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Internet Engineering Task Force (IETF)                       J. MitchellRequest for Comments: 6996                         Microsoft CorporationBCP: 6                                                         July 2013Updates:1930Category: Best Current PracticeISSN: 2070-1721Autonomous System (AS) Reservation for Private UseAbstract   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 updatesRFC 1930 by   replacingSection 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6996.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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]

RFC 6996               Private Use AS Reservation              July 20131.  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 inSection 10 of [RFC1930].  Since the time that the range   was reserved, the Border Gateway Protocol (BGP) [RFC4271] 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" [RFC6793], 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 inRFC 2119 [RFC2119].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 bySection 5 of this document.  The first is part of the   original 16-bit Autonomous System range previously defined in   [RFC1930], and the second is a larger range out of the Four-Octet AS   Number Space [RFC6793].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 [RFC6793] 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 suchMitchell                  Best Current Practice                 [Page 2]

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 toSection 4.   General BGP security considerations are discussed in [RFC4271] and   [RFC4272].  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.  References7.1.  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.   [RFC6793]  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]

RFC 6996               Private Use AS Reservation              July 20137.2.  Informative References   [IANA.AS]  IANA, "Autonomous System (AS) Numbers",              <http://www.iana.org/assignments/as-numbers/>.   [RFC1930]  Hawkinson, J. and T. Bates, "Guidelines for creation,              selection, and registration of an Autonomous System (AS)",BCP 6,RFC 1930, March 1996.   [RFC4272]  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.comMitchell                  Best Current Practice                 [Page 4]