Network Working Group                                        J. Mitchell
Internet-Draft                                     Microsoft Corporation
Updates: 1930 (if approved)                                June 20, 2012
Intended status: Informational
Expires: December 22, 2012

           Autonomous System (AS) Reservation for Private Use


   This document describes the reservation of Autonomous System numbers
   (ASNs) that may be used within networks but 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 December 22, 2012.

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   described in the Simplified BSD License.

1.  Introduction

   The original IANA reservation of ASNs for private use was a block of
   1023 ASNs.  This was documented by IETF in Section 10 of [RFC1930]
   that specified the private use ASN range as 64512 through 65535
   (implying the inclusion of ASN 65535).  Since that range was reserved
   and documented over a decade ago, BGP has seen much wider deployment
   in Service Provider, Enterprise and Content Provider networks.  The
   use cases in these networks for private use ASNs 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 for networks with requirements for multi-homing or
   provider redundancy.

   The limited size of the current range of private use ASNs has led to
   the usage 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 have been largely out of
   scope of 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 for reassignment in existing networks cannot be
   coordinated given these ASNs by definition are not registered.
   Therefore this document clarifies the existing ASN range, while
   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, reserved block available 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.  Prior to making use of the second, numerically
   higher, range of these ASNs network operators should be confident any
   implementation specific features or filters that recognize private
   use ASNs have been updated to recognize both ranges correctly so that
   no unintended announcement of private use ASNs to the Internet

4.  Acknowledgements

   The author would like to acknowledge Christopher Morrow and Jason
   Schiller for their advice on how to pursue this change.

5.  IANA Considerations

   [Note to IANA, not for publication: The IANA may wish to consider
   updating the existing private use AS number reservation to explicitly
   include ASN 65535 that has been documented in RFC 1930 as well as
   implemented in a number of implementations that recognize private use
   ASNs as part of the existing range.  Further, to maintain consistency
   from an operator standpoint, it is suggested that the end of the "32-
   bit number set" be reserved for Private Use, and a size of 967,295 is
   suggested corresponding to the range of 4294000000 to 4294967295
   inclusive, primarily motivated by being visibly recognizable while
   not consuming a large portion of the total ASN space.]

   [Note to WG, not for publication: a small poll of network
   implementors was taken and it was not felt optimizing the range to a
   bit boundary was important for control plane performance of any
   features that recognize private use ASNs - others implementors in WG
   may want to weigh in here.  Also very interested in feedback on
   appropriate sizing of the future range given the many current and
   future uses of BGP in networks]

   (If approved) IANA has reserved, for Private Use, a contiguous block
   of TBD (1023 or 1024) Autonomous System numbers from the "16-bit
   Autonomous System Numbers" registry, namely 64512 - TBD1 (65534 or
   65535) inclusive.

   (If approved) IANA has also reserved, for Private Use, a contiguous
   block of TBD Autonomous System numbers from the "32-bit Autonomous
   System Numbers" registry, namely TBD2 - TBD3 inclusive.

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   (If approved) These reservations have been documented in the IANA AS
   Number Registry [IANA.AS].

6.  Security Considerations

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

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", June 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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