IPv6 Global Unicast Address Format
draft-ietf-ipv6-unicast-aggr-v2-02

INTERNET-DRAFT                                         R. Hinden, Nokia
February 26, 2003                                     S. Deering, Cisco
                                                       E. Nordmark, Sun

                   IPv6 Global Unicast Address Format

                <draft-ietf-ipv6-unicast-aggr-v2-02.txt>

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

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   The list of Internet-Draft Shadow Directories can be accessed at
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   This internet draft expires on August 26, 2003.

Abstract

   RFC2374 "An IPv6 Aggregatable Global Unicast Address Format" defined
   an IPv6 address allocation structure that includes TLA (Top Level
   Aggregator) and NLA (Next Level Aggregator).  This document replaces
   RFC2374, and makes RFC 2374 and the TLA/NLA structure historic.

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1.0 Introduction

   RFC2374 "An IPv6 Aggregatable Global Unicast Address Format" defined
   an IPv6 address allocation structure that includes TLA (Top Level
   Aggregator) and NLA (Next Level Aggregator).  This document replaces
   RFC2374, and makes RFC 2374 and the TLA/NLA structure historic.

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   The TLA/NLA scheme has been replaced by a coordinated allocation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

   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.

   RFC2374 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, since the IANA might later be directed to delegate currently
   unassigned parts of the IPv6 address space to the purpose of Global
   Unicast as well.

   The SLA (subnet local aggregator) field in RFC2374 remains in
   function but with a different name in [ARCH].  Its new name is
   "subnet ID".

   This documented replaces RFC2374, "An IPv6 Aggregatable Global
   Unicast Address Format".  RFC2374 will become historic.

3.0 Address Format

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

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      |         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].

   [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         |
      +-------------------------+-----------+----------------------------+

   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 in 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 RFC3177 is:

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

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4.0 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.

5.0 References

   Normative

   [ARCH]    Hinden, R., "IP Version 6 Addressing Architecture",
             Internet Draft, <draft-ietf-ipngwg-addr-arch-v3-11.txt>,
             October 2002.

   [IPV6]    Deering, S., R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", RFC2460, December 1998.

   Non-Normative

   [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" RFC3177, September 2001.

6.0 Security Considerations

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

7.0 Authors' Addresses

   Robert M. Hinden                  email: bob.hinden@nokia.com
   Nokia
   313 Fairchild Drive
   Mountain View, CA
   US

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   Stephen E. Deering                email: deering@cisco.com
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134-1706
   US

   Erik Nordmark                     email: erik.nordmark@sun.com
   Sun Microsystems Laboratories
   180, avenue de l'Europe
   38334 SAINT ISMIER Cedex
   France

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