Internet Engineering Task Force (IETF)                             Z. Li
Request for Comments: 9247                                     S. Zhuang
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                       K. Talaulikar, Ed.
                                                            Arrcus, Inc.
                                                               S. Aldrin
                                                            Google, Inc.
                                                             J. Tantsura
                                                               Microsoft
                                                               G. Mirsky
                                                                Ericsson
                                                               June 2022


    BGP - Link State (BGP-LS) Extensions for Seamless Bidirectional
                      Forwarding Detection (S-BFD)

Abstract

   Seamless Bidirectional Forwarding Detection (S-BFD) defines a
   simplified mechanism to use Bidirectional Forwarding Detection (BFD)
   with large portions of negotiation aspects eliminated, thus providing
   benefits such as quick provisioning as well as improved control and
   flexibility to network nodes initiating the path monitoring.  The
   link-state routing protocols (IS-IS and OSPF) have been extended to
   advertise the S-BFD Discriminators.

   This document defines extensions to the BGP - Link State (BGP-LS)
   address family to carry the S-BFD Discriminators' information via
   BGP.

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/rfc9247.

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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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
     2.1.  Requirements Language
   3.  BGP-LS Extensions for S-BFD Discriminators
   4.  IANA Considerations
   5.  Manageability Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Seamless Bidirectional Forwarding Detection (S-BFD) [RFC7880] defines
   a simplified mechanism to use Bidirectional Forwarding Detection
   (BFD) [RFC5880] with large portions of negotiation aspects
   eliminated, thus providing benefits such as quick provisioning as
   well as improved control and flexibility to network nodes initiating
   the path monitoring.

   For the monitoring of a service path end to end via S-BFD, the
   headend node (i.e., Initiator) needs to know the S-BFD Discriminator
   of the destination/tail-end node (i.e., Responder) of that service.
   The link-state routing protocols (IS-IS [RFC7883] and OSPF [RFC7884])
   have been extended to advertise the S-BFD Discriminators.  With this,
   an Initiator can learn the S-BFD Discriminator for all Responders
   within its IGP area/level or optionally within the domain.  With
   networks being divided into multiple IGP domains for scaling and
   operational considerations, the service endpoints that require end-
   to-end S-BFD monitoring often span across IGP domains.

   BGP - Link State (BGP-LS) [RFC7752] enables the collection and
   distribution of IGP link-state topology information via BGP sessions
   across IGP areas/levels and domains.  The S-BFD Discriminator(s) of a
   node can thus be distributed along with the topology information via
   BGP-LS across IGP domains and even across multiple Autonomous Systems
   (ASes) within an administrative domain.

   This document defines extensions to BGP-LS for carrying the S-BFD
   Discriminators' information.

2.  Terminology

   This memo makes use of the terms defined in [RFC7880].

2.1.  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.

3.  BGP-LS Extensions for S-BFD Discriminators

   BGP-LS [RFC7752] specifies the Node Network Layer Reachability
   Information (NLRI) for the advertisement of nodes and their
   attributes using the BGP-LS Attribute.  The S-BFD Discriminators of a
   node are considered a node-level attribute and are advertised as
   such.

   This document defines a new BGP-LS Attribute TLV called "S-BFD
   Discriminators TLV", and its format 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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Discriminator 1                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Discriminator 2 (Optional)                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               ...                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Discriminator n (Optional)                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: S-BFD Discriminators TLV

   where:

   Type:  1032

   Length:  variable.  It MUST be a minimum of 4 octets, and it
      increments by 4 octets for each additional discriminator.

   Discriminator n:  4 octets each, carrying an S-BFD local
      discriminator value of the node.  At least one discriminator MUST
      be included in the TLV.

   The S-BFD Discriminators TLV can be added to the BGP-LS Attribute
   associated with the Node NLRI that originates the corresponding
   underlying IGP TLV/sub-TLV as described below.  This information is
   derived from the protocol-specific advertisements as follows:

   *  IS-IS, as defined by the S-BFD Discriminators sub-TLV in
      [RFC7883].

