
     |      1174      | Source OSPF Router-ID       | Section 2.3.4 |
     +----------------+-----------------------------+---------------+

               Table 8: Summary Table of TLV/Sub-TLV Codepoints Code Points

4.  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 the Manageability Considerations section of [RFC7752].
   Specifically, the malformed attribute tests for syntactic checks in
   the Fault Management section of [RFC7752] now encompass the new BGP-
   LS Attribute TLVs 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 is
   left to the consumer of the BGP-LS information (e.g. (e.g., an application
   or a controller) and not the BGP protocol.

   A consumer of the BGP-LS information retrieves this information over
   a BGP-LS session (refer Section to Sections 1 and 2 of [RFC7752]).  The
   handling of semantic or content errors by the consumer would be
   dictated by the nature of its application usage and hence is beyond
   the scope of this document.

   This document only introduces new Attribute TLVs TLVs, and any syntactic
   error in them would result in only that specific attribute the BGP-LS Attribute being discarded
   with an error log.  The SR information introduced in BGP-LS by this specification,
   specification may be used by BGP-LS consumer applications like a an SR path computation engine
   Path Computation Engine (PCE) to learn the SR capabilities of the
   nodes in the topology and the mapping of SR segments to those nodes.
   This can enable the SR PCE to perform path computations based on SR
   for traffic engineering use-cases use cases and to steer traffic on paths
   different from the underlying IGP based IGP-based distributed best path best-path
   computation.  Errors in the encoding or decoding of the SR
   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 SR-
   based optimization functionality or to perform it in an unexpected or
   inconsistent manner.  The handling of such errors by applications
   like SR PCE may be implementation specific and out of scope of this
   document.

   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
   SR features are covered by [I-D.ietf-spring-sr-yang],
   [I-D.ietf-isis-sr-yang] [RFC9020], [ISIS-SR-YANG], and [I-D.ietf-ospf-sr-yang].
   [OSPF-SR-YANG].

5.  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 SR link attribute information defined in
   this document presents similar risk as associated with the existing
   set of link attribute information as described in [RFC7752].  The
   Security Considerations section 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 TLVs introduced in this document are used to propagate IGP IGP-
   defined information ([I-D.ietf-isis-segment-routing-extensions],
   [I-D.ietf-ospf-segment-routing-extensions] (see [RFC8665], [RFC8666], and
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]). [RFC8667]).  These
   TLVs represent the SR information associated with the IGP node, link link,
   and prefix.  The IGP instances originating these TLVs are assumed to
   support all the required security and authentication mechanisms (as
   described in [I-D.ietf-isis-segment-routing-extensions],
   [I-D.ietf-ospf-segment-routing-extensions] [RFC8665], [RFC8666], and
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]) [RFC8667]) in order to prevent
   any security issue when propagating the TLVs into BGP-LS.

   BGP-LS SR extensions enable traffic engineering use-cases use cases within the
   Segment Routing
   SR domain.  SR operates within a trusted domain
   [RFC8402] [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. (e.g., between multiple AS/
   domains ASes/domains within a
   single provider network).  Therefore, precaution is necessary to
   ensure that the link-state information (including SR information)
   advertised via BGP-LS sessions is limited to consumers
   in a secure manner within this trusted SR domain.  BGP peering
   sessions for address-families other than Link-State may be setup 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.

8.  References

8.1.  Normative References

   [I-D.ietf-isis-l2bundles]
              Ginsberg, L., Bashandy, A., Filsfils, C., Nanduri, M., and
              E. Aries, "Advertising L2 Bundle Member Link Attributes in
              IS-IS", draft-ietf-isis-l2bundles-07 (work in progress),
              May 2017.

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., and B. Decraene, "IS-IS Extensions for
              Segment Routing", draft-ietf-isis-segment-routing-
              extensions-25 (work in progress), May 2019.

   [I-D.ietf-lsr-ospf-prefix-originator]
              Wang, A., Lindem, A., Dong, J., Talaulikar, K., and P.
              Psenak, "OSPF Extension for Prefix Originator", draft-
              ietf-lsr-ospf-prefix-originator-00 (work in progress),
              February 2019.

   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
              Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment
              Routing", draft-ietf-ospf-ospfv3-segment-routing-
              extensions-23 (work in progress), January 2019.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-27 (work via BGP-LS sessions is limited to consumers in progress), December 2018. a secure
   manner 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.

