Codification of AS 0 processing.
draft-ietf-idr-as0-00

Abstract

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

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http:/⁠/⁠datatracker.ietf.org/⁠drafts/⁠current/⁠.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

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

Copyright Notice

Copyright (c) 2011 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.

Table of Contents

• 1. Introduction
• 1.1. Requirements notation
• 2. Behavior
• 3. IANA Considerations
• 4. Security Considerations
• 5. Acknowledgements
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Appendix A. Changes / Author Notes.
• Authors' Addresses

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

6.2. Informative References

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.

• Added AS4_PATH -- Robert Raszuk.
• Change "bgp listener" to "bgp speaker" -- Enke Chen
• Consistent use of AS_PATH (v., AS-PATH and AS PATH) -- Danny McPherson
• New text for Sec 2 P1 -- Enke / Keyur / Scudder, http://www.ietf.org/mail-archive/web/idr/current/msg05786.html
• I made a boo boo -- I had the file open in 2 editors, made changes in one and overwrote them by saving on the other, then checked the broken one into SVN. Apologies to all whose comments I may have missed...

Authors' Addresses