IDR J. Haas Internet-Draft Juniper Networks Intended status: Informational J. Mitchell Expires: January 16, 2014 Microsoft Corporation July 15, 2013 Reservation of Last Autonomous System (AS) Numbers draft-ietf-idr-last-as-reservation-00 Abstract This document reserves two Autonomous System numbers (ASNs) at the end of the 16 bit and 32 bit ranges, described in this document as "Last ASNs" and provides guidance to implementers and operators on their use. 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 January 16, 2014. Copyright Notice Copyright (c) 2013 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. Haas & Mitchell Expires January 16, 2014 [Page 1] Internet-Draft Last AS Reservation July 2013 1. Introduction IANA has reserved the last Autonomous System Number (ASN), 65535, of the 16 bit autonomous system number range for over a decade with the intention that it not be used by network operators running BGP [RFC4271]. Since the introduction of BGP Support for Four-Octet AS Number Space [RFC6793], IANA has also reserved the ASN of the 32 bit autonomous system number range, 4294967295. This reservation has been documented in the IANA Autonomous System Numbers Registry [IANA.AS]. Although these "Last ASNs" border on Private Use ASN ranges, they are not defined as Private Use ASNs by [I-D.ietf-idr-as-private-reservation]. This document describes the reasoning for reserving these Last ASNs and provides guidance both to operators and to implementers on their use. 2. Requirements Language 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 RFC 2119 [RFC2119]. 3. Reasons for Last ASNs Reservation The primary reason for reserving the Last ASN of both the 16 bit and 32 bit ASN ranges is that these numbers are also at the end of typical computational data structures holding the underlying number. Programmatic errors are more common when handling of end of range values, and sometimes last values (binary all ones) have been used as "magic numbers", to represent a different number or behavior. Secondly, a subset of the standard BGP communities of the last ASN of the 16 bit range, 65535, are reserved for use by Well-known communities as described in [RFC1997] and [IANA.WK]. Although this not currently true of ASN 4294967295, if there is a future need for a Special Use ASN that is not designed to be globally routable, or the associated BGP attributes (such as communities) of such an ASN, this could be a valid candidate for such purpose. This document does not prescribe any such purpose to this ASN. 4. Operational Considerations Operators MUST NOT use these Last ASNs as if they are Private Use ASNs, and SHOULD NOT use these Last ASNs for any other purpose, except a Special Uses defined elsewhere. Any other operational use of these Last ASNs could have unpredictable or undesirable results. For example; use of AS 65535 as if it were a Private Use ASN, may result in inadvertent use of BGP Well-known community values [IANA.WK], causing undesired routing behavior. Haas & Mitchell Expires January 16, 2014 [Page 2] Internet-Draft Last AS Reservation July 2013 Operators that choose to filter Private Use ASNs within the AS_PATH and AS4_PATH attributes SHOULD also filter these Last ASNs. These last ASNs MUST NOT be advertised to the global Internet within AS_PATH or AS4_PATH attributes. 5. Implementation Considerations While these Last ASNs are reserved, they remain valid ASNs from a protocol perspective. Therefore, implementations of BGP [RFC4271] SHOULD NOT treat the use of these Last ASNs as any type of protocol error. However, implementations MAY generate a local warning message indicating probable improper use of a reserved ASN. Implementations that provide tools that filter Private Use ASNs within the AS_PATH and AS4_PATH attributes MAY also include these Last ASNs. 6. IANA Considerations IANA has reserved last Autonomous System number 65535 from the "16-bit Autonomous System Numbers" registry for the reasons described in this document. IANA has also reserved last Autonomous System number 4294967295 from the "32-bit Autonomous System Numbers" registry for the reasons described in this document. This reservation has been documented in the IANA Autonomous System Numbers Registry [IANA.AS]. 7. Security Considerations This document does not introduce any additional security concerns in regards to usage of Last ASNs. Although the BGP protocol is designed to allow usage of these Last ASNs, security issues related to BGP implementation errors could be triggered by Last ASN usage. 8. References 8.1. Normative References [IANA.AS] IANA, ., "Autonomous System (AS) Numbers", July 2013, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Haas & Mitchell Expires January 16, 2014 [Page 3] Internet-Draft Last AS Reservation July 2013 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet Autonomous System (AS) Number Space", RFC 6793, December 2012. 8.2. Informative References [I-D.ietf-idr-as-private-reservation] Mitchell, J., "Autonomous System (AS) Reservation for Private Use", draft-ietf-idr-as-private-reservation-05 (work in progress), May 2013. [IANA.WK] IANA, ., "Border Gateway Protocol (BGP) Well-known Communities", July 2013, . [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, August 1996. Appendix A. Acknowledgements The authors would like to thank Michelle Cotton and Elwyn Davis for encouraging the proper documentation of the reservation of these ASNs. The authors would also like to thank David Farmer for his contributions to the document. Authors' Addresses Jeffrey Haas Juniper Networks Email: jhaas@juniper.net Jon Mitchell Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA Email: Jon.Mitchell@microsoft.com Haas & Mitchell Expires January 16, 2014 [Page 4]