RFC 2842

RFC 2842: Capabilities Advertisement with BGP-4 🎀

okay bestie, this one is a Standards Track doc from May 2000 📅 written by Ravi Chandra (Redback Networks Inc.) and John G. Scudder (cisco Systems) 💅 the header has no Obsoletes or Updates line, so it doesn't replace or patch anything else 🦋

Status of This Memo ✨

this is an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 💖 check the current edition of "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol 🌸 distribution of this memo is unlimited 🫶

Copyright Notice 🌈

Copyright (C) The Internet Society (2000). All Rights Reserved. 💜

Abstract 🧚

okay so right now BGP-4 [BGP-4] says that when a BGP speaker gets an OPEN message with one or more unrecognized Optional Parameters, the speaker MUST terminate BGP peering 😭 that makes introducing new capabilities in BGP super messy 💀

this doc defines a new Optional Parameter called Capabilities 🎀 it's meant to make new capabilities way easier to roll out, because it gives you graceful capability advertisement without having to kill the peering session 🦋✨

1. Overview of Operations 🌸

when a BGP speaker that supports capabilities advertisement sends an OPEN message to its peer, the message MAY include an Optional Parameter called Capabilities 💅 that parameter lists the capabilities the speaker supports 🫶

a BGP speaker figures out what its peer supports by checking the list of capabilities in the Capabilities Optional Parameter that rides along with the OPEN message it gets from the peer 👀

a BGP speaker that supports a particular capability MAY use that capability with its peer, but only after it has worked out (like we just talked about) that the peer supports it too 🔥

if a speaker sends an OPEN message with the Capabilities Optional Parameter and gets back a NOTIFICATION message with the Error Subcode set to Unsupported Optional Parameter, then the speaker has figured out its peer doesn't support capabilities advertisement 😭 in that case the speaker SHOULD attempt to re-establish the BGP connection with the peer without sending the Capabilities Optional Parameter to it 🙈

if a BGP speaker that supports a certain capability finds out its peer doesn't support it, the speaker MAY send a NOTIFICATION message to the peer and terminate peering ⭐ 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 it and terminate is a local call the speaker makes 💅 and such peering SHOULD NOT be re-established automatically 🛑

2. Capabilities Optional Parameter (Parameter Type 2): 🦋

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

the parameter holds one or more triples <Capability Code, Capability Length, Capability Value>, and each triple is encoded like this 👑

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

here's what each field does 🧚

Capability Code: a one octet field that unambiguously identifies individual capabilities 🔥

Capability Length: a one octet field that contains the length of the Capability Value field in octets 🌸

Capability Value: a variable length field that gets interpreted based on the value of the Capability Code field 💖

a particular capability, identified by its Capability Code, MAY occur more than once within the Optional Parameter 🫶 (yes, you can repeat yourself, no cap) ✨

3. Extensions to Error Handling 🍓

this doc defines a new Error Subcode, Unsupported Capability 💅 its value is 7 🎀 the Data field in the NOTIFICATION message lists the set of capabilities that caused the speaker to send the message 🦋 each of those capabilities is encoded the same way it was encoded in the received OPEN message 💜

4. IANA Considerations 🌈

Section 4 defines a Capability Optional Parameter along with an Capability Code field. IANA is expected to create and maintain the registry for Capability Code values 🧚 Capability Code value 0 is reserved 🔒 Capability Code values 1 through 63 are to be assigned by IANA using the "IETF Consensus" policy defined in RFC2434 🫶 Capability Code values 64 through 127 are to be assigned by IANA using the "First Come First Served" policy defined in RFC2434 🌸 and Capability Code values 128 through 255 are for "Private Use" as defined in RFC2434 👑

5. Security Considerations 🚨

okay this part is serious, bestie 😭 this extension to BGP does NOT change the underlying security issues that already exist in BGP [Heffernan] 💀 so don't think adding capabilities fixes security stuff, because it doesn't 🙈

6. Acknowledgements 🫶

the authors would like to thank members of the IDR Working Group for their review and comments 💖

7. 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.

8. 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

9. Full Copyright Statement 💜

Copyright (C) The Internet Society (2000). All Rights Reserved.

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 🫶🎀