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Network Working Group                                          R. HindenRequest for Comments: 3587                                         NokiaObsoletes:2374                                               S. DeeringCategory: Informational                                            Cisco                                                             E. Nordmark                                                                     Sun                                                             August 2003IPv6 Global Unicast Address FormatStatus 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 obsoletesRFC 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 makesRFC 2374 and the TLA/NLA   structure historic.1.  IntroductionRFC 2374, "An IPv6 Aggregatable Global Unicast Address Format",   defined an IPv6 address allocation structure that includes TLA and   NLA.  This document replacesRFC 2374, and makesRFC 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  TLA/NLA Made Historic   The TLA/NLA scheme has been replaced by a coordinated allocation   policy defined by the Regional Internet Registries (RIRs) [IPV6RIR].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 inRFC 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 inRFC 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.  References5.1.  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 20037.  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.comHinden, et al.               Informational                      [Page 4]

RFC 3587           IPv6 Global Unicast Address Format        August 20038.  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]