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rfc:rfc7607

Internet Engineering Task Force (IETF) W. Kumari Request for Comments: 7607 Google Updates: 4271 R. Bush Category: Standards Track Internet Initiative Japan ISSN: 2070-1721 H. Schiller

                                                                Google
                                                              K. Patel
                                                         Cisco Systems
                                                           August 2015
                  Codification of AS 0 Processing

Abstract

 This document updates RFC 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 in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://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 to BCP 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 2015

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

 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 Sections 6.2 and 6.3 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 2015

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.
 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.
 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 2015

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 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 2015

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

Kumari, et al. Standards Track [Page 5]

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