





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   The TLA/NLA scheme has been replaced by a coordinated allocation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.



Hinden, et al.               Informational                      [Page 1]

RFC 3587           IPv6 Global Unicast Address Format        August 2003


   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         |
    +-------------------------+-----------+----------------------------+








Hinden, et al.               Informational                      [Page 2]

RFC 3587           IPv6 Global Unicast Address Format        August 2003


   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.






Hinden, et al.               Informational                      [Page 3]

RFC 3587           IPv6 Global Unicast Address Format        August 2003


7.  Authors' Addresses

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

   EMail: bob.hinden@nokia.com


   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: erik.nordmark@sun.com


























Hinden, et al.               Informational                      [Page 4]

RFC 3587           IPv6 Global Unicast Address Format        August 2003


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.



















Hinden, et al.               Informational                      [Page 5]