   *  OSPFv2/OSPFv3, as defined by the S-BFD Discriminator TLV in
      [RFC7884].

4.  IANA Considerations

   IANA has permanently allocated the following code point in the "BGP-
   LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
   TLVs" registry.  The column "IS-IS TLV/Sub-TLV" defined in the
   registry does not require any value and should be left empty.

         +================+======================+===============+
         | TLV Code Point | Description          | Reference     |
         +================+======================+===============+
         | 1032           | S-BFD Discriminators | This document |
         +----------------+----------------------+---------------+

          Table 1: S-BFD Discriminators TLV Code Point Allocation

5.  Manageability Considerations

   The new protocol extensions introduced in this document augment the
   existing IGP topology information that was distributed via BGP-LS
   [RFC7752].  Procedures and protocol extensions defined in this
   document do not affect BGP protocol operations and management other
   than as discussed in "Manageability Considerations" (Section 6) of
   [RFC7752].  Specifically, the malformed NLRIs attribute tests in
   "Fault Management" (Section 6.2.2) of [RFC7752] now encompass the new
   TLV for the BGP-LS NLRI in this document.

6.  Security Considerations

   The new protocol extensions introduced in this document augment the
   existing IGP topology information that can be distributed via BGP-LS
   [RFC7752].  Procedures and protocol extensions defined in this
   document do not affect the BGP security model other than as discussed
   in "Security Considerations" (Section 8) of [RFC7752], i.e., the
   aspects related to limiting the nodes and consumers with which the
   topology information is shared via BGP-LS to trusted entities within
   an administrative domain.

   The TLV introduced in this document is used to propagate IGP-defined
   information (see [RFC7883] and [RFC7884]).  The TLV represents
   information used to set up S-BFD sessions.  The IGP instances
   originating this information are assumed to support any required
   security and authentication mechanisms (as described in [RFC7883] and
   [RFC7884]).

   Advertising the S-BFD Discriminators via BGP-LS makes it possible for
   attackers to initiate S-BFD sessions using the advertised
   information.  The vulnerabilities this poses and how to mitigate them
   are discussed in [RFC7880].

7.  References

7.1.  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>.

   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
              <https://www.rfc-editor.org/info/rfc7880>.

   [RFC7883]  Ginsberg, L., Akiya, N., and M. Chen, "Advertising
              Seamless Bidirectional Forwarding Detection (S-BFD)
              Discriminators in IS-IS", RFC 7883, DOI 10.17487/RFC7883,
              July 2016, <https://www.rfc-editor.org/info/rfc7883>.

   [RFC7884]  Pignataro, C., Bhatia, M., Aldrin, S., and T. Ranganath,
              "OSPF Extensions to Advertise Seamless Bidirectional
              Forwarding Detection (S-BFD) Target Discriminators",
              RFC 7884, DOI 10.17487/RFC7884, July 2016,
              <https://www.rfc-editor.org/info/rfc7884>.

   [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>.

7.2.  Informative References

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

Acknowledgements

   The authors would like to thank Nan Wu for his contributions to this
   work.  The authors would also like to thank Gunter Van de Velde and
   Thomas Fossati for their reviews as well as Jeff Haas for his
   shepherd review and Alvaro Retana for his AD review of this document.

Authors' Addresses

   Zhenbin Li
   Huawei
   Huawei Bld.
   No.156 Beiqing Rd.
   Beijing
   100095
   China
   Email: lizhenbin@huawei.com


   Shunwan Zhuang
   Huawei
   Huawei Bld.
   No.156 Beiqing Rd.
   Beijing
   100095
   China
   Email: zhuangshunwan@huawei.com


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


   Sam Aldrin
   Google, Inc.
   Email: aldrin.ietf@gmail.com


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


   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com