IPv6 Global Unicast Address Format
RFC 3587

 
Document Type RFC - Informational (August 2003; No errata)
Obsoletes RFC 2374
Last updated 2013-03-02
Stream IETF
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Stream WG state (None)
Consensus Unknown
Document shepherd No shepherd assigned
IESG IESG state RFC 3587 (Informational)
Telechat date
Responsible AD Thomas Narten
IESG note appears.
Send notices to <bob.hinden@nokia.com>, <mrw@windriver.com>
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   The TLA/NLA scheme has been replaced by a coordinated allocation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
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