



Inter-Domain Routing                                          S. Previdi
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                      K. Talaulikar, Ed.
Expires: December 29, 2019                                   C. Filsfils
                                                     Cisco Systems, Inc.
                                                              H. Gredler
                                                            RtBrick Inc.
                                                                 M. Chen
                                                     Huawei Technologies
                                                           June 27, 2019


             BGP Link-State 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, called
   "segments".  These segments are advertised by routing protocols e.g.
   by the link state routing protocols (IS-IS, OSPFv2 and OSPFv3) within
   IGP topologies.

   This document defines extensions to the BGP Link-state address-family
   in order to carry segment routing information via BGP.

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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on December 29, 2019.

Copyright Notice

   Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  BGP-LS Extensions for Segment Routing . . . . . . . . . . . .   5
     2.1.  Node Attributes TLVs  . . . . . . . . . . . . . . . . . .   5
       2.1.1.  SID/Label TLV . . . . . . . . . . . . . . . . . . . .   5
       2.1.2.  SR Capabilities TLV . . . . . . . . . . . . . . . . .   6
       2.1.3.  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 TLV  . . . . . . . . . . .  14
     2.3.  Prefix Attribute TLVs . . . . . . . . . . . . . . . . . .  16
       2.3.1.  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.  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.  Normative References  . . . . . . . . . . . . . . . . . .  28
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30



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1.  Introduction

   Segment Routing (SR) allows for a flexible definition of end-to-end
   paths by combining sub-paths called "segments".  A segment can
   represent any instruction: topological or 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, called "IGP segments".  These segments are
   advertised by the link-state routing protocols (IS-IS, OSPFv2 and
   OSPFv3).

   [RFC8402] defines the Link-State IGP segments - Prefix, Node, Anycast
   and 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 is enabled in an IGP domain, segments are
   advertised in the form of Segment Identifiers (SIDs).  The IGP 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], OSPFv2
   [I-D.ietf-ospf-segment-routing-extensions] and OSPFv3
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions].  Using these
   extensions, Segment Routing can be enabled within an IGP domain.

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

   In order to address the need for applications that require
   topological visibility across IGP areas, or even across Autonomous
   Systems (AS), the BGP-LS address-family/sub-address-family have been
   defined to allow BGP to carry 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 are
   defined in [RFC7752].  The identifying key of each Link-State object,
   namely a node, link, or prefix, is encoded in the NLRI and the
   properties of the object are encoded in the BGP-LS attribute.






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

                   Figure 1: Link State info 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 mesh by connecting to one or more route-reflectors.
   This way, all BGP speakers (specifically the route-reflectors) obtain
   Link-State information from all IGP areas (and from other ASes from
   EBGP peers).  An external component connects to the 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 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 or multiple ASes managed by the same administrative entity
   e.g. within a single provider network.








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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 2.4 and Section 2.5 lists the equivalent TLVs and
   sub-TLVs in IS-IS, OSPFv2 and OSPFv3 protocols.

   BGP-LS [RFC7752] defines the BGP-LS NLRI that can be a Node NLRI, a
   Link NLRI or a Prefix NLRI.  BGP-LS [RFC7752] defines the TLVs that
   map 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 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 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
   specific advertisements.

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

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




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   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 depending whether the value is
      encoded as a label or as an index/SID.

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

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

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

   The SR Capabilities TLV has the following format:










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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Type            |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Flags    |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   ...

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


                   Figure 3: SR Capabilities TLV Format

   Where:

      Type: 1034

      Length: Variable.  Minimum length is 12.

      Flags: 1 octet of flags as defined in section 3.1 of
      [I-D.ietf-isis-segment-routing-extensions] 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 with a non-zero value indicating the number
         of labels in the range.

         SID/Label TLV (as defined in Section 2.1.1) used as 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.



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2.1.3.  SR Algorithm TLV

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

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

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

   The 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 TLV Format

   Where:

      Type: 1035

      Length: Variable.  Minimum length is 1 and maximum can be 256.

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

2.1.4.  SR Local Block TLV

   The SR Local Block (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, 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 its SRLB.

   This information is derived from the protocol specific
   advertisements.



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

   o  OSPFv2/OSPFv3, as defined by the SR Local Block TLV in section
      3.3. of [I-D.ietf-ospf-segment-routing-extensions].  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 1                           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ...

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


                         Figure 5: SRLB TLV Format

   Where:

      Type: 1036

      Length: Variable.  Minimum length is 12.

      Flags: 1 octet of flags.  The flags are as defined in section 3.3
      of [I-D.ietf-isis-segment-routing-extensions] 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.





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

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

         SID/Label TLV (as defined in Section 2.1.1) used as 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]
   specifies the SRMS functionality along with SRMS preference of the
   node advertising the SRMS Prefix-to-SID Mapping ranges.

