Network Working Group                                        J. Mitchell
Internet-Draft                                     Microsoft Corporation
Updates: 1930 (if approved)                             February 7, 2013
Intended status: BCP
Expires: August 11, 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 MUST 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 by
   replacing Section 10.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on August 11, 2013.

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   the Trust Legal Provisions and are provided without warranty as
   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 datacenter 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 limited size of the current range of Private Use ASNs has led to
   the re-use of the same ASN 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
   [RFC6793], 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.  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 usage of the BGP protocol in
   networks that utilize Private Use ASNs, two ranges of ASNs are
   reserved by this document in Section 6.  The first which was

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   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 [RFC6793].

4.  Operational Considerations

   If Private Use ASNs are used and prefixes are originated from these
   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 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.  Some existing
   implementations that remove Private Use ASNs from the AS_PATH may
   fail to remove Private Use ASNs if the AS_PATH contains a mixture of
   Private Use and Non-Private Use ASNs.  If such 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 path,
   these implementations may cease to remove any Private Use ASNs from
   the AS_PATH.  Normal AS_PATH filtering may be used to prevent
   prefixes originating from Private Use ASNs from being advertised to
   the global Internet.  Using AS_PATH filtering to filter the new range
   of Private Use ASNs on a network may also mitigate the leaking of
   Private Use ASNs to the global Internet in certain cases.  These
   cases include the case where a network is reliant on AS_PATH
   manipulation features that have not been updated to recognize the new
   range as described above.

5.  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, Warren Kumari, and Jeff Wheeler
   for their comments and suggestions.

6.  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 94,967,295 (value to replace
   TBD1 below) is suggested corresponding to the range of 4200000000

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   (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].

7.  Security Considerations

   This document does not introduce any additional security concerns in
   regards to Private Use ASNs.

8.  References

8.1.  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.

8.2.  Informative References

   [IANA.AS]  IANA, "Autonomous System (AS) Numbers", February 2013,

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

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Author's Address

   Jon Mitchell
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA  98052


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