Network Working Group                                        J. Mitchell
Internet-Draft                                     Microsoft Corporation
Updates: 1930 (if approved)                               August 6, 2012
Intended status: Informational
Expires: February 7, 2013

           Autonomous System (AS) Reservation for Private Use


   This document describes the reservation of Autonomous System numbers
   (ASNs) that are for private use only and should not be advertised to
   the Internet, known as private use ASNs.  This document enlarges the
   total space available for private use ASNs by documenting the
   reservation of a second, larger range and updates RFC 1930.

Status of this Memo

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   This Internet-Draft will expire on February 7, 2013.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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
   IETF in Section 10 of [RFC1930].  Since the time when that range was
   reserved, BGP has seen much wider deployment in service provider,
   enterprise and content provider networks.  The places in these
   networks where private use ASNs are in use include networks that are
   attached to the Internet, utilizing implementation specific features
   to remove them upon advertisement to Internet peers, and networks
   that are not attached to the Internet.  The displacement of Frame
   Relay and ATM based VPNs by BGP/MPLS IP VPNs [RFC4364] has also
   increased the deployment of BGP to a larger number of sites,
   especially in networks with requirements for multi-homing or provider

   The limited size of the current range of private use ASNs has led to
   the re-use of private use ASNs within a single organization,
   requiring the use of a number of implementation specific features
   that manipulate the AS_PATH or remove AS_PATH based loop prevention
   described in Section 9 of [RFC4271].  These workarounds have
   increased the operational complexity of the networks since the
   implementations of these functions vary and are not defined in
   existing BGP standards.

   Since the introduction of BGP Support for Four-octet AS Number Space
   [RFC4893], the total size of the ASN space has increased
   dramatically, and a larger subset of the space should be available to
   network operators to deploy in 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 these
   ASNs by definition are not registered.  Therefore this documents the
   existing private use ASN reservation, while also introducing a
   second, larger range that can also be utilized.

2.  Private Use ASNs

   To allow the continued growth of usage of the BGP protocol in
   networks that utilize private ASNs, two ranges of ASNs are reserved
   by this document in Section 5.  The first which was previously
   defined in [RFC1930] out of the original 16-bit Autonomous System
   range and a second, larger range out of the higher part of the Four-
   Octet AS Number Space [RFC4893].

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3.  Operational Considerations

   If private use ASNs are used and prefixes are originated from these
   private use ASNs which are destined to the Internet, private use ASNs
   must be removed from the AS_PATH before being advertised to the
   global Internet.  Operators are cautioned to ensure any filters or
   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.

4.  Acknowledgements

   The author would like to acknowledge Christopher Morrow and Jason
   Schiller for their advice on how to pursue this change.  The author
   also thanks Brian Dickson, David Farmer, and Jeffrey Haas for their
   comments and suggestions.

5.  IANA Considerations

   [Note to IANA, NOT for publication: The IANA should update the "16-
   bit Autonomous System Numbers" registry to reference this RFC (when
   published) for the existing private use reservation.  Further, to
   maintain consistency from an operator standpoint, it is suggested
   that the end of the "32-bit Autonomous System Numbers" range be
   reserved for Private Use, and a size of 16777215 (value to replace
   TBD1 below) is suggested corresponding to the range of 4278190080
   (value to replace TBD2 below) to 4294967294 (value to replace TBD3

   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 TBD1
   Autonomous System numbers from the "32-bit Autonomous System Numbers"
   registry, namely TBD2 - TBD3 inclusive.

   These reservations have been documented in the IANA Autonomous System
   Numbers Registry [IANA.AS].

6.  Security Considerations

   This document does not introduce any additional security concerns in
   regards to private use ASNs.

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7.  References

7.1.  Normative References

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.

7.2.  Informative References

   [IANA.AS]  IANA, "Autonomous System (AS) Numbers", August 2012,

   [RFC1930]  Hawkinson, J. and T. Bates, "Guidelines for creation,
              selection, and registration of an Autonomous System (AS)",
              BCP 6, RFC 1930, March 1996.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

Author's Address

   Jon Mitchell
   Microsoft Corporation
   12012 Sunset Hills Road
   Reston, VA  20190


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