Reservation of Last Autonomous System (AS) Numbers
RFC 7300
Document | Type |
RFC - Best Current Practice
(July 2014; No errata)
Updates RFC 1930
|
|
---|---|---|---|
Authors | Jeffrey Haas , Jon Mitchell | ||
Last updated | 2015-10-14 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Susan Hares | ||
Shepherd write-up | Show (last changed 2014-03-14) | ||
IESG | IESG state | RFC 7300 (Best Current Practice) | |
Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Alia Atlas | ||
Send notices to | (None) | ||
IANA | IANA review state | IANA OK - Actions Needed | |
IANA action state | RFC-Ed-Ack |
Internet Engineering Task Force (IETF) J. Haas Request for Comments: 7300 Juniper Networks BCP: 6 J. Mitchell Updates: 1930 Microsoft Corporation Category: Best Current Practice July 2014 ISSN: 2070-1721 Reservation of Last Autonomous System (AS) Numbers 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. This document updates Section 10 of RFC 1930. Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs 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/rfc7300. Copyright Notice Copyright (c) 2014 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 Best Current Practice [Page 1] RFC 7300 Last AS Reservation July 2014 1. Introduction Over a decade ago, IANA reserved the last Autonomous System Number (ASN) of the 16-bit ASN range, 65535, with the intention that it not be used by network operators running BGP [RFC4271]. Since the introduction of "BGP Support for Four-Octet Autonomous System (AS) Number Space" [RFC6793], IANA has also reserved the last ASN of the 32-bit autonomous system number range, 4294967295. This reservation has been documented in the IANA "Autonomous System (AS) Numbers" registry [IANA.AS]. Although these "Last ASNs" border on Private Use ASN [RFC6996] ranges, they are not defined or reserved as Private Use ASNs by [IANA.AS]. This document describes the reasoning for reserving 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 Reservation of the Last ASNs A subset of the BGP communities of ASN 65535, the last ASN of the 16-bit range, are reserved for use by Well-known Communities as described in [RFC1997] and [IANA.WK]. Although this is not currently true of ASN 4294967295, if there is a future need for another Special Use ASN that is not designed to be globally routable, or for the associated BGP communities of such an ASN, ASN 4294967295 could be a valid candidate for such purpose. This document does not prescribe any such Special Use to this ASN at the time of publication. 4. Operational Considerations Operators SHOULD NOT use these Last ASNs for any other purpose or as Private Use ASNs. Operational use of these Last ASNs could have 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 undesirable routing behavior. Last ASNs MUST NOT be advertised to the global Internet within AS_PATH or AS4_PATH attributes. Operators SHOULD filter Last ASNs within the AS_PATH and AS4_PATH attributes. Haas & Mitchell Best Current Practice [Page 2] RFC 7300 Last AS Reservation July 2014 5. Implementation Considerations While Last ASNs are reserved, they remain valid ASNs from a BGP perspective. Therefore, implementations of BGP [RFC4271] SHOULD NOT treat the use of Last ASNs as any type of protocol error. However, if a Last ASN is configured as the local AS, implementations MAY generate a warning message indicating 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 Last ASNs. 6. IANA ConsiderationsShow full document text