   This information is derived from the protocol specific
   advertisements.

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

   o  OSPFv2/OSPFv3, as defined by the SRMS Preference TLV in section
      3.4 of [I-D.ietf-ospf-segment-routing-extensions].  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.



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      Preference: 1 octet carrying an unsigned 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 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 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 of IS-IS (section 2.2.1 of
   [I-D.ietf-isis-segment-routing-extensions]), OSPFv2 (section 6.1 of
   [I-D.ietf-ospf-segment-routing-extensions]) and OSPFv3 (section 7.1
   of [I-D.ietf-ospf-ospfv3-segment-routing-extensions]).

   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




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

      Flags. 1 octet value which should be set as:

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

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

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

      Weight: 1 octet carrying the weight used for load-balancing
      purposes.  The use of weight is described in 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 2.2.1 of
         [I-D.ietf-isis-segment-routing-extensions].

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

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

   The Flags and, as an extension, the SID/Index/Label fields of this
   TLV are interpreted according to the respective underlying IS-IS,
   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 (or the equivalent OSPF Designated and Backup Designated
   Routers).  The LAN Adjacency Segment 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 NLRI would need to be originated for each
   additional adjacency in order to advertise the SR TLVs for these
   neighbor adjacencies.




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

   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                |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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


                  Figure 8: LAN Adjacency SID TLV Format

   Where:

      Type: 1100

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

      Flags. 1 octet value which should be set as:

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

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

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




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      Weight: 1 octet carrying the weight used for load-balancing
      purposes.  The use of weight is described in 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 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 2.2.2 of
         [I-D.ietf-isis-segment-routing-extensions].

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

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

   The Neighbor ID, Flags and, as an extension, the SID/Index/Label
   fields of this TLV are interpreted according to the respective
   underlying IS-IS, 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 TLV

   The L2 Bundle Member Attribute TLV identifies an L2 Bundle Member
   link which in turn is associated with a parent L3 link.  The L3 link
   is described by the Link NLRI defined in [RFC7752] and the L2 Bundle
   Member Attribute TLV is associated with the Link NLRI.  The TLV MAY
   include sub-TLVs which 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.  Multiple L2 Bundle Member Attribute TLVs MAY be
   associated with a Link NLRI.

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

   The L2 Bundle Member Attribute TLV has the following format:








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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Type            |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     L2 Bundle Member Descriptor               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Link attribute sub-TLVs(variable)          //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 9: L2 Bundle Member Attributes TLV Format

   Where:

      Type: 1172

      Length: Variable.

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

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


























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

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

2.3.  Prefix Attribute TLVs

   The following Prefix Attribute TLVs are defined:

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

                      Table 4: Prefix Attribute TLVs

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






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2.3.1.  Prefix SID TLV

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

   The 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 TLV Format

   Where:

      Type: 1158

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

      Flags: 1 octet value which should be set as:

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

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

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

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

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

      SID/Index/Label:



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

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

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

   The Flags and, as an extension, the SID/Index/Label fields of this
   TLV are interpreted according to the respective underlying IS-IS,
   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 2.1
   of [RFC7684], for OSPFv3 in section A.4.1.1 of [RFC5340] and for IS-
   IS in 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 field (according to the 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 2.1 of [RFC7794]




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

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

   The Flags field of this TLV is interpreted according to the
   respective underlying IS-IS, 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 TLV contains the IPv4 or IPv6 Router-ID of the
   originator of the Prefix.  For the IS-IS protocol this is derived
   from the IPv4/IPv6 Source Router ID sub-TLV as defined in section 2.2
   of [RFC7794].  For the OSPF protocol, this is derived from the Prefix
   Source Router-ID sub-TLV as defined in section 4 of
   [I-D.ietf-lsr-ospf-prefix-originator].

   The Source 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 Router-ID                    //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 12: Source Router-ID TLV Format

   Where:

      Type: 1171

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

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

2.3.4.  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)
   functionality [I-D.ietf-spring-segment-routing-ldp-interop], as
   defined in the respective underlying IGP SR extensions



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   [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).  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 been advertised with a Range TLV, is 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
   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: Range TLV Format

   Where:

      Type: 1159

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

      Flags: 1 octet value which should be set as:

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

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

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

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




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

   The Flags field of this TLV is interpreted according to the
   respective underlying IS-IS, 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

   OSPFv2/OSPFv3:
       OSPFv2/OSPFv3 Extended Prefix Range 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 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 the IS-IS Segment Routing Extensions TLVs and
   sub-TLVs mapped to the ones defined in this document.

   The following table, illustrates for each BGP-LS TLV, its equivalence
   in IS-IS.

















