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IETF RFC 6996



Last modified on Monday, July 29th, 2013

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Internet Engineering Task Force (IETF)                       J. Mitchell
Request for Comments: 6996                         Microsoft Corporation
BCP: 6                                                         July 2013
Updates: 1930
Category: Best Current Practice 
ISSN: 2070-1721


           Autonomous System (AS) Reservation for Private Use

 Abstract

   This document describes the reservation of Autonomous System Numbers
   (ASNs) that are for Private Use only, known as Private Use ASNs, and
   provides operational guidance on their use.  This document enlarges
   the total space available for Private Use ASNs by documenting the
   reservation of a second, larger range and updates RFC 1930 by
   replacing Section 10 of that document.

 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 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
   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/RFC 6996.

 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.




Mitchell                  Best Current Practice              PAGE 1 top


RFC 6996 Private Use AS Reservation July 2013 1. Introduction The original IANA reservation of Autonomous System Numbers (ASNs) for Private Use was a block of 1023 ASNs. This was also documented by the IETF in Section 10 of [RFC 1930]. Since the time that the range was reserved, the Border Gateway Protocol (BGP) [RFC 4271] has seen deployment in new application domains, such as data center networks, which require a larger Private Use AS space. Since the introduction of "BGP Support for Four-Octet Autonomous System (AS) Number Space" [RFC 6793], the total size of ASN space has increased dramatically. A larger subset of the space is available to network operators to deploy in these Private Use cases. The existing range of Private Use ASNs is widely deployed, and the ability to renumber this resource in existing networks cannot be coordinated given that these ASNs, by definition, are not registered. Therefore, this RFC documents the existing Private Use ASN reservation while also introducing a second, larger range that can also be utilized. 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 [RFC 2119]. 3. Private Use ASNs To allow the continued growth of BGP protocol usage in new network applications that utilize Private Use ASNs, two ranges of ASNs are reserved by Section 5 of this document. The first is part of the original 16-bit Autonomous System range previously defined in [RFC 1930], and the second is a larger range out of the Four-Octet AS Number Space [RFC 6793]. 4. Operational Considerations If Private Use ASNs are used and prefixes originate from these ASNs, Private Use ASNs MUST be removed from AS path attributes (including AS4_PATH if utilizing a four-octet AS number space) before being advertised to the global Internet. Operators SHOULD ensure that all External Border Gateway Protocol (EBGP) speakers support the extensions described in [RFC 6793] and that implementation-specific features that recognize Private Use ASNs have been updated to recognize both ranges prior to making use of the newer, numerically higher range of Private Use ASNs in the four-octet AS number space. Some existing implementations that remove Private Use ASNs from the AS_PATH are known to not remove Private Use ASNs if the AS_PATH contains a mixture of Private Use and Non-Private Use ASNs. If such Mitchell Best Current Practice PAGE 2 top

RFC 6996 Private Use AS Reservation July 2013 implementations have not been updated to recognize the new range of ASNs in this document and a mix of old and new range Private Use ASNs exist in the AS4_PATH, these implementations will likely cease to remove any Private Use ASNs from either of the AS path attributes. Normal AS path filtering MAY also be used to prevent prefixes originating from Private Use ASNs from being advertised to the global Internet. 5. IANA Considerations IANA has reserved, for Private Use, a contiguous block of 1023 Autonomous System numbers from the "16-bit Autonomous System Numbers" registry, namely 64512 - 65534 inclusive. IANA has also reserved, for Private Use, a contiguous block of 94,967,295 Autonomous System numbers from the "32-bit Autonomous System Numbers" registry, namely 4200000000 - 4294967294 inclusive. These reservations have been documented in the IANA "Autonomous System (AS) Numbers" registry [IANA.AS]. 6. Security Considerations Private Use ASNs do not raise any unique security concerns. Loss of connectivity might result from their inappropriate use, specifically outside of a single organization, since they are not globally unique. This loss of connectivity is limited to the organization using Private Use ASNs inappropriately or without reference to Section 4. General BGP security considerations are discussed in [RFC 4271] and [RFC 4272]. Identification of the originator of a route with a Private Use ASN in the AS path would have to be done by tracking the route back to the neighboring globally unique AS in the path or by inspecting other attributes. 7. References 7.1. Normative References [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC 4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC 6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet Autonomous System (AS) Number Space", RFC 6793, December 2012. Mitchell Best Current Practice PAGE 3 top

RFC 6996 Private Use AS Reservation July 2013 7.2. Informative References [IANA.AS] IANA, "Autonomous System (AS) Numbers", <http://www.iana.org/assignments/as-numbers/>. [RFC 1930] Hawkinson, J. and T. Bates, "Guidelines for creation, selection, and registration of an Autonomous System (AS)", BCP 6, RFC 1930, March 1996. [RFC 4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC 4272, January 2006. 8. Acknowledgements The author would like to acknowledge Christopher Morrow, Jason Schiller, and John Scudder for their advice on how to pursue this change. The author would also like to thank Brian Dickson, David Farmer, Jeffrey Haas, Nick Hilliard, Joel Jaeggli, Warren Kumari, and Jeff Wheeler for their comments and suggestions. Author's Address Jon Mitchell Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA EMail: Jon.Mitchell@microsoft.com Mitchell Best Current Practice PAGE 4 top

RFC TOTAL SIZE: 8198 bytes PUBLICATION DATE: Monday, July 29th, 2013 LEGAL RIGHTS: The IETF Trust (see BCP 78)


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