1.  Problem, Goal, and Motivation

   As the Internet has evolved and grown over in recent years, it has
   become evident that it is soon to face several serious scaling
   problems. These include:

      1.   Exhaustion of the class B network address space. One
           fundamental cause of this problem is the lack of a network
           class of a size which is appropriate for mid-sized
           organization; class C, with a maximum of 254 host
           addresses, is too small, while class B, which allows up to
           65534 addresses, is too large for most organizations.

      2.   Growth of routing tables in Internet routers beyond the
           ability of current software, hardware, and people to
           effectively manage.

      3.   Eventual exhaustion of the 32-bit IP address space.

   It has become clear that the first two of these problems are likely
   to become critical within the next one to three years.  This memo
   attempts to deal with these problems by proposing a mechanism to slow
   the growth of the routing table and the need for allocating new IP
   network numbers. It does not attempt to solve the third problem,
   which is of a more long-term nature, but instead endeavors to ease
   enough of the short to mid-term difficulties to allow the Internet to
   continue to function efficiently while progress is made on a longer-
   term solution.




Fuller, Li, Yu & Varadhan                                       [Page 2]

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.