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Advertising Seamless Bidirectional Forwarding Detection (S-BFD) Discriminators in IS-IS
RFC 7883

Document Type RFC - Proposed Standard (July 2016)
Authors Les Ginsberg , Nobo Akiya , Mach Chen
Last updated 2016-07-12
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
IESG Responsible AD Alia Atlas
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RFC 7883
Internet Engineering Task Force (IETF)                       L. Ginsberg
Request for Comments: 7883                                 Cisco Systems
Category: Standards Track                                       N. Akiya
ISSN: 2070-1721                                      Big Switch Networks
                                                                 M. Chen
                                                               July 2016

    Advertising Seamless Bidirectional Forwarding Detection (S-BFD)
                        Discriminators in IS-IS


   This document defines a means of advertising one or more Seamless
   Bidirectional Forwarding Detection (S-BFD) Discriminators using the

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

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RFC 7883        Advertising S-BFD Discriminators in IS-IS      July 2016

Copyright Notice

   Copyright (c) 2016 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
   ( 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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................3
   2. Encoding Format .................................................3
   3. IANA Considerations .............................................4
   4. Security Considerations .........................................4
   5. Normative References ............................................4
   Acknowledgements ...................................................5
   Authors' Addresses .................................................5

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RFC 7883        Advertising S-BFD Discriminators in IS-IS      July 2016

1.  Introduction

   [RFC7880] defines a simplified mechanism for using Bidirectional
   Forwarding Detection (BFD) [RFC5880].  This mechanism depends on
   network nodes knowing the BFD Discriminators that each node in the
   network has reserved for this purpose.  The use of the Intermediate
   System to Intermediate System (IS-IS) [IS-IS] protocol is one
   possible means of advertising these discriminators.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Encoding Format

   The IS-IS Router CAPABILITY TLV as defined in [RFC4971] will be used
   to advertise Seamless BFD (S-BFD) Discriminators.  A new sub-TLV is
   defined as described below.  S-BFD Discriminators sub-TLVs are
   formatted as specified in [RFC5305].

                                                  No. of octets
                 | Type (20)                   |     1
                 | Length (multiple of 4)      |     1
                 | Discriminator Value(s)      |     4/Discriminator
                 :                             :

   The inclusion of an S-BFD Discriminators sub-TLV in a Router
   CAPABILITY TLV is optional.  Multiple S-BFD Discriminators sub-TLVs
   MAY be advertised by an IS.  How a given discriminator is mapped to a
   specific use case when multiple S-BFD Discriminators are advertised
   is out of scope for this document.

   S-BFD Discriminator advertisements MAY be flooded within an area or
   throughout the domain, using the procedures specified in [RFC4971].
   The appropriate flooding scope depends on the intended use of S-BFD.
   If S-BFD usage will be exclusively within a Level-1 area, then area
   scope is appropriate.  If S-BFD usage will span different Level-1
   areas, then domain scope is appropriate.

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RFC 7883        Advertising S-BFD Discriminators in IS-IS      July 2016

3.  IANA Considerations

   IANA has added a new sub-TLV in the "Sub-TLVs for TLV 242" registry.
   The registration is as follows:

      Value  Description
      -----  --------------------
      20     S-BFD Discriminators

4.  Security Considerations

   Security concerns for IS-IS are addressed in [IS-IS], [RFC5304], and
   [RFC5310].  The new S-BFD Discriminators sub-TLV does not introduce
   any new security risks for IS-IS.

   Advertising the S-BFD Discriminators 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

5.  Normative References

   [IS-IS]    International Organization for Standardization,
              "Intermediate System to Intermediate System intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode network service (ISO 8473)",
              ISO Standard 10589, 2002.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4971]  Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
              "Intermediate System to Intermediate System (IS-IS)
              Extensions for Advertising Router Information", RFC 4971,
              DOI 10.17487/RFC4971, July 2007,

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304,
              October 2008, <>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305,
              October 2008, <>.

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RFC 7883        Advertising S-BFD Discriminators in IS-IS      July 2016

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310,
              February 2009, <>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [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,


   The authors wish to thank Sam Aldrin, Manav Bhatia, and Carlos
   Pignataro for input essential to defining the needed functionality.

Authors' Addresses

   Les Ginsberg
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, CA  95035
   United States of America


   Nobo Akiya
   Big Switch Networks


   Mach(Guoyi) Chen


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