



Internet Engineering Task Force (IETF)                K. Talaulikar, Ed.
Request for Comments: 9294                                   Arrcus Inc.
Category: Standards Track                                      P. Psenak
ISSN: 2070-1721                                            Cisco Systems
                                                             J. Tantsura
                                                               Microsoft
                                                             August 2022


  Application-Specific Link Attributes Advertisement Using the Border
                 Gateway Protocol - Link State (BGP-LS)

Abstract

   Extensions have been defined for link-state routing protocols that
   enable distribution of application-specific link attributes for
   existing as well as newer applications such as Segment Routing (SR).
   This document defines extensions to the Border Gateway Protocol -
   Link State (BGP-LS) to enable the advertisement of these application-
   specific attributes as a part of the topology information from the
   network.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9294.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   to this document.  Code Components extracted from this document must
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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Requirements Language
   2.  Application-Specific Link Attributes TLV
   3.  Application-Specific Link Attributes
   4.  Procedures
     4.1.  Illustration for IS-IS
   5.  Deployment Considerations
   6.  IANA Considerations
   7.  Manageability Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   The Border Gateway Protocol - Link State (BGP-LS) [RFC7752] enables
   the distribution of the link-state topology information from link-
   state routing protocols (viz., IS-IS [RFC1195], OSPFv2 [RFC2328], and
   OSPFv3 [RFC5340]) to an application like a controller or Path
   Computation Engine (PCE) via BGP.  The controller or PCE gets the
   end-to-end topology information across IGP domains so it can perform
   path computations for use cases like end-to-end traffic engineering
   (TE).

   The link-state topology information distributed via BGP-LS includes
   link attributes that were originally defined for MPLS TE (i.e., using
   RSVP-TE [RFC3209] or GMPLS [RFC4202] applications).  In recent years,
   applications, such as Segment Routing (SR) Policy [RFC8402] and Loop-
   Free Alternates (LFA) [RFC5286], which also make use of link
   attributes, have been introduced.  [RFC8919] and [RFC8920] define
   extensions for IS-IS and OSPF, respectively, that enable advertising
   application-specific link attributes for these and other future
   applications.  This has resulted in the need for a similar BGP-LS
   extension to include this additional link-state topology information
   from the link-state routing protocols.

   This document defines the BGP-LS extensions for the advertisement of
   application-specific link attributes.  It describes the advertisement
   of these link attributes as top-level TLVs (i.e., as TLVs of the BGP-
   LS Attribute) and as sub-TLVs of the (top-level) Application-Specific
   Link Attributes (ASLA) TLV.  The document also describes the
   procedures for the advertisement of these attributes from the
   underlying IGPs and discusses their deployment aspects.

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.  Application-Specific Link Attributes TLV

   BGP-LS [RFC7752] specifies the Link Network Layer Reachability
   Information (NLRI) for the advertisement of links and their
   attributes using the BGP-LS Attribute.  The ASLA TLV is an optional
   top-level BGP-LS Attribute TLV that is introduced for Link NLRIs.  It
   is defined such that it may act as a container for certain existing
   and future link attributes that require application-specific
   definition.

   The format of this TLV is as follows and is similar to the
   corresponding ASLA sub-TLVs defined for OSPF and IS-IS in [RFC8920]
   and [RFC8919], respectively.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SABM Length   | UDABM Length  |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Standard Application Identifier Bit Mask (variable)      //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    User-Defined Application Identifier Bit Mask (variable)   //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Link Attribute sub-TLVs                 //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 1: Application-Specific Link Attributes TLV

   where:

   Type:  1122

   Length:  variable

   SABM Length:  1-octet field that carries the Standard Application
      Identifier Bit Mask Length in octets as defined in [RFC8920].

   UDABM Length:  1-octet field that carries the User-Defined
      Application Identifier Bit Mask Length in octets as defined in
      [RFC8920].

   Reserved:  2-octet field that MUST be set to zero on transmission and
      MUST be ignored on reception.

   Standard Application Identifier Bit Mask:  An optional set of bits
      (of size 0, 4, or 8 octets as indicated by the SABM Length), where
      each bit represents a single standard application as defined in
      [RFC8919].

   User-Defined Application Identifier Bit Mask:  An optional set of
      bits (of size 0, 4, or 8 octets as indicated by the UDABM Length),
      where each bit represents a single user-defined application as
      defined in [RFC8919] and [RFC8920].

   Link Attribute sub-TLVs:  BGP-LS Attribute TLVs corresponding to the
      Link NLRI that are application-specific (including existing ones
      as specified in Section 3) are included as sub-TLVs of the ASLA
      TLV.

