RFC 1519 (rfc1519) - Page 3 of 24

Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy

RFC 1519                 CIDR Address Strategy            September 1993


   The proposed solution is to topologically allocate future IP address
   assignment, by allocating segments of the IP address space to the
   transit routing domains.

   This plan for allocating IP addresses should be undertaken as soon as
   possible.  We believe that this will suffice as a short term
   strategy, to fill the gap between now and the time when a viable long
   term plan can be put into place and deployed effectively.  This plan
   should be viable for at least three (3) years, after which time,
   deployment of a suitable long term solution is expected to occur.

   This plan is primarily directed at the first two problems listed
   above.  We believe that the judicious use of variable-length
   subnetting techniques should help defer the onset of the last problem
   problem, the exhaustion of the 32-bit address space. Note also that
   improved tools for performing address allocation in a "supernetted"
   and variably-subnetted world would greatly help the user community in
   accepting these sometimes confusing techniques. Efforts to create
   some simple tools for this purpose should be encouraged by the
   Internet community.

   Note that this plan neither requires nor assumes that already
   assigned addresses will be reassigned, though if doing so were
   possible, it would further reduce routing table sizes. It is assumed
   that routing technology will be capable of dealing with the current
   routing table size and with some reasonably small rate of growth.
   The emphasis of this plan is on significantly slowing the rate of
   this growth.

   Note that this plan does not require domains to renumber if they
   change their attached transit routing domain.  Domains are encouraged
   to renumber so that their individual address allocations do not need
   to be advertised.

   This plan will not affect the deployment of any specific long term
   plan, and therefore, this document will not discuss any long term
   plans for routing and address architectures.

2.  CIDR address allocation

   There are two basic components of this addressing and routing plan:
   one, to distribute the allocation of Internet address space and two,
   to provide a mechanism for the aggregation of routing information.

   2.1  Aggregation and its limitations

   One major goal of this addressing plan is to allocate Internet
   address space in such a manner as to allow aggregation of routing



Fuller, Li, Yu & Varadhan