idr W. Kumari
Internet-Draft Google
Intended status: Standards Track R. Bush
Expires: May 30, 2012 Internet Initiative Japan
H. Schiller
November 29, 2011

Codification of AS 0 processing.


This document proscribes the use of AS 0 in BGP OPEN and AS_PATH / AS4_PATH BGP attribute.

Status of This Memo

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This Internet-Draft will expire on May 30, 2012.

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Table of Contents

1. Introduction

Autonomous System 0 is listed in the IANA Autonomous System Number Registry as "Reserved - May be use to identify non-routed networks" ([IANA.AS_Numbers]).

[I-D.ietf-sidr-iana-objects] specifies that AS number zero in a ROA is used to mark an NLRI which is to be marked as Invalid.

No clear statement that AS 0 was proscribed could be found in any BGP specification.

As at least two implementations discard routes containing AS 0 (and to allow approaches such as the above) 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].

2. Behavior

This document specifies that a BGP speaker MUST NOT originate or propagate a route with an AS number of zero. If a BGP speaker receives a route which has an AS number of zero in the AS_PATH (or AS4_PATH) attribute, it SHOULD be logged and treated as a WITHDRAW. This same behavior applies to routes containing zero as the Aggregator or AS4 Aggregator.

In addition 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 [RFC4271] Section 6.2). Obviously enough, a router MUST NOT initiate a connection claiming to be AS number zero.

3. IANA Considerations

The IANA is requested to update the Reference for number 0 in the "Autonomous System (AS) Numbers" registry to reference this document.

4. Security Considerations

By allowing resource holders to say 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, and security gotchas often lurk in the undefined spaces.

5. Acknowledgements

The authors wish to thank Enke Chen, Robert Raszuk, Danny McPherson, Keyur Patel, John Scudder. Apologies to those we may have missed, it was not intentional.

6. References

6.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Rekhter, Y., Li, T. and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.
[IANA.AS_Numbers] IANA, "Autonomous System (AS) Numbers", .

6.2. Informative References

[I-D.ietf-sidr-iana-objects] Manderson, T, Vegoda, L and S Kent, "RPKI Objects issued by IANA", Internet-Draft draft-ietf-sidr-iana-objects-03, May 2011.

Appendix A. Changes / Author Notes.

[RFC Editor: Please remove this section before publication ]

Draft accepted as IDR Doc, notes reset. Please see notes for draft-wkumari-idr-as0.xml for prior comments.

Changes -00.

Authors' Addresses

Warren Kumari Google 1600 Amphitheatre Parkway Mountain View, CA, 94043 US EMail:
Randy Bush Internet Initiative Japan 5147 Crystal Springs Bainbridge Island, WA, 98110 US EMail:
Heather Schiller Verizon 22001 Loudoun County Parkway Ashburn, 20147 US EMail: