RFC 2073 (rfc2073) - Page 3 of 7

An IPv6 Provider-Based Unicast Address Format

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
   part.  The Intra-Subscriber part definition is the responsibility of
   the subscriber and is not defined in this document.  The provider-
   based unicast address format is as follows:

      | 3 |  5 bits  |   n bits   |   56-n bits  |        64 bits     |
      +---+----------+------------+--------------+--------------------+
      |010|RegistryID| ProviderID | SubscriberID |  Intra-Subscriber  |
      +---+----------+------------+--------------+--------------------+

   The following sections specify each part of the IPv6 Provider-Based
   Unicast address format.  In general other allocation strategies are
   possible within this framework, but the ones described in this
   document will be used to assign IPv6 provider-based addresses.

   3.2 Registry ID

   With the growth of the Internet and its increasing globalization,
   much thought has been given to the evolution of the Network Layer
   address space allocation and assignment process.  RFC 1466,
   "Guidelines for Management of IP Address Space", proposes a plan that
   defines distributed allocation and assignment of the IPv4 address
   space.

   As the Internet transitions to IPv6, the plan for distributed
   allocation and assignment of the IPv4 address space established in
   RFC 1466 forms a base for the distributed allocation and assignment of
   the IPv6 address space.

   The Internet Assigned Number Authority (IANA) is the principal
   registry for the IPv6 address space.  The IANA may allocate blocks of
   IPv6 addresses and delegate the assignment of those blocks to
   qualified Regional Registries.  The IANA will serve as the default
   registry in cases where no delegated registration authority has been
   identified.

   The Registry ID of the IPv6 provider-based unicast address format is
   intended to facilitate a broad geographic address allocation and
   facilitate the operations of the distributed Regional Registries.

   The Registry ID immediately follows the format prefix part of an IPv6
   address.





Rekhter, et. al.            Standards Track