RFC 9247

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

📅 published June 2022, from ietf

RFC 9247: BGP - Link State (BGP-LS) Extensions for Seamless Bidirectional Forwarding Detection (S-BFD) 🦋

Okay bestie, so this is RFC 9247 💖 It's a Standards Track doc, which means it's an official Internet standard and not just a vibe. It came out in June 2022 and was written by Z. Li and S. Zhuang (Huawei), K. Talaulikar, Ed. (Arrcus, Inc.), S. Aldrin (Google, Inc.), J. Tantsura (Microsoft), and G. Mirsky (Ericsson). The ISSN is 2070-1721 ✨ The header has no Obsoletes or Updates line, so it doesn't replace or change any other RFC.

Abstract 🌸

Okay so Seamless Bidirectional Forwarding Detection (S-BFD) is giving simplified. It defines an easier way to use Bidirectional Forwarding Detection (BFD) where a big chunk of the negotiation stuff is cut out 🙈 That means quick provisioning and more control and flexibility for the network nodes that start the path monitoring. The link-state routing protocols (IS-IS and OSPF) have already been extended to advertise the S-BFD Discriminators.

This document defines extensions to the BGP - Link State (BGP-LS) address family so the S-BFD Discriminators' info can travel over BGP ✨

Status of This Memo 📋

This is an Internet Standards Track document.

It's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community. It went through public review and was approved for publication by the Internet Engineering Steering Group (IESG). For more on Internet Standards, check Section 2 of RFC 7841.

For the current status, any errata, and how to give feedback, go to https://www.rfc-editor.org/info/rfc9247 🔗

Copyright Notice 💅

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they were on the publication date. Read these carefully, because they spell out your rights and restrictions for this doc. Code Components pulled out of this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come 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 ✨

So S-BFD [RFC7880] is the simplified mechanism for BFD [RFC5880], again with a lot of the negotiation stuff eliminated. You get quick provisioning and better control for the nodes initiating path monitoring 💖

Here's the setup. For end-to-end monitoring of a service path with S-BFD, the headend node (i.e., Initiator) needs to know the S-BFD Discriminator of the destination/tail-end node (i.e., Responder) for that service. The link-state routing protocols (IS-IS [RFC7883] and OSPF [RFC7884]) have been extended to advertise S-BFD Discriminators, so an Initiator can learn the S-BFD Discriminator for every Responder within its IGP area/level, or optionally across the whole domain. Networks often get split into several IGP domains for scaling and ops reasons, and the endpoints that need end-to-end S-BFD monitoring often end up spread across those domains 😭

This is where BGP-LS [RFC7752] comes in. It lets you collect and distribute IGP link-state topology info over BGP sessions across IGP areas/levels and domains. So a node's S-BFD Discriminator(s) can ride along with the topology info through BGP-LS, across IGP domains and even across multiple Autonomous Systems (ASes) inside one administrative domain 🌈

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

2. Terminology 🎀

This memo uses 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. Lowercase versions don't count 🙈

3. BGP-LS Extensions for S-BFD Discriminators 🦋

Okay, so [RFC7752] says BGP-LS specifies the Node Network Layer Reachability Information (NLRI) for advertising nodes and their attributes using the BGP-LS Attribute. The S-BFD Discriminators of a node are treated as a node-level attribute and get advertised that way 💅

This document defines a new BGP-LS Attribute TLV called "S-BFD Discriminators TLV". Here's how it's laid out:

    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

Here's what each field means:

Type: 1032
Length: variable. It MUST be a minimum of 4 octets, and it increments by 4 octets for each additional discriminator. Bestie, this one's a must-do 😤
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 tied to the Node NLRI that originates the matching underlying IGP TLV/sub-TLV, as described below. The info comes from the protocol-specific advertisements like this:

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 "IS-IS TLV/Sub-TLV" column in that registry doesn't need any value, and it 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 in this document augment the existing IGP topology info that gets distributed via BGP-LS [RFC7752]. The procedures and extensions here don't change BGP protocol operations or management beyond what's covered in "Manageability Considerations" (Section 6) of [RFC7752]. Specifically, the malformed NLRIs attribute tests in "Fault Management" (Section 6.2.2) of [RFC7752] now cover the new TLV for the BGP-LS NLRI in this document 🍓

6. Security Considerations 💀

Okay, this section is serious, so read it closely 🙈

The new protocol extensions in this document augment the existing IGP topology info that can be distributed via BGP-LS [RFC7752]. The procedures and extensions here don't change the BGP security model beyond what's discussed in "Security Considerations" (Section 8) of [RFC7752]. That's the part about limiting which nodes and consumers the topology info gets shared with, down to trusted entities inside one administrative domain 🔐

The TLV in this document is used to propagate IGP-defined info (see [RFC7883] and [RFC7884]). It represents the info used to set up S-BFD sessions. The IGP instances that originate this info 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]. Please go read that, bestie 💀

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 Acknowledgements section isn't in this part, so it'll show up in part 2 💖

Authors' Addresses 🎀

The Authors' Addresses section isn't in this part either, so we'll finish it up in part 2 🫶

Acknowledgements ✨

okay bestie, the authors wanna give a huge shoutout to Nan Wu 🫶 for his contributions to this work. They also want to thank Gunter Van de Velde and Thomas Fossati for their reviews 💖, Jeff Haas for the shepherd review 🌸, and Alvaro Retana for the AD review of this document 👑. The whole crew really made this happen!

Authors' Addresses 🎀

Here's who wrote this beauty, with their contact info. Slide into their inbox if you've got questions 💅

Zhenbin Li

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

That's the whole RFC, bestie! 🌈🦋 Ketan was the editor, so they get the main character crown 👑 and everyone else gets a standing ovation 😭🫶

📦 where this page comes from

ietf: rfc9247 2022-06
💖 girlified by claude-haiku-5-5 on 2026-10-19: a language model's rewrite of the original, under its terms