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   +------------+---------------+--------------------------------------+
   | Descriptio | IS-IS TLV     | Reference                            |
   | n          | /sub-TLV      |                                      |
   +------------+---------------+--------------------------------------+
   | SR Capabil | SR-           | [I-D.ietf-isis-segment-routing-exten |
   | ities      | Capabilities  | sions]                               |
   |            | sub-TLV (2)   |                                      |
   | SR         | SR-Algorithm  | [I-D.ietf-isis-segment-routing-exten |
   | Algorithm  | sub-TLV (19)  | sions]                               |
   | SR Local   | SR Local      | [I-D.ietf-isis-segment-routing-exten |
   | Block      | Block sub-TLV | sions]                               |
   |            | (22)          |                                      |
   | SRMS       | SRMS          | [I-D.ietf-isis-segment-routing-exten |
   | Preference | Preference    | sions]                               |
   |            | sub-TLV (19)  |                                      |
   | Adjacency  | Adj-SID sub-  | [I-D.ietf-isis-segment-routing-exten |
   | SID        | TLV (31)      | sions]                               |
   | LAN        | LAN-Adj-SID   | [I-D.ietf-isis-segment-routing-exten |
   | Adjacency  | sub-TLV (32)  | sions]                               |
   | SID        |               |                                      |
   | Prefix SID | Prefix-SID    | [I-D.ietf-isis-segment-routing-exten |
   |            | sub-TLV (3)   | sions]                               |
   | Range      | SID/Label     | [I-D.ietf-isis-segment-routing-exten |
   |            | Binding TLV   | sions]                               |
   |            | (149)         |                                      |
   | SID/Label  | SID/Label     | [I-D.ietf-isis-segment-routing-exten |
   |            | sub-TLV (1)   | sions]                               |
   | Prefix     | Prefix        | [RFC7794]                            |
   | Attribute  | Attributes    |                                      |
   | Flags      | Flags sub-TLV |                                      |
   |            | (4)           |                                      |
   | Source     | IPv4/IPv6     | [RFC7794]                            |
   | Router-ID  | Source Router |                                      |
   |            | ID sub-TLV    |                                      |
   |            | (11/12)       |                                      |
   | L2 Bundle  | L2 Bundle     | [I-D.ietf-isis-l2bundles]            |
   | Member     | Member        |                                      |
   | Attributes | 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 the OSPFv2 and OSPFv3 Segment Routing
   Extensions TLVs and sub-TLVs mapped to the ones defined in this
   document.



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   The following table, illustrates for each BGP-LS TLV, its equivalence
   in OSPFv2 and OSPFv3.

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

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





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

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




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3.  IANA Considerations

   Early allocation of codepoints has been done by IANA for this
   document from the registry "BGP-LS Node Descriptor, Link Descriptor,
   Prefix Descriptor, and Attribute TLVs" under the "BGP-LS Parameters"
   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                  | Section 2.3.1 |
     |      1159      | Range                       | Section 2.3.4 |
     |      1161      | SID/Label                   | Section 2.1.1 |
     |      1170      | Prefix Attribute Flags      | Section 2.3.2 |
     |      1171      | Source Router-ID            | Section 2.3.3 |
     |      1172      | L2 Bundle Member Attributes | Section 2.2.3 |
     +----------------+-----------------------------+---------------+

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

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. an application
   or a controller) and not the BGP protocol.



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   A consumer of the BGP-LS information retrieves this information over
   a BGP-LS session (refer Section 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 and any syntactic
   error in them would result in only that specific attribute being
   discarded with an error log.  The SR information introduced in BGP-LS
   by this specification, may be used by BGP-LS consumer applications
   like a SR 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 and to steer traffic on paths
   different from the underlying IGP based distributed 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
   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] and [I-D.ietf-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
   defined information ([I-D.ietf-isis-segment-routing-extensions],
   [I-D.ietf-ospf-segment-routing-extensions] and
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]).  These TLVs
   represent the SR information associated with the IGP node, link and
   prefix.  The IGP instances originating these TLVs are assumed to



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   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] and
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]) in order to
   prevent any security issue when propagating the TLVs into BGP-LS.

   BGP-LS SR extensions enable traffic engineering use-cases within the
   Segment Routing 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/
   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.

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





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7.  Acknowledgements

   The authors would like to thank Jeffrey Haas, Aijun Wang, Robert
   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 which helped correct issues and improve
   the document.

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 in progress), December 2018.

   [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>.






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   [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>.

   [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>.







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8.2.  Informative References

   [I-D.ietf-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 in progress), March 2019.

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

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

   [I-D.ietf-spring-sr-yang]
              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, DOI 10.17487/RFC5706, November 2009,
              <https://www.rfc-editor.org/info/rfc5706>.

Authors' Addresses

   Stefano Previdi
   Huawei Technologies
   Rome
   Italy

   Email: stefano@previdi.net


   Ketan Talaulikar (editor)
   Cisco Systems, Inc.
   India

   Email: ketant@cisco.com








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   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






























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