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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


   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

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.

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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 [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",
   document are to be interpreted as described in RFC 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 by Section 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 such

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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

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 [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.  References

7.1.  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.

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RFC 6996               Private Use AS Reservation              July 2013

7.2.  Informative References

   [IANA.AS]  IANA, "Autonomous System (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

   EMail: Jon.Mitchell@microsoft.com

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