   The semantics associated with the standard and user-defined bit masks
   as well as the encoding scheme for application-specific attributes
   are as specified in [RFC8920].

   The ASLA TLV and its sub-TLVs can only be added to the BGP-LS
   Attribute associated with the Link NLRI of the node that originates
   the underlying IGP link attribute TLVs and sub-TLVs.  The procedures
   for originating link attributes in the ASLA TLV from underlying IGPs
   are specified in Section 4.

3.  Application-Specific Link Attributes

   Several BGP-LS Attribute TLVs corresponding to the Link NLRI are
   defined in BGP-LS [RFC7752], and more may be added in the future.
   Those attributes that have been determined to be, and advertised as,
   application-specific in the underlying IGPs are also encoded
   similarly in BGP-LS.

   The following table lists the currently defined BGP-LS Attribute TLVs
   corresponding to Link NLRI that can have application-specific
   semantics based on the underlying IGP specifications [RFC8919]
   [RFC8920].  These were originally defined with semantics for RSVP-TE
   and GMPLS applications in BGP-LS by the respective reference
   documents.

     +================+========================+====================+
     | TLV Code Point | Description            | Reference Document |
     +================+========================+====================+
     |      1088      | Administrative group   | [RFC7752]          |
     |                | (color)                |                    |
     +----------------+------------------------+--------------------+
     |      1092      | TE Default Metric      | [RFC7752]          |
     +----------------+------------------------+--------------------+
     |      1096      | Shared Risk Link Group | [RFC7752]          |
     +----------------+------------------------+--------------------+
     |      1114      | Unidirectional Link    | [RFC8571]          |
     |                | Delay                  |                    |
     +----------------+------------------------+--------------------+
     |      1115      | Min/Max Unidirectional | [RFC8571]          |
     |                | Link Delay             |                    |
     +----------------+------------------------+--------------------+
     |      1116      | Unidirectional Delay   | [RFC8571]          |
     |                | Variation              |                    |
     +----------------+------------------------+--------------------+
     |      1117      | Unidirectional Link    | [RFC8571]          |
     |                | Loss                   |                    |
     +----------------+------------------------+--------------------+
     |      1118      | Unidirectional         | [RFC8571]          |
     |                | Residual Bandwidth     |                    |
     +----------------+------------------------+--------------------+
     |      1119      | Unidirectional         | [RFC8571]          |
     |                | Available Bandwidth    |                    |
     +----------------+------------------------+--------------------+
     |      1120      | Unidirectional         | [RFC8571]          |
     |                | Utilized Bandwidth     |                    |
     +----------------+------------------------+--------------------+
     |      1173      | Extended               | [RFC9104]          |
     |                | Administrative Group   |                    |
     +----------------+------------------------+--------------------+

     Table 1: Existing BGP-LS TLVs Identified as Application-Specific

   All the BGP-LS Attribute TLVs listed in the table above are REQUIRED
   to be advertised as a top-level TLV in the BGP-LS Attribute when used
   to carry link attributes specific to RSVP-TE.

   BGP-LS Attribute TLVs corresponding to Link NLRI that are advertised
   in the underlying IGP as application-specific are REQUIRED to be
   encoded within an ASLA TLV.

   Link attributes that do not have application-specific semantics MUST
   NOT be advertised within the ASLA TLV.

   When the same application-specific link attributes are advertised
   both within the ASLA TLV and as top-level TLVs in the BGP-LS
   Attribute, the attributes advertised within the ASLA TLV take
   precedence for the applications indicated in the ASLA TLV encoding.

4.  Procedures

   The BGP-LS originator learns of the association of an application-
   specific attribute to one or more applications from the underlying
   IGP protocol Link State Advertisements (LSAs) or Link State Packets
   (LSPs) from which it is advertising the topology information.
   [RFC8920] and [RFC8919] specify the mechanisms for advertising
   application-specific link attributes in OSPF and IS-IS, respectively.

   Application-specific link attributes received from an IGP node
   without the use of ASLA encodings continue to be encoded using the
   respective BGP-LS top-level TLVs listed in Table 1 as specified in
   their respective reference documents.

   While the ASLA encoding in OSPF is similar to that of BGP-LS, the
   encoding in IS-IS differs and requires additional procedures when
   conveying information into BGP-LS.  One of these differences arises
   from the presence of the L-flag in the IS-IS encoding.  Another
   difference arises due to the requirement to collate information from
   two types of IS-IS encodings for application-specific link
   information (i.e., the IS-IS ASLA sub-TLV and the IS-IS Application-
   Specific Shared Risk Link Group (SRLG) TLV) [RFC8919] and to carry
   them together in the BGP-LS ASLA TLV.

