RFC 1518 (rfc1518) - Page 3 of 27
An Architecture for IP Address Allocation with CIDR
Alternative Format: Original Text Document
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