RFC 7607

Codification of AS 0 Processing

📅 published August 2015, from ietf

RFC 7607: Codification of AS 0 Processing ✨

Okay bestie, this is RFC 7607, and it's a Standards Track doc from August 2015 🎀. It's from the Internet Engineering Task Force (IETF) and its ISSN is 2070-1721. It updates RFC 4271 and doesn't obsolete anything. The authors are Warren Kumari (Google), Randy Bush (Internet Initiative Japan), Heather Schiller (Google), and Keyur Patel (Cisco Systems) 💖. Full author details are at the bottom, in the Authors' Addresses section.

Abstract

Okay so this doc updates RFC 4271 and officially bans Autonomous System (AS) 0 from showing up in the Border Gateway Protocol (BGP) OPEN, AS_PATH, AS4_PATH, AGGREGATOR, and AS4_AGGREGATOR attributes, plus the BGP UPDATE message 🚫✨.

Status of This Memo

This is an Internet Standards Track document 🦋.

It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more info on Internet Standards, check Section 2 of RFC 5741 💅.

For the current status of this doc, any errata, and how to give feedback, go to http://www.rfc-editor.org/info/rfc7607 🌸.

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved 💜.

This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stood on the date it was published. Read these carefully, because they spell out your rights and restrictions. Code Components pulled from this doc must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, as described in the Simplified BSD License 📜.

Table of Contents

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
  1.1.  Requirements Notation . . . . . . . . . . . . . . . . . .   2
2.  Behavior  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
  5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
  5.2.  Informative References  . . . . . . . . . . . . . . . . .   4
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   4
Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1. Introduction

Okay so AS 0 was listed in the IANA Autonomous System Number Registry as "Reserved - May be use [sic] to identify non-routed networks" ([IANA.AS_Numbers]) 🙈.

Next up, [RFC6491] says AS 0 in a Route Origin Attestation (ROA) marks a prefix, plus all its more specific prefixes, as not to be used in a routing context. So a resource holder can say "don't route this prefix (or anything more specific)" by publishing a ROA that lists AS 0 as the only origin 🛑. To actually respond to that signal, BGP implementations need to not accept or propagate routes that contain AS 0 💀.

Here's the tea ☕: no clear statement that AS 0 was banned could be found in any BGP spec. This doc fixes that omission, mostly for the AS_PATH. It's an update to the error handling procedures in Sections 6.2 and 6.3 of [RFC4271], since it spells out the behavior when AS 0 is present 🔥.

At least two implementations already throw away routes containing AS 0, and this doc makes that behavior official 👑.

1.1. Requirements Notation

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 [RFC2119] 🎀.

2. Behavior

A BGP speaker MUST NOT originate or propagate a route with an AS number of zero in the AS_PATH, AS4_PATH, AGGREGATOR, or AS4_AGGREGATOR attributes. Main character rule, no exceptions 💅.

An UPDATE message that contains the AS number of zero in the AS_PATH or AGGREGATOR attribute MUST be considered as malformed and be handled by the procedures specified in [RFC7606] 🚨.

An UPDATE message that contains the AS number of zero in the AS4_PATH or AS4_AGGREGATOR attribute MUST be considered as malformed and be handled by the procedures specified in [RFC6793] 🚨.

If a BGP speaker receives zero as the peer AS in an OPEN message, it MUST abort the connection and send a NOTIFICATION with Error Code "OPEN Message Error" and subcode "Bad Peer AS" (see Section 6 of [RFC4271]). A router MUST NOT initiate a connection claiming to be AS 0. Absolutely not 🙅‍♀️.

Authors of future protocol extensions that carry the Autonomous System number are encouraged to keep in mind that AS 0 is reserved and to provide clear direction on how to handle AS 0 🧚.

3. IANA Considerations

The IANA has updated the registry for "16-bit Autonomous System Numbers" so that the entry for AS 0 is simply "Reserved" 📋✨.

4. Security Considerations

Lowkey the most iconic section 😭. By letting a Resource Public Key Infrastructure (RPKI) resource holder issue a ROA saying AS 0 is the only valid origin for a route, we let them say that a particular address resource isn't in use 🌈. And by making sure every implementation that sees AS 0 in a route ignores that route, we stop a malicious party from announcing routes with AS 0 to try to hijack those resources 🦹‍♀️🚫. That's a serious threat, so no notes on this one, just respect 🫶.

Also, by standardizing how to handle an AS_PATH (or AS4_PATH) that contains AS 0, this doc makes the behavior way better defined 🍓.

5. References

5.1. Normative References

[IANA.AS_Numbers]
           IANA, "Autonomous System (AS) Numbers",
           <http://www.iana.org/assignments/as-numbers>.

[RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119,
           DOI 10.17487/RFC2119, March 1997,
           <http://www.rfc-editor.org/info/rfc2119>.

[RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
           Border Gateway Protocol 4 (BGP-4)", RFC 4271,
           DOI 10.17487/RFC4271, January 2006,
           <http://www.rfc-editor.org/info/rfc4271>.

[RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
           Autonomous System (AS) Number Space", RFC 6793,
           DOI 10.17487/RFC6793, December 2012,
           <http://www.rfc-editor.org/info/rfc6793>.

[RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
           Patel, "Revised Error Handling for BGP UPDATE Messages",
           RFC 7606, DOI 10.17487/RFC7606, July 2015,
           <http://www.rfc-editor.org/info/rfc7606>.

5.2. Informative References

[RFC6491]  Manderson, T., Vegoda, L., and S. Kent, "Resource Public
           Key Infrastructure (RPKI) Objects Issued by IANA",
           RFC 6491, DOI 10.17487/RFC6491, February 2012,
           <http://www.rfc-editor.org/info/rfc6491>.

Acknowledgements

The authors want to thank Elwyn Davies, Enke Chen, Brian Dickson, Bruno Decraene, Robert Raszuk, Jakob Heitz, Danny McPherson, Chris Morrow, iLya, John Scudder, Jeff Tantsura, Daniel Ginsburg, and Susan Hares 🫶. Sorry if we missed anyone, it wasn't on purpose 🥺.

Authors' Addresses

Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA  94043
United States

Email: warren@kumari.net


Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, WA  98110
United States

Email: randy@psg.com


Heather Schiller
Google
1600 Amphitheatre Parkway
Mountain View, CA  94043
United States

Email: has@google.com


Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA  95134
United States

Email: keyupate@cisco.com
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