RFC 3392

Capabilities Advertisement with BGP-4

📅 published November 2002, from ietf

RFC 3392: Capabilities Advertisement with BGP-4 🦋

Okay bestie, this one is a Standards Track doc from November 2002 💅 It was written by R. Chandra (Redback Networks) and J. Scudder (Cisco Systems), and it obsoletes RFC 2842, so if you see 2842 floating around, this is the newer, cleaner version 🎀

Network Working Group, Request for Comments: 3392

Status of This Memo 📜

Okay so this doc is an Internet standards track protocol for the Internet community, and the authors are literally asking for discussion and suggestions for improvements 🫶 If you want to know where this protocol stands, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited, so share away 💖

Copyright Notice ©️

Abstract 🦋

This doc adds a brand new Optional Parameter called Capabilities 🎀 The goal is to make it way easier to roll out new capabilities in the Border Gateway Protocol (BGP), with graceful capability advertisement that doesn't force BGP peering to be terminated. Iconic behavior, no notes 💅

This document obsoletes RFC 2842.

1. Introduction ✨

Here's the tea 🍵 Right now, BGP-4 says that if a BGP speaker gets an OPEN message with one or more unrecognized Optional Parameters, the speaker must terminate BGP peering. That makes it really hard to add new capabilities to BGP, and honestly it's giving stuck 😭

2. Specification of Requirements 🔥

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]. Read those carefully, bestie, they're the rules of the game 🧚

3. Overview of Operations 🌈

So when a BGP speaker [BGP-4] that supports capabilities advertisement sends an OPEN message to its BGP peer, the message MAY include an Optional Parameter called Capabilities. That parameter lists all the capabilities the speaker supports 💜

A BGP speaker figures out what its peer can do by checking the list of capabilities in the Capabilities Optional Parameter that rides along with the OPEN message it gets from that peer. Main character energy, knowing your friend's skills 👑

Once a speaker has found out (the way we just talked about) that its peer supports a particular capability, the speaker that supports that capability may use it with that peer ✨

If a speaker sends an OPEN message that carries the Capabilities Optional Parameter, and the response is a NOTIFICATION message with the Error Subcode set to Unsupported Optional Parameter, then the speaker has learned that its peer doesn't support capabilities advertisement. In that case the speaker SHOULD attempt to re-establish a BGP connection with the peer, this time without sending the Capabilities Optional Parameter to the peer 🙈

Now, if a BGP speaker that supports a certain capability finds out that its peer doesn't support it, the speaker MAY send a NOTIFICATION message to the peer and terminate peering (see Section "Extensions to Error Handling" for more details). The Error Subcode in that message is set to Unsupported Capability. The message SHOULD contain the capability (or capabilities) that made the speaker send it. Whether to send the message and tear down peering is up to the speaker itself, it's a local call 💅 And if peering does get terminated, it SHOULD NOT be re-established automatically. Respect the boundaries, babe 🫶

4. Capabilities Optional Parameter (Parameter Type 2): 🎀

This is the Optional Parameter a BGP speaker uses to tell its BGP peer which capabilities it supports 💖

The parameter holds one or more triples, <Capability Code, Capability Length, Capability Value>, and each triple is laid out like this:

    +------------------------------+
    | Capability Code (1 octet)    |
    +------------------------------+
    | Capability Length (1 octet)  |
    +------------------------------+
    | Capability Value (variable)  |
    +------------------------------+

Here's what each field does 🦋

Capability Code

Capability Code is a one octet field that unambiguously identifies individual capabilities. It's the ID card for each capability, no mix-ups allowed 🪪

Capability Length

Capability Length is a one octet field that holds the length of the Capability Value field, in octets 📏

Capability Value

Capability Value is a variable length field, and how it gets read depends on the Capability Code field 🌸

BGP speakers SHOULD NOT include more than one instance of a capability with the same Capability Code, Capability Length, and Capability Value. Lowkey, though, if you do send duplicates, nothing breaks, because extra copies don't change what the capability means. Processing them doesn't need any special handling 🙈

BGP speakers MAY include more than one instance of a capability (identified by the Capability Code) that has a non-zero Capability Length field, but with a different Capability Value, and the Capability Length may be the same or different. How those instances get processed is specific to the Capability Code, and the document that introduces the new capability MUST describe it 🧚

5. Extensions to Error Handling ⭐

This document defines a new Error Subcode, Unsupported Capability, with a value of 7 🔥 The Data field in the NOTIFICATION message SHOULD list the set of capabilities that caused the speaker to send the message. Each of those capabilities is encoded the same way it would be in the OPEN message 💜

6. IANA Considerations 🌈

This document defines a Capability Optional Parameter along with a Capability Code field. IANA maintains the registry for Capability Code values 🗂️

Here's how the ranges are split up:

Capability Code value 0 is reserved.
Capability Code values 1 through 63 are assigned by IANA using the "IETF Consensus" policy defined in RFC 2434.
Capability Code values 64 through 127 are assigned by IANA using the "First Come First Served" policy defined in RFC 2434.
Capability Code values 128 through 255 are for "Private Use" as defined in RFC 2434.

7. Security Considerations 💀

Okay, serious moment, bestie 😭 This extension to BGP does not change the underlying security issues inherent in the existing BGP [Heffernan]. So the vibe is: this adds features, it doesn't fix or create the old security stuff. Go read [Heffernan] for that drama 🙈

8. Acknowledgements 🫶

The authors would like to thank members of the IDR Working Group for their review and comments. Teamwork makes the dream work 💖

9. Comparison with RFC 2842 💅

Besides a few minor editorial changes, this document also clarifies how to handle multiple instances of the same capability ✨

10. References 📚

   [BGP-4]      Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
                (BGP-4)", RFC 1771, March 1995.

   [Heffernan]  Heffernan, A., "Protection of BGP Sessions via the TCP
                MD5 Signature Option", RFC 2385, August 1998.

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

11. Authors' Addresses 🌸

   Ravi Chandra
   Redback Networks Inc.
   350, Holger Way
   San Jose, CA 95134

   EMail: rchandra@redback.com


   John G. Scudder
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134

   EMail: jgs@cisco.com

12. Full Copyright Statement 🔐

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement 💜

Funding for the RFC Editor function is currently provided by the Internet Society. ✨

📦 where this page comes from

ietf: rfc3392 2002-11
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