\
Inter-Domain Routing                                  K. Talaulikar, Ed.
Internet-Draft                                                Arrcus Inc
Intended status: Standards Track                               P. Psenak
Expires: October 30, 2022                                  Cisco Systems
                                                             J. Tantsura
                                                               Microsoft
                                                          April 28, 2022


   Application-Specific Attributes Advertisement with BGP Link-State
               draft-ietf-idr-bgp-ls-app-specific-attr-10

Abstract

   Various link attributes have been defined in link-state routing
   protocols like OSPF and IS-IS in the context of the MPLS Traffic
   Engineering (TE) and GMPLS.  BGP Link-State (BGP-LS) extensions have
   been defined to distribute these attributes along with other topology
   information from these link-state routing protocols.

   New 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.  This
   document defines extensions to 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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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

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

   This Internet-Draft will expire on October 30, 2022.








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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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Application Specific Link Attributes TLV  . . . . . . . . . .   3
   3.  Application-Specific Link Attributes  . . . . . . . . . . . .   5
   4.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Deployment Considerations . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   BGP Link-State [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/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 traditional MPLS
   Traffic Engineering (i.e., using RSVP-TE [RFC3209]) or GMPLS
   [RFC4202]) applications.  In recent years new applications, such as
   Segment Routing (SR) Policy [RFC8402] and Loop-Free Alternates (LFA)
   [RFC5286], that also make use of link attributes have been



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   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 new (top-level) Application
   Specific Link Attributes 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

   The BGP-LS [RFC7752] specifies the Link NLRI for the advertisement of
   links and their attributes using the BGP-LS Attribute.  The
   Application-Specific Link Attributes (ASLA) TLV is a new 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.















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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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | 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:

   o  Type: 1122

   o  Length: variable.

   o  SABM Length : Standard Application Identifier Bit Mask Length in
      octets as defined in [RFC8920].

   o  UDABM Length : User-Defined Application Identifier Bit Mask Length
      in octets as defined in [RFC8920].

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

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

   o  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].





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   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/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 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 in a
   similar manner in BGP-LS.

   The following table lists the currently defined BGP-LS Attributes
   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   | Description                   | Reference         |
   |     Point     |                               | Document          |
   +---------------+-------------------------------+-------------------+
   |      1088     | Administrative group (color)  | [RFC7752]         |
   |      1092     | TE Default Metric             | [RFC7752]         |
   |      1096     | Shared Risk Link Group        | [RFC7752]         |
   |      1114     | Unidirectional Link Delay     | [RFC8571]         |
   |      1115     | Min/Max Unidirectional Link   | [RFC8571]         |
   |               | Delay                         |                   |
   |      1116     | Unidirectional Delay          | [RFC8571]         |
   |               | Variation                     |                   |
   |      1117     | Unidirectional Link Loss      | [RFC8571]         |
   |      1118     | Unidirectional Residual       | [RFC8571]         |
   |               | Bandwidth                     |                   |
   |      1119     | Unidirectional Available      | [RFC8571]         |
   |               | Bandwidth                     |                   |
   |      1120     | Unidirectional Utilized       | [RFC8571]         |
   |               | Bandwidth                     |                   |
   |      1173     | Extended Administrative Group | [RFC9104]         |
   +---------------+-------------------------------+-------------------+

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

   All the BGP-LS Attribute TLVs defined in the table above are REQUIRED
   to be advertised as a top-level TLV in the BGP-LS Attribute for
   carrying link attributes specific to RSVP-TE.



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   BGP-LS Attribute TLVs corresponding to Link NLRI that are identified
   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 LSA/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.

   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 ASLA sub-TLV or from an IS-IS node using either ASLA sub-
       TLV or ASLA 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 following specific procedures are to be
       followed:

       A.  When application-specific link attributes are received from a
           node with the L bit set in the ASLA sub-TLV and 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/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/sub-TLVs are also advertised in BGP-LS top-level TLVs as



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           per [RFC7752] [RFC8571] [RFC9104].  The same procedure also
           applies for the advertisement of the SRLG values from the IS-
           IS ASLA SRLG TLV.

       B.  When the ASLA sub-TLV has the RSVP-TE application bit set,
           then the link attributes for the corresponding ASLA sub-TLV
           MUST be encoded using the respective BGP-LS top-level TLVs as
           per [RFC7752] [RFC8571] [RFC9104].  Similarly, when the ASLA
           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 IS-IS SRLG ASLA TLVs and the other
           link attributes advertised in IS-IS ASLA sub-TLVs are
           REQUIRED to be collated, on a per-application basis, for all
           applications that have their bit set in the SABM/UDABM in at
           least one of the aforementioned TLV types.  When performing
           this collation, only the TLVs with the application's bit set
           in SABM/UDABM MUST be used when such TLVs are available from
           either TLV types.  If the bit for an application is set in
           the SABM/UDABM of only one of the TLV types, then the
           attributes from the other TLV type with zero-length
           application bit mask MUST be also collated for that
           application, if such TLV is available.  Such collated link
           attributes are advertised in a per-application instance of
           the BGP-LS ASLA TLV.

       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 ASLA 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 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.





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       G.  [RFC8919] also allows the advertisement of the Maximum
           Reservable Link Bandwidth and the Unreserved Bandwidth within
           an 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 or do not 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 ASLA TLV(s) with appropriate
   applicable bit mask setting.  The application-specific attribute
   value received via sub-TLVs within the ASLA TLV have preference over
   the value received via the top-level TLVs.

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] [RFC9104] for applications such as RSVP-TE, SR Policy, and
   LFA.

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

   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.  They would, however, not be able to
   support neither the application-specific link attributes nor newer
   applications that may be encoded only using the ASLA TLV.



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6.  IANA Considerations

   IANA has assigned, through the early allocation process, the
   following code-point from the "BGP-LS Node Descriptor, Link
   Descriptor, Prefix Descriptor, and Attribute TLVs" registry.  This
   document requests that the allocation be made permanent.  The column
   "IS-IS TLV/Sub-TLV" defined in the registry does not require any
   value and should be left empty.

   +------------+------------------------------------------+----------+
   | Code Point |         Description                      | Length   |
   +------------+------------------------------------------+----------+
   |   1122     | Application-Specific Link Attributes TLV | variable |
   +------------+------------------------------------------+----------+

               Table 2: ASLA TLV Code-Point Allocation


7.  Manageability Considerations

   The new 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 NLRIs attribute tests in the Fault Management section of
   [RFC7752] now encompasses 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
   [I-D.ietf-idr-bgp-model].

8.  Security Considerations

   Security considerations for acquiring and distributing BGP-LS
   information are discussed in [RFC7752].

   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]) to prevent any security issues
   when propagating the TLVs into BGP-LS.

   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



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   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.  Acknowledgements

   The authors would like to thank Les Ginsberg, Baalajee S, Amalesh
   Maity, Acee Lindem, Keyur Patel, Paul Wouters, and Rudy Selderslaghs
   for their review and feedback on this document.  The authors would
   also like to thank Alvaro Retana for his very detailed AD review and
   comments for improving this document.

10.  References

10.1.  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>.






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   [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>.

10.2.  Informative References

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", draft-ietf-idr-
              bgp-model-13 (work in progress), March 2022.

   [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>.







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   [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>.

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


























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