   A BGP-LS originator node that is advertising link-state information
   from the underlying IGP using ASLA encodings determines their BGP-LS
   encoding based on the following rules:

   1.  Application-specific link attributes received from an OSPF node
       using an ASLA sub-TLV or from an IS-IS node using either an ASLA
       sub-TLV or an Application-Specific SRLG TLV MUST be encoded in
       the BGP-LS ASLA TLV as sub-TLVs.  Exceptions to this rule are
       specified in (2)(F) and (2)(G) below.

   2.  In the case of IS-IS, the specific procedures below are to be
       followed:

       A.  When application-specific link attributes are received from a
           node with the L-flag set in the IS-IS ASLA sub-TLV and when
           application bits (other than RSVP-TE) are set in the
           application bit masks, then the application-specific link
           attributes advertised in the corresponding legacy IS-IS TLVs
           and sub-TLVs MUST be encoded within the BGP-LS ASLA TLV as
           sub-TLVs with the application bits (other than the RSVP-TE
           bit) copied from the IS-IS ASLA sub-TLV.  The link attributes
           advertised in the legacy IS-IS TLVs and sub-TLVs are also
           advertised in BGP-LS top-level TLVs as per [RFC7752],
           [RFC8571], and [RFC9104].  The same procedure also applies
           for the advertisement of the SRLG values from the IS-IS
           Application-Specific SRLG TLV.

       B.  When the IS-IS ASLA sub-TLV has the RSVP-TE application bit
           set, then the link attributes for the corresponding IS-IS
           ASLA sub-TLVs MUST be encoded using the respective BGP-LS
           top-level TLVs as per [RFC7752], [RFC8571], and [RFC9104].
           Similarly, when the IS-IS Application-Specific SRLG TLV has
           the RSVP-TE application bit set, then the SRLG values within
           it MUST be encoded using the top-level BGP-LS SRLG TLV (1096)
           as per [RFC7752].

       C.  The SRLGs advertised in one or more IS-IS Application-
           Specific SRLG TLVs and the other link attributes advertised
           in one or more IS-IS ASLA sub-TLVs are REQUIRED to be
           collated, on a per-application basis, only for those
           applications that meet all the following criteria:

           *  their bit is set in the SABM or UDABM in one of the two
              types of IS-IS encodings (e.g., IS-IS ASLA sub-TLV)

           *  the other encoding type (e.g., IS-IS Application Specific
              SRLG TLV) has an advertisement with zero-length
              application bit masks

           *  there is no corresponding advertisement of that other
              encoding type (following the example, IS-IS Application
              Specific SRLG TLV) with that specific application bit set

           For each such application, its collated information MUST be
           carried in a BGP-LS ASLA TLV with that application's bit set
           in the SABM or UDABM.  See the illustration in Section 4.1.

       D.  If the resulting set of collated link attributes and SRLG
           values is common across multiple applications, they MAY be
           advertised in a common BGP-LS ASLA TLV instance where the
           bits for all such applications would be set in the
           application bit mask.

       E.  Both the SRLG values from IS-IS Application-Specific SRLG
           TLVs and the link attributes from IS-IS ASLA sub-TLVs, with
           the zero-length application bit mask, MUST be advertised into
           a BGP-LS ASLA TLV with a zero-length application bit mask,
           independent of the collation described above.

       F.  [RFC8919] allows the advertisement of the Maximum Link
           Bandwidth within an IS-IS ASLA sub-TLV even though it is not
           an application-specific attribute.  However, when originating
           the Maximum Link Bandwidth into BGP-LS, the attribute MUST be
           encoded only in the top-level BGP-LS Maximum Link Bandwidth
           TLV (1089) and MUST NOT be advertised within the BGP-LS ASLA
           TLV.

       G.  [RFC8919] also allows the advertisement of the Maximum
           Reservable Link Bandwidth and the Unreserved Bandwidth within
           an IS-IS ASLA sub-TLV even though these attributes are
           specific to RSVP-TE application.  However, when originating
           the Maximum Reservable Link Bandwidth and Unreserved
           Bandwidth into BGP-LS, these attributes MUST be encoded only
           in the BGP-LS top-level Maximum Reservable Link Bandwidth TLV
           (1090) and Unreserved Bandwidth TLV (1091), respectively, and
           not within the BGP-LS ASLA TLV.

