An Architecture for IPv6 Unicast Address Allocation
RFC 1887

Document Type RFC - Informational (December 1995; No errata)
Last updated 2013-03-02
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Network Working Group                                        Y. Rekhter
Request for Comments: 1887                                cisco Systems
Category: Informational                                           T. Li
                                                          cisco Systems
                                                          December 1995

          An Architecture for IPv6 Unicast Address Allocation

Status of this Memo

   This document provides information for the Internet community.  This
   memo does not specify an Internet standard of any kind.  Distribution
   of this memo is unlimited.


   This document provides an architecture for allocating IPv6 [1]
   unicast addresses in the Internet. The overall IPv6 addressing
   architecture is defined in [2].  This document does not go into the
   details of an addressing plan.

1.   Scope

   The global internet can be modeled as a collection of hosts
   interconnected via transmission and switching facilities.  Control
   over the collection of hosts and the transmission and switching
   facilities that compose the networking resources of the global
   internet is not homogeneous, but is distributed among multiple
   administrative authorities. Resources under control of a single
   administration within a contiguous segment of network topology form a
   domain.  For the rest of this paper, `domain' and `routing domain'
   will be used interchangeably.

   Domains that share their resources with other domains are called
   network service providers (or just providers). Domains that utilize
   other domain's resources are called network service subscribers (or
   just subscribers).  A given domain may act as a provider and a
   subscriber simultaneously.

Rekhter & Li                 Informational                      [Page 1]
RFC 1887      IPv6 Unicast Address Allocation Architecture December 1995

   There are two aspects of interest when discussing IPv6 unicast
   address allocation within the Internet. The first is the set of
   administrative requirements for obtaining and allocating IPv6
   addresses; the second is the technical aspect of such assignments,
   having largely to do with routing, both within a routing domain
   (intra-domain routing) and between routing domains (inter-domain
   routing). This paper focuses on the technical issues.

   In the current Internet many routing domains (such as corporate and
   campus networks) attach to transit networks (such as regionals) in
   only one or a small number of carefully controlled access points.
   The former act as subscribers, while the latter act as providers.

   Addressing solutions which require substantial changes or constraints
   on the current topology are not considered.

   The architecture and recommendations in this paper are oriented
   primarily toward the large-scale division of IPv6 address allocation
   in the Internet.  Topics covered include:

      - Benefits of encoding some topological information in IPv6
        addresses to significantly reduce routing protocol overhead;

      - The anticipated need for additional levels of hierarchy in
        Internet addressing to support network growth;

      - The recommended mapping between Internet topological entities
        (i.e., service providers, and service subscribers) and IPv6
        addressing and routing components;

      - The recommended division of IPv6 address assignment among
        service providers (e.g., backbones, regionals), and service
        subscribers (e.g., sites);

      - Allocation of the IPv6 addresses by the Internet Registry;

      - Choice of the high-order portion of the IPv6 addresses in leaf
        routing domains that are connected to more than one service
        provider (e.g., backbone or a regional network).

   It is noted that there are other aspects of IPv6 address allocation,
   both technical and administrative, that are not covered in this
   paper.  Topics not covered or mentioned only superficially include:

      - A specific plan for address assignment;

      - Embedding address spaces from other network layer protocols
        (including IPv4) in the IPv6 address space and the addressing

Rekhter & Li                 Informational                      [Page 2]
RFC 1887      IPv6 Unicast Address Allocation Architecture December 1995

        architecture for such embedded addresses;

      - Multicast addressing;

      - Address allocation for mobile hosts;

      - Identification of specific administrative domains in the

      - Policy or mechanisms for making registered information known to
        third parties (such as the entity to which a specific IPv6
        address or a potion of the IPv6 address space has been

      - How a routing domain (especially a site) should organize its
        internal topology or allocate portions of its IPv6 address
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