RFC 1518 (rfc1518) - Page 2 of 27

An Architecture for IP Address Allocation with CIDR

RFC 1518          CIDR Address Allocation Architecture    September 1993


   There are two aspects of interest when discussing IP address
   allocation within the Internet. The first is the set of
   administrative requirements for obtaining and allocating IP
   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.

   The architecture and recommendations provided in this paper are
   intended for immediate deployment. This paper specifically does not
   address long-term research issues, such as complex policy-based
   routing requirements.

   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 IP address allocation in
   the Internet. Topics covered include:

      - Benefits of encoding some topological information in IP
        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 IP
        addressing and routing components;

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

      - Allocation of the IP addresses by the Internet Registry;

      - Choice of the high-order portion of the IP 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 IP address allocation,
   both technical and administrative, that are not covered in this
   paper.  Topics not covered or mentioned only superficially include:



Rekhter & Li