6.  References

6.1.  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>.

   [RFC4202]  Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
              <https://www.rfc-editor.org/info/rfc4202>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <https://www.rfc-editor.org/info/rfc5308>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [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>.

   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <https://www.rfc-editor.org/info/rfc7794>.

   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [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>.

   [RFC8571]  Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
              C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
              IGP Traffic Engineering Performance Metric Extensions",
              RFC 8571, DOI 10.17487/RFC8571, March 2019,
              <https://www.rfc-editor.org/info/rfc8571>.

8.2.

   [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>.

   [RFC8668]  Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
              M., and E. Aries, "Advertising Layer 2 Bundle Member Link
              Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
              December 2019, <https://www.rfc-editor.org/info/rfc8668>.

   [RFC9084]  Wang, A., Lindem, A., Dong, J., Psenak, P., and K.
              Talaulikar, Ed., "OSPF Prefix Originator Extensions",
              RFC 9084, DOI 10.17487/RFC9084, August 2021,
              <https://www.rfc-editor.org/info/rfc9084>.

6.2.  Informative References

   [I-D.ietf-isis-sr-yang]

   [ISIS-SR-YANG]
              Litkowski, S., Qu, Y., Sarkar, P., Chen, I., and J.
              Tantsura, "YANG Data Model for IS-IS Segment Routing",
              draft-ietf-isis-sr-yang-05 (work
              Work in progress), March 2019.

   [I-D.ietf-ospf-sr-yang] Progress, Internet-Draft, draft-ietf-isis-sr-yang-
              10, 21 February 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-isis-sr-
              yang-10>.

   [OSPF-SR-YANG]
              Yeung, D., Qu, Y., Zhang, Z., J., Chen, I., and A. Lindem,
              "YANG Data Model for OSPF SR (Segment Routing) Protocol",
              draft-ietf-ospf-sr-yang-07 (work
              Work in progress), March 2019.

   [I-D.ietf-spring-segment-routing-ldp-interop] Progress, Internet-Draft, draft-ietf-ospf-sr-yang-
              15, 2 July 2021, <https://datatracker.ietf.org/doc/html/
              draft-ietf-ospf-sr-yang-15>.

   [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>.

   [RFC8661]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., and S. Litkowski, "Segment Routing interworking MPLS
              Interworking with LDP",
              draft-ietf-spring-segment-routing-ldp-interop-15 (work in
              progress), September 2018.

   [I-D.ietf-spring-sr-yang] RFC 8661, DOI 10.17487/RFC8661,
              December 2019, <https://www.rfc-editor.org/info/rfc8661>.

   [RFC9020]  Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
              Tantsura, "YANG Data Model for Segment Routing", draft-
              ietf-spring-sr-yang-12 (work in progress), February 2019.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions", RFC 5706, 9020,
              DOI 10.17487/RFC5706, November 2009,
              <https://www.rfc-editor.org/info/rfc5706>.

7. 10.17487/RFC9020, May 2021,
              <https://www.rfc-editor.org/info/rfc9020>.

Acknowledgements

   The authors would like to thank Jeffrey Haas, Aijun Wang, Robert
   Raszuk
   Raszuk, and Susan Hares for their review of this document and their
   comments.  The authors would also like to thank Alvaro Retana for his
   extensive review and comments comments, which helped correct issues and
   improve the document.

6.

Contributors

   The following people have substantially contributed to the editing of
   this document:

   Peter Psenak
   Cisco Systems

   Email: ppsenak@cisco.com

   Les Ginsberg
   Cisco Systems

   Email: ginsberg@cisco.com

   Acee Lindem
   Cisco Systems

   Email: acee@cisco.com

   Saikat Ray
   Individual

   Email: raysaikat@gmail.com

   Jeff Tantsura
   Apstra Inc.

   Email: jefftant.ietf@gmail.com

Authors' Addresses

   Stefano Previdi
   Huawei Technologies
   Rome
   Italy

   Email: stefano@previdi.net

   Ketan Talaulikar (editor)
   Cisco Systems, Inc.
   India

   Email: ketant@cisco.com

   Clarence Filsfils
   Cisco Systems, Inc.
   Brussels
   Belgium

   Email: cfilsfil@cisco.com

   Hannes Gredler
   RtBrick Inc.

   Email: hannes@rtbrick.com

   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Building, No. 156 Beiqing Rd.
   Beijing
   100095
   China

   Email: mach.chen@huawei.com