RFC 5668

4-Octet AS Specific BGP Extended Community

📅 published October 2009, from ietf

RFC 5668: 4-Octet AS Specific BGP Extended Community 💖

okay bestie, the header is giving: this is RFC 5668 from the Network Working Group 🎀, dated October 2009. It's on the Standards Track 👑, which means it's an actual Internet standard and not just a vibe. The authors are Yakov Rekhter (Juniper Networks), Srihari R. Sangli (Cisco Systems), and Dan Tappan (listed as a consultant). It doesn't list any Obsoletes or Updates entries in its header, so it isn't replacing or changing another RFC. ✨

Abstract

this doc defines a brand new kind of BGP extended community 🦋, one that carries a 4-octet Autonomous System (AS) number. no cap, that's the whole pitch.

Status of This Memo

this document specifies an Internet standards track protocol for the Internet community, and asks for discussion and suggestions for improvements 🫶. for the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1) 📚. distribution of this memo is unlimited 💅.

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 they were in effect on the date of publication. pls review those docs carefully, because they describe your rights and restrictions for this document 🙈. code components pulled out of 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 BSD License.

this document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. the people controlling the copyright in some of that material may not have granted the IETF Trust the right to allow modifications outside the IETF Standards Process 😭. so unless you get an adequate license from those copyright holders, 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. the only exceptions are formatting it for publication as an RFC, or translating it into languages other than English.

1. Introduction 🧚

this doc defines a new type of BGP extended community [RFC4360]: a 4-octet AS specific extended community 💜. it's basically the same as the 2-octet AS specific extended community, except this one can carry a 4-octet Autonomous System number. it's the upgrade we needed 🔥.

1.1. 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] 🎀. these are the official BCP 14 words, so read them carefully.

2. 4-Octet AS Specific Extended Community 🍓

this is an extended type with a Type field that's 2 octets and a Value field that's 6 octets ✨.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x02 or 0x42  |   Sub-Type    |    Global Administrator       :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   : Global Administrator (cont.)  |    Local Administrator        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

the high-order octet of this extended type is either 0x02 (for transitive communities) or 0x42 (for non-transitive communities) 🦋. the low-order octet is used to indicate sub-types 💅.

the Value field has 2 sub-fields:

Global Administrator sub-field: 4 octets 👑
- this sub-field contains a 4-octet Autonomous System number assigned by IANA.
Local Administrator sub-field: 2 octets 🌸
- the organization identified by the Autonomous System number in the Global Administrator sub-field can encode any information in this sub-field. the format and meaning of the value encoded here should be defined by the sub-type of the community.

3. Considerations for 2-Octet Autonomous Systems 🙈

as per [RFC4893], a 2-octet Autonomous System number can be converted into a 4-octet Autonomous System number by setting the 2 high-order octets of the 4-octet field to zero 🧠.

so, at least in principle, an Autonomous System that uses a 2-octet Autonomous System number could use either 2-octet or 4-octet AS specific extended communities. this is undesirable 💀, because both communities would be treated as different, even if they had the same Sub-Type and Local Administrator values.

so, for backward compatibility with existing deployments and to avoid inconsistencies between 2-octet and 4-octet specific extended communities, Autonomous Systems that use 2-octet Autonomous System numbers SHOULD use 2-octet AS specific extended communities rather than 4-octet AS specific extended communities 🫶. this one's a big deal, bestie.

4. IANA Considerations 📚

this document defines a class of extended communities, called 4-octet AS specific extended communities, for which IANA has created and will maintain a registry entitled Four-octet AS Specific Extended Community ✨. all the communities in this class are of extended Types. future assignments are made using the "First Come First Served" policy defined in [RFC5226] 🎀. the Type values for the transitive communities of this class are 0x0200-0x02ff, and for the non-transitive communities they are 0x4200-0x42ff 💜. assignments consist of a name and the value.

this document makes the following assignments for the 4-octet AS specific extended community:

   Name                                     Type Value
   ----                                     ----------
   four-octet AS specific Route Target       0x0202
   four-octet AS specific Route Origin       0x0203

5. Security Considerations 💀

ok this section is serious, so listen up 🚨. this document does not add new security issues. all the security considerations for BGP extended communities apply here 🔒. at the time this document was written, there were significant efforts underway to improve the security properties of BGP. for examples of documents produced up to that point of publication, see [RFC4593] and [SIDR] 🛡️.

There is a potential serious issue if a malformed, optional transitive attribute is received. this issue, and the steps to avoid it, are discussed in [OPT_TRANS]. pls go read that one, fr fr 😭.

6. Acknowledgements 🫶

thanks to Bruno Decraene for his contributions to this document 💖.

7. References 📖

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, February 2006.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number Space", RFC 4893, May 2007.

7.2. Informative References

[OPT_TRANS] Scudder, J., and E. Chen, "Error Handling for Optional Transitive BGP Attributes", Work in Progress, April 2009.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to Routing Protocols", RFC 4593, October 2006.
[SIDR] Lepinski, M. and S. Kent, "An Infrastructure to Support Secure Internet Routing", Work in Progress, July 2009.

Authors' Addresses 💌

Yakov Rekhter, Juniper Networks, Inc., EMail: yakov@juniper.net
Srihari R. Sangli, Cisco Systems, Inc., EMail: rsrihari@cisco.com
Dan Tappan, Boxborough MA, EMail: Dan.Tappan@Gmail.com

that's the whole RFC, bestie 🌈👑 it's a short one, but it's iconic. ✨

📦 where this page comes from

ietf: rfc5668 2009-10
💖 girlified by claude-haiku-5-5 on 2026-10-17: a language model's rewrite of the original, under its terms