An IPv6 Aggregatable Global Unicast Address Format
RFC 2374

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Network Working Group                                        R. Hinden
Request for Comments: 2374                                       Nokia
Obsoletes: 2073                                              M. O'Dell
Category: Standards Track                                        UUNET
                                                            S. Deering
                                                                 Cisco
                                                             July 1998

           An IPv6 Aggregatable Global Unicast Address Format

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

1.0 Introduction

   This document defines an IPv6 aggregatable global unicast address
   format for use in the Internet.  The address format defined in this
   document is consistent with the IPv6 Protocol [IPV6] and the "IPv6
   Addressing Architecture" [ARCH].  It is designed to facilitate
   scalable Internet routing.

   This documented replaces RFC 2073, "An IPv6 Provider-Based Unicast
   Address Format".  RFC 2073 will become historic.  The Aggregatable
   Global Unicast Address Format is an improvement over RFC 2073 in a
   number of areas.  The major changes include removal of the registry
   bits because they are not needed for route aggregation, support of
   EUI-64 based interface identifiers, support of provider and exchange
   based aggregation, separation of public and site topology, and new
   aggregation based terminology.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC 2119].

Hinden, et. al.             Standards Track                     [Page 1]
RFC 2374           IPv6 Global Unicast Address Format          July 1998

2.0 Overview of the IPv6 Address

   IPv6 addresses are 128-bit identifiers for interfaces and sets of
   interfaces.  There are three types of addresses: Unicast, Anycast,
   and Multicast.  This document defines a specific type of Unicast
   address.

   In this document, fields in addresses are given specific names, for
   example "subnet".  When this name is used with the term "ID" (for
   "identifier") after the name (e.g., "subnet ID"), it refers to the
   contents of the named field.  When it is used with the term "prefix"
   (e.g.  "subnet prefix") it refers to all of the addressing bits to
   the left of and including this field.

   IPv6 unicast addresses are designed assuming that the Internet
   routing system makes forwarding decisions based on a "longest prefix
   match" algorithm on arbitrary bit boundaries and does not have any
   knowledge of the internal structure of IPv6 addresses.  The structure
   in IPv6 addresses is for assignment and allocation.  The only
   exception to this is the distinction made between unicast and
   multicast addresses.

   The specific type of an IPv6 address is indicated by the leading bits
   in the address.  The variable-length field comprising these leading
   bits is called the Format Prefix (FP).

   This document defines an address format for the 001 (binary) Format
   Prefix for Aggregatable Global Unicast addresses. The same address
   format could be used for other Format Prefixes, as long as these
   Format Prefixes also identify IPv6 unicast addresses.  Only the "001"
   Format Prefix is defined here.

3.0 IPv6 Aggregatable Global Unicast Address Format

   This document defines an address format for the IPv6 aggregatable
   global unicast address assignment.  The authors believe that this
   address format will be widely used for IPv6 nodes connected to the
   Internet.  This address format is designed to support both the
   current provider-based aggregation and a new type of exchange-based
   aggregation.  The combination will allow efficient routing
   aggregation for sites that connect directly to providers and for
   sites that connect to exchanges.  Sites will have the choice to
   connect to either type of aggregation entity.

Hinden, et. al.             Standards Track                     [Page 2]
RFC 2374           IPv6 Global Unicast Address Format          July 1998

   While this address format is designed to support exchange-based
   aggregation (in addition to current provider-based aggregation) it is
   not dependent on exchanges for it's overall route aggregation
   properties.  It will provide efficient route aggregation with only
   provider-based aggregation.

   Aggregatable addresses are organized into a three level hierarchy: