RFC 7884

OSPF Extensions to Advertise Seamless Bidirectional Forwarding Detection (S-BFD) Target Discriminators

📅 published July 2016, from ietf

Part 1 of 2 🎀

Title Block 🦋

Request for Comments: 7884, the one and only, published in July 2016 📅
Category: Standards Track, so it's an official Internet standard 👑
ISSN: 2070-1721
Authors: C. Pignataro (Cisco), M. Bhatia (Ionos Networks), S. Aldrin (Huawei Technologies), and T. Ranganath (Nokia) 💜
Obsoletes and updates: it doesn't list anything it obsoletes or updates 🌸
Title: OSPF Extensions to Advertise Seamless Bidirectional Forwarding Detection (S-BFD) Target Discriminators 🌈

Abstract ✨

Okay so this doc adds a brand-new OSPF Router Information (RI) TLV 🧚. It lets OSPF routers flood the Seamless Bidirectional Forwarding Detection (S-BFD) Discriminator values tied to a target network identifier. And it works for both OSPFv2 and OSPFv3, which is so convenient 💅.

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 got approved for publication by the Internet Engineering Steering Group (IESG). If you want more info on Internet Standards, check Section 2 of RFC 7841 🫶.

For the current status of this document, any errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc7884 🔗.

Copyright Notice ©️

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as in effect on the date of publication. Please read these carefully, because they spell out your rights and restrictions for 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 they come without warranty as described in the Simplified BSD License 📜.

Table of Contents 🗂️

1. Introduction ....................................................3
   1.1. Relationship between OSPF and S-BFD ........................3
2. Implementation ..................................................3
   2.1. S-BFD Discriminator TLV ....................................4
   2.2. Flooding Scope .............................................4
3. Backward Compatibility ..........................................5
4. Security Considerations .........................................5
5. IANA Considerations .............................................6
6. References ......................................................6
   6.1. Normative References .......................................6
   6.2. Informative References .....................................6
Acknowledgements ...................................................7
Authors' Addresses .................................................7

1. Introduction 🌸

Seamless Bidirectional Forwarding Detection (S-BFD), specified in [RFC7880], is a simplified way to use BFD where a bunch of negotiations just get eliminated 🙌. The trick is 4-octet discriminators, which are unique within an administrative domain, and they're how you identify the network targets 🎯. These S-BFD Discriminators can be advertised by the IGPs, and this doc is all about OSPF 🧚. Specifically, it defines a new TLV (called the S-BFD Discriminator TLV) that gets carried within the OSPF Router Information (RI) Link State Advertisement (LSA) [RFC7770] 💖.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119] 🤓.

1.1. Relationship between OSPF and S-BFD 🫧

This doc implicitly sets up a relationship between OSPF and S-BFD 💜. S-BFD assigns one or more discriminators to each S-BFD reflector node. OSPF then learns about these from S-BFD and floods them out in the newly defined TLV. Once that info is flooded, it's stored in all the OSPF nodes, so S-BFD initiators can map out target nodes to target discriminators and build the S-BFD probe 🎀.

When multiple S-BFD Discriminators are advertised, how a given discriminator maps to a specific use case is out of scope for this document 🙈.

2. Implementation 🛠️

This extension uses the Router Information (RI) Opaque LSA, defined in [RFC7770], for both OSPFv2 [RFC2328] and OSPFv3 [RFC5340]. It does this by defining a new OSPF Router Information (RI) TLV: the S-BFD Discriminator TLV 🦋.

The S-BFD Discriminator TLV is OPTIONAL 🫶. When a router receives the TLV, it may decide to install the S-BFD Discriminator in the BFD target identifier table 💅.

If there are multiple instances of the OSPFv2/OSPFv3 Router Information LSA, the S-BFD Discriminators for an OSPF router are the union of all discriminators advertised in all instances of the S-BFD Discriminator TLV (see Section 2.1) across all advertised non-MaxAge OSPF Router Information LSAs ✨.

2.1. S-BFD Discriminator TLV 🧩

Here's the format of the S-BFD Discriminator TLV, and it's giving very neat boxes 📦:

    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)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Here's what each field means 👇:

Type is the S-BFD Discriminator TLV Type, which is 11 🔢.
Length is the total length of the discriminator(s) in the Value field, in octets. Each discriminator is 4 octets, so the Length is four times the number of discriminators in the TLV. There's no optional padding for this field 🍓.
Discriminator(s) are the Value field of the TLV, holding the S-BFD network target Discriminator value or values 💜.

Routers that don't recognize the S-BFD Discriminator TLV Type will ignore the TLV [RFC7770], so they won't learn S-BFD Discriminators via OSPF 🙃.

2.2. Flooding Scope 🌊

The S-BFD Discriminator TLV is advertised within OSPFv2 Router Information LSAs (Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router Information LSAs (function code of 12), which are defined in [RFC7770]. So the elements of this procedure are inherited from those defined in [RFC7770] 🧚.

The flooding scope is controlled by the Opaque LSA type (as defined in [RFC5250]) in OSPFv2, and by the S1/S2 bits (as defined in [RFC5340]) in OSPFv3 🎀. If the flooding scope is area local, then the S-BFD Discriminator TLV MUST be carried within an OSPFv2 type 10 Router Information LSA, or an OSPFv3 Router Information LSA with the S1 bit set and the S2 bit clear 🏡. If the flooding scope is the entire IGP domain, then the S-BFD Discriminator TLV MUST be carried within an OSPFv2 type 11 Router Information LSA, or an OSPFv3 Router Information LSA with the S1 bit clear and the S2 bit set 🌍.

When the S-BFD reflector is deactivated, the OSPF speaker advertising a particular S-BFD Discriminator MUST originate a new Router Information LSA that no longer includes the corresponding S-BFD Discriminator TLV, provided there are other TLVs in the LSA. If there are no other TLVs in the LSA, it MUST either send an empty Router Information LSA or purge it by prematurely aging it 🫠.

For intra-area reachability, the S-BFD Discriminator TLV information about a specific target identifier is only considered current and usable when the router advertising that information is itself reachable via OSPF calculated paths in the same area as the LSA in which the S-BFD Discriminator TLV appears 🗺️. For domain-wide flooding, meaning the originator is sitting in a remote area, the mechanism described in Section 5 of [RFC5250] should be used 💫.

The S-BFD Discriminators may change when enabling the S-BFD functionality or through an explicit configuration event, but those changes are expected to happen very rarely 🌙. Whenever that info changes, the S-BFD Discriminator TLV in OSPF has to be advertised 📣.

A change in information in the S-BFD Discriminator TLV MUST NOT trigger any SPF computations at a receiving router 🙅‍♀️. Iconic behaviour, honestly 💅.

6.2. Informative References

[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, July 2008, <http://www.rfc-editor.org/info/rfc5250>. 📚✨

Acknowledgements 🫶

okay so the authors wanna give a huge shoutout 📣 to Nobo Akiya, Les Ginsberg, Mach Chen, and Peter Psenak for their insightful comments and useful suggestions. y'all really made this doc better, periodt 💖

Authors' Addresses 💌

Carlos Pignataro 🦋 Cisco Systems, Inc. Email: cpignata@cisco.com

Manav Bhatia 🌸 Ionos Networks Email: manav@ionosnetworks.com

Sam Aldrin 🧚 Huawei Technologies Email: aldrin.ietf@gmail.com

Trilok Ranganath 💜 Nokia Email: trilok.ranganatha@nokia.com

📦 where this page comes from

ietf: rfc7884 2016-07
💖 girlified by claude-haiku-5-5 on 2026-10-18: a language model's rewrite of the original, under its terms