RFC 1518 (rfc1518) - Page 3 of 27

An Architecture for IP Address Allocation with CIDR

RFC 1518          CIDR Address Allocation Architecture    September 1993


      - Identification of specific administrative domains in the
        Internet;

      - Policy or mechanisms for making registered information known to
        third parties (such as the entity to which a specific IP address
        or a portion of the IP address space has been allocated);

      - How a routing domain (especially a site) should organize its
        internal topology or allocate portions of its IP address space;
        the relationship between topology and addresses is discussed,
        but the method of deciding on a particular topology or internal
        addressing plan is not; and,

       - Procedures for assigning host IP addresses.

3.  Background

   Some background information is provided in this section that is
   helpful in understanding the issues involved in IP address
   allocation. A brief discussion of IP routing is provided.

   IP partitions the routing problem into three parts:

      - routing exchanges between end systems and routers (ARP),

      - routing exchanges between routers in the same routing domain
        (interior routing), and,

      - routing among routing domains (exterior routing).

4. IP Addresses and Routing

   For the purposes of this paper, an IP prefix is an IP address and
   some indication of the leftmost contiguous significant bits within
   this address. Throughout this paper IP address prefixes will be
   expressed as  tuples, such that a bitwise logical
   AND operation on the IP-address and IP-mask components of a tuple
   yields the sequence of leftmost contiguous significant bits that form
   the IP address prefix. For example a tuple with the value  denotes an IP address prefix with 16 leftmost contiguous
   significant bits.

   When determining an administrative policy for IP address assignment,
   it is important to understand the technical consequences. The
   objective behind the use of hierarchical routing is to achieve some
   level of routing data abstraction, or summarization, to reduce the
   cpu, memory, and transmission bandwidth consumed in support of
   routing.



Rekhter & Li