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
  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 Revised BSD License text as described in Section 4.e of the
  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: [email protected]


  Shunwan Zhuang
  Huawei
  Huawei Bld.
  No.156 Beiqing Rd.
  Beijing
  100095
  China
  Email: [email protected]


  Ketan Talaulikar (editor)
  Arrcus, Inc.
  India
  Email: [email protected]


  Sam Aldrin
  Google, Inc.
  Email: [email protected]


  Jeff Tantsura
  Microsoft
  Email: [email protected]


  Greg Mirsky
  Ericsson
  Email: [email protected]

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