   These rules ensure that a BGP-LS originator performs the
   advertisement for all application-specific link attributes from the
   IGP nodes that support the ASLA extension.  Furthermore, it also
   ensures that the top-level BGP-LS TLVs defined for RSVP-TE and GMPLS
   applications continue to be used for advertisement of their
   application-specific attributes.

   A BGP-LS speaker would normally advertise all the application-
   specific link attributes corresponding to RSVP-TE and GMPLS
   applications as existing top-level BGP-LS TLVs while for other
   applications they are encoded in the ASLA TLV(s) with appropriate
   applicable bit mask setting.  An application-specific attribute value
   received via a sub-TLV within the ASLA TLV has precedence over the
   value received via a top-level TLV.

4.1.  Illustration for IS-IS

   This section illustrates the procedure for the advertisement of
   application-specific link attributes from IS-IS into BGP-LS.

   Consider the following advertisements for a link in IS-IS.  We start
   with this set:

   a.  IS-IS ASLA sub-TLV with the S, F, and X bits set on it that
       carries certain application-specific link attributes

   b.  IS-IS Application-Specific SRLG TLV with zero-length bit masks
       with a set of application-specific SRLGs

   c.  IS-IS Application-Specific SRLG TLV with the X bit set on it with
       a set of application-specific SRLGs

   The corresponding BGP-LS advertisements for that link are determined
   as follows:

   First, based on rule (1), the advertisements are conveyed to BGP-LS
   to get the following "updated set":

   1.  ASLA with the S, F, and X bits set on it that carries link
       attributes from IS-IS advertisement (a)

   2.  ASLA SRLG with zero-length bit masks with a set of SRLGs from IS-
       IS advertisement (b)

   3.  ASLA SRLG with the X bit set on it with a set of SRLGs from IS-IS
       advertisement (c)

   Next, we apply the rules from (2) to this "updated set", because all
   of them were sourced from IS-IS, to derive a new set.

   The next rule that applies is (2)(c), and it is determined that
   collation is required for applications S and F; therefore, we get the
   following "final set":

   1.  ASLA with the S bit set on it that carries link attributes from
       IS-IS advertisement (a) and SRLGs from IS-IS advertisement (b)
       (this is collation for application S based on (2)(c))

   2.  ASLA with the F bit set on it that carries link attributes from
       IS-IS advertisement (a) and SRLGs from IS-IS advertisement (b)
       (this is collation for application F based on (2)(c))

   3.  ASLA with the X bit set on it that carries link attributes from
       IS-IS advertisement (a) (remaining application not affected by
       collation based on (2)(c))

   4.  ASLA with zero-length bit masks with SRLGs from IS-IS
       advertisement (b) (not affected by (2)(c) and therefore carried
       forward unchanged from the "updated set")

   5.  ASLA with the X bit set on it with SRLGs from IS-IS advertisement
       (c) (not affected by (2)(c) and therefore carried forward
       unchanged from the "updated set")

   Implementations may optionally perform further consolidation by
   processing the "final set" above based on (2)(d) to determine the
   following "consolidated final set":

   1.  ASLA with the S and F bits set on it that carries application-
       specific link attributes from IS-IS advertisement (a) and SRLGs
       from IS-IS advertisement (b) (this is the consolidation of items
       1 and 2 of the "final set" based on (2)(d))

   2.  ASLA with the X bit set on it that carries certain application-
       specific link attributes from IS-IS advertisement (a) (it is
       unaffected by this consolidation)

   3.  ASLA with zero-length bit masks with a set of application-
       specific SRLGs from IS-IS advertisement (b) (this is retained
       based on (2)(e) and is unaffected by any further consolidation)

   4.  ASLA with the X bit set on it with a set of application-specific
       SRLGs from IS-IS advertisement (c) (it is unaffected by this
       consolidation)

   Further optimization (e.g., combining (2) and (4) from the
   "consolidated final set" above into a single BGP-LS ASLA TLV) may be
   possible while ensuring that the semantics are preserved between the
   IS-IS and BGP-LS advertisements.  Such optimizations are outside the
   scope of this document.

5.  Deployment Considerations

   BGP-LS sources the link-state topology information (including the
   extensions introduced by this document) from the underlying link-
   state IGP protocols.  The various deployment aspects related to the
   advertisement and use of application-specific link attributes are
   discussed in the Deployment Considerations sections of [RFC8920] and
   [RFC8919].  The IGP backward-compatibility aspects described in those
   documents associated with application-specific link attributes along
   with the BGP-LS procedures specified in this document enable backward
   compatibility in deployments of existing implementations of
   [RFC7752], [RFC8571], and [RFC9104] for applications such as RSVP-TE,
   SR Policy, and LFA.

