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Internet Engineering Task Force (IETF)                         W. KumariRequest for Comments: 7607                                        GoogleUpdates:4271                                                    R. BushCategory: Standards Track                      Internet Initiative JapanISSN: 2070-1721                                              H. Schiller                                                                  Google                                                                K. Patel                                                           Cisco Systems                                                             August 2015Codification of AS 0 ProcessingAbstract   This document updatesRFC 4271 and proscribes the use of Autonomous   System (AS) 0 in the Border Gateway Protocol (BGP) OPEN, AS_PATH,   AS4_PATH, AGGREGATOR, and AS4_AGGREGATOR attributes in the BGP UPDATE   message.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7607.Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to 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 are provided without warranty as   described in the Simplified BSD License.Kumari, et al.               Standards Track                    [Page 1]

RFC 7607                     AS 0 Processing                 August 2015Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Requirements Notation . . . . . . . . . . . . . . . . . .22.  Behavior  . . . . . . . . . . . . . . . . . . . . . . . . . .33.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .34.  Security Considerations . . . . . . . . . . . . . . . . . . .35.  References  . . . . . . . . . . . . . . . . . . . . . . . . .45.1.  Normative References  . . . . . . . . . . . . . . . . . .45.2.  Informative References  . . . . . . . . . . . . . . . . .4   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .4   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .51.  Introduction   Autonomous System 0 was listed in the IANA Autonomous System Number   Registry as "Reserved - May be use [sic] to identify non-routed   networks" ([IANA.AS_Numbers]).   [RFC6491] specifies that AS 0 in a Route Origin Attestation (ROA) is   used to mark a prefix and all its more specific prefixes as not to be   used in a routing context.  This allows a resource holder to signal   that a prefix (and the more specifics) should not be routed by   publishing a ROA listing AS 0 as the only origin.  To respond to this   signal requires that BGP implementations not accept or propagate   routes containing AS 0.   No clear statement that AS 0 was proscribed could be found in any BGP   specification.  This document corrects this omission, most   importantly in the case of the AS_PATH.  This represents an update to   the error handling procedures given in Sections6.2 and6.3 of   [RFC4271] by specifying the behavior in the presence of AS 0.   At least two implementations discard routes containing AS 0, and this   document codifies this behavior.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].Kumari, et al.               Standards Track                    [Page 2]

RFC 7607                     AS 0 Processing                 August 20152.  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.   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" (seeSection 6 of   [RFC4271]).  A router MUST NOT initiate a connection claiming to be   AS 0.   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   By allowing a Resource Public Key Infrastructure (RPKI) resource   holder to issue a ROA saying that AS 0 is the only valid origin for a   route, we allow them to state that a particular address resource is   not in use.  By ensuring that all implementations that see AS 0 in a   route ignore that route, we prevent a malicious party from announcing   routes containing AS 0 in an attempt to hijack those resources.   In addition, by standardizing the behavior upon reception of an   AS_PATH (or AS4_PATH) containing AS 0, this document makes the   behavior better defined.Kumari, et al.               Standards Track                    [Page 3]

RFC 7607                     AS 0 Processing                 August 20155.  References5.1.  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 wish 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.  Apologies to those we may have missed; it was not   intentional.Kumari, et al.               Standards Track                    [Page 4]

RFC 7607                     AS 0 Processing                 August 2015Authors' 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.comKumari, et al.               Standards Track                    [Page 5]