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/rfc6996.

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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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",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  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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  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 [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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7.2.  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: [email protected]






















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