An IPv6 Provider-Based Unicast Address Format
RFC 2073

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Network Working Group                                         Y. Rekhter
Request for Comments: 2073                                         cisco
Category: Standards Track                                    P. Lothberg
                                                                STUPI.AB
                                                               R. Hinden
                                                        Ipsilon Networks
                                                              S. Deering
                                                              Xerox PARC
                                                               J. Postel
                                                                     ISI
                                                                 Editors
                                                            January 1997

             An IPv6 Provider-Based 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.

1.0 Introduction

   This document defines an IPv6 provider-based unicast address format
   for use in the Internet.  The address format defined in this document
   is consistent with the "IPv6 Addressing Architecture" [ARCH] and the
   "An Architecture for IPv6 Unicast Address Allocation" [ALLOC], and is
   intended to facilitate scalable Internet routing.

   The unicast address format defined in this document doesn't preclude
   the use of other unicast address formats.

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 "subscriber".  When this name is used with the term "ID" (for
   "identifier") after the name (e.g., "subscriber ID"), it refers to
   the contents of the named field.  When it is used with the term
   "prefix" (e.g., "subscriber prefix") it refers to all of the address
   up to and including this field.

Rekhter, et. al.            Standards Track                     [Page 1]
RFC 2073       IPv6 Provider-Based Unicast Address Format   January 1997

   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 010 (binary) Format
   Prefix for Provider-Based 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 "010" Format
   Prefix is defined here.

3.0 IPv6 Provider-Based Unicast Address Format

   This document defines an address format for the IPv6 provider-based
   unicast address assignment.  It is expected that this address format
   will be widely used for IPv6 nodes connected to the Internet.

   The address format defined in this document conforms to the
   "Architecture for IPv6 Unicast Address Allocation" [ALLOC].
   Specifically, the format is designed to support aggregation of
   network layer reachability information at multiple levels of routing
   hierarchy.

   For addresses of the format described in this document the address
   administration is organized into a three level hierarchy -- registry,
   provider, and subscriber.  The address format defined here allows
   flexible address allocation at each level of the address
   administration hierarchy in such a way as to support a wide spectrum
   of demands for address allocation.

   This document assumes that the Internet routing system doesn't make
   any assumptions about the specific structure and semantics of an IPv6
   address, except for the structure and semantics of the Format Prefix
   part of the address, and the use of the "longest prefix match"
   algorithm (on arbitrary bit boundaries) for making a forwarding
   decision.

   The address format defined in this document is intended to facilitate
   scalable Internet-wide routing that does not impose any constraints
   on connectivity among the providers, as well as among the providers
   and subscribers.

Rekhter, et. al.            Standards Track                     [Page 2]
RFC 2073       IPv6 Provider-Based Unicast Address Format   January 1997

3.1 Provider-Based Unicast Address Structure

   For the purpose of address allocation, the address format defined in
   this document consists of the following parts:  Format Prefix,
   Registry ID, Provider ID, Subscriber ID, and an Intra-Subscriber