   It is recommended that only nodes supporting this specification are
   selected as originators of BGP-LS information when advertising the
   link-state information from the IGPs in deployments supporting
   application-specific link attributes.

   BGP-LS consumers that do not support this specification can continue
   to use the existing top-level TLVs for link attributes for existing
   applications as discussed above.  However, they would be able to
   support neither the application-specific link attributes nor newer
   applications that may be encoded only using the ASLA TLV.

6.  IANA Considerations

   IANA has assigned a code point from the "BGP-LS Node Descriptor, Link
   Descriptor, Prefix Descriptor, and Attribute TLVs" registry as
   described in the following table.  There is no "IS-IS TLV/Sub-TLV"
   value for this entry.

   +================+======================================+===========+
   | TLV Code Point | Description                          | Reference |
   +================+======================================+===========+
   | 1122           | Application-Specific                 | RFC 9294  |
   |                | Link Attributes                      |           |
   +----------------+--------------------------------------+-----------+

                  Table 2: ASLA TLV Code Point Allocation

7.  Manageability Considerations

   The protocol extensions introduced in this document augment the
   existing IGP topology information defined in [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 NLRI attribute tests in the Fault Management section of
   [RFC7752] now encompass the BGP-LS TLVs defined in this document.

   The extensions specified in this document do not specify any new
   configuration or monitoring aspects in BGP or BGP-LS.  The
   specification of BGP models is an ongoing work based on
   [IDR-BGP-MODEL].

8.  Security Considerations

   Security considerations for acquiring and distributing BGP-LS
   information are discussed in [RFC7752].  Specifically, the
   considerations related to topology information, which are related to
   traffic engineering, apply.

   The TLVs introduced in this document are used to propagate the
   application-specific link attributes IGP extensions defined in
   [RFC8919] and [RFC8920].  It is assumed that the IGP instances
   originating these TLVs will support all the required security (as
   described in [RFC8919] and [RFC8920]).

   This document defines a new way to advertise link attributes.
   Tampering with the information defined in this document may affect
   applications using it, including impacting traffic engineering, which
   uses various link attributes for its path computation.  As the
   advertisements defined in this document limit the scope to specific
   applications, the impact of tampering is similarly limited in scope.
   The advertisement of the link attribute information defined in this
   document presents no significant additional risk beyond that
   associated with the existing link attribute information already
   supported in [RFC7752].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [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>.

   [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>.

   [RFC8919]  Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              RFC 8919, DOI 10.17487/RFC8919, October 2020,
              <https://www.rfc-editor.org/info/rfc8919>.

   [RFC8920]  Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
              J., and J. Drake, "OSPF Application-Specific Link
              Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020,
              <https://www.rfc-editor.org/info/rfc8920>.

   [RFC9104]  Tantsura, J., Wang, Z., Wu, Q., and K. Talaulikar,
              "Distribution of Traffic Engineering Extended
              Administrative Groups Using the Border Gateway Protocol -
              Link State (BGP-LS)", RFC 9104, DOI 10.17487/RFC9104,
              August 2021, <https://www.rfc-editor.org/info/rfc9104>.

9.2.  Informative References

   [IDR-BGP-MODEL]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-14, 3
              July 2022, <https://datatracker.ietf.org/doc/html/draft-
              ietf-idr-bgp-model-14>.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://www.rfc-editor.org/info/rfc1195>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [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>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [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>.

   [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>.

Acknowledgements

   The authors would like to thank Les Ginsberg, Baalajee S., Amalesh
   Maity, Acee Lindem, Keyur Patel, Paul Wouters, Rudy Selderslaghs,
   Kristy Paine, and Shraddha Hegde for their review and feedback on
   this document.  The authors would like to thank Alvaro Retana for his
   very detailed AD review and comments that improved this document.
   The authors would also like to thank John Scudder for his detailed
   review and feedback on clarifying the procedures along with the
   example in Section 4.

Authors' Addresses

   Ketan Talaulikar (editor)
   Arrcus Inc.
   India
   Email: ketant.ietf@gmail.com


   Peter Psenak
   Cisco Systems
   Slovakia
   Email: ppsenak@cisco.com


   Jeff Tantsura
   Microsoft
   Email: jefftant.ietf@gmail.com
