Network Working Group                                          R. Hinden
Request for Comments: 3587                                         Nokia
Obsoletes: 2374                                               S. Deering
Category: Informational                                            Cisco
                                                            E. Nordmark
                                                                    Sun
                                                            August 2003


                  IPv6 Global Unicast Address Format

Status of this Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

  This document obsoletes RFC 2374, "An IPv6 Aggregatable Global
  Unicast Address Format".  It defined an IPv6 address allocation
  structure that includes Top Level Aggregator (TLA) and Next Level
  Aggregator (NLA).  This document makes RFC 2374 and the TLA/NLA
  structure historic.

1.  Introduction

  RFC 2374, "An IPv6 Aggregatable Global Unicast Address Format",
  defined an IPv6 address allocation structure that includes TLA and
  NLA.  This document replaces RFC 2374, and makes RFC 2374 and the
  TLA/NLA structure historic.

2.  TLA/NLA Made Historic

  The TLA/NLA scheme has been replaced by a coordinated allocation
  policy defined by the Regional Internet Registries (RIRs) [IPV6RIR].

  Part of the motivation for obsoleting the TLA/NLA structure is
  technical; for instance, there is concern that TLA/NLA is not the
  technically best approach at this stage of the deployment of IPv6.
  Moreover, the allocation of IPv6 addresses is related to policy and
  to the stewardship of the IP address space and routing table size,
  which the RIRs have been managing for IPv4.  It is likely that the
  RIRs' policy will evolve as IPv6 deployment proceeds.



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  The IETF has provided technical input to the RIRs (for example,
  [RFC3177]), which the RIRs have taken into account when defining
  their address allocation policy.

  RFC 2374 was the definition of addresses for Format Prefix 001
  (2000::/3) which is formally made historic by this document.  Even
  though currently only 2000::/3 is being delegated by the IANA,
  implementations should not make any assumptions about 2000::/3 being
  special.  In the future, the IANA might be directed to delegate
  currently unassigned portions of the IPv6 address space for the
  purpose of Global Unicast as well.

  The Subnet Local Aggregator (SLA) field in RFC 2374 remains in
  function but with a different name in [ARCH].  Its new name is
  "subnet ID".

3.  Address Format

  The general format for IPv6 global unicast addresses as defined in
  "IP Version 6 Addressing Architecture" [ARCH] is as follows:

   |         n bits          |   m bits  |       128-n-m bits         |
   +-------------------------+-----------+----------------------------+
   | global routing prefix   | subnet ID |       interface ID         |
   +-------------------------+-----------+----------------------------+

  where the global routing prefix is a (typically
  hierarchically-structured) value assigned to a site (a cluster of
  subnets/links), the subnet ID is an identifier of a subnet within the
  site, and the interface ID is as defined in section 2.5.1 of [ARCH].
  The global routing prefix is designed to be structured hierarchically
  by the RIRs and ISPs.  The subnet field is designed to be structured
  hierarchically by site administrators.

  [ARCH] also requires that all unicast addresses, except those that
  start with binary value 000, have Interface IDs that are 64 bits long
  and to be constructed in Modified EUI-64 format.  The format of
  global unicast address in this case is:

   |         n bits          | 64-n bits |       64 bits              |
   +-------------------------+-----------+----------------------------+
   | global routing prefix   | subnet ID |       interface ID         |
   +-------------------------+-----------+----------------------------+








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  where the routing prefix is a value assigned to identify a site (a
  cluster of subnets/links), the subnet ID is an identifier of a subnet
  within the site, and the interface ID is a modified EUI-64 format as
  defined in [ARCH].

  An example of the resulting format of global unicast address under
  the 2000::/3 prefix that is currently being delegated by the IANA and
  consistent with the recommendations in RFC 3177 is:

   | 3 |     45 bits         |  16 bits  |       64 bits              |
   +---+---------------------+-----------+----------------------------+
   |001|global routing prefix| subnet ID |       interface ID         |
   +---+---------------------+-----------+----------------------------+

4.  Acknowledgments

  The authors would like to express our thanks to Alain Durand, Brian
  Carpenter, Fred Templin, Julian Sellers, Jun-ichiro Itojun Hagino,
  Margaret Wasserman, Michel Py, Pekka Savola, Tatuya Jinmei, and
  Thomas Narten for their review and constructive comments.

5.  References

5.1.  Normative References

  [ARCH]    Hinden, R. and S. Deering, "IP Version 6 Addressing
            Architecture", RFC 3513, April 2003.

  [IPV6]    Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, December 1998.

5.2.  Informative References

  [IPV6RIR] APNIC, ARIN, RIPE NCC, "IPv6 Address Allocation and
            Assignment Policy", Document ID: ripe-267,
            http://www.ripe.net/ripe/docs/ipv6policy.html, January 22,
            2003.

  [RFC3177] IAB/IESG, "Recommendations on IPv6 Address Allocations to
            Sites", RFC 3177, September 2001.

6.  Security Considerations

  IPv6 addressing documents do not have any direct impact on Internet
  infrastructure security.






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7.  Authors' Addresses

  Robert M. Hinden
  Nokia
  313 Fairchild Drive
  Mountain View, CA
  USA

  EMail: [email protected]


  Stephen E. Deering
  Cisco Systems, Inc.
  170 West Tasman Drive
  San Jose, CA 95134-1706
  USA


  Erik Nordmark
  Sun Microsystems Laboratories
  180, avenue de l'Europe
  38334 SAINT ISMIER Cedex
  France

  EMail: [email protected]


























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8.  Full Copyright Statement

  Copyright (C) The Internet Society (2003).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assignees.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.



















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