Supernetting: an Address Assignment and Aggregation Strategy
RFC 1338

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Network Working Group                                         V. Fuller
Request for Comments: 1338                                      BARRNet
                                                                  T. Li
                                                                  cisco
                                                                  J. Yu
                                                                  MERIT
                                                            K. Varadhan
                                                                 OARnet
                                                              June 1992

      Supernetting: an Address Assignment and Aggregation Strategy

Status of this Memo

   This memo provides information for the Internet community. It does
   not specify an Internet standard.  Distribution of this memo is
   unlimited.

Abstract

   This memo discusses strategies for address assignment of the existing
   IP address space with a view to conserve the address space and stem
   the explosive growth of routing tables in default-route-free routers
   run by transit routing domain providers.

Table of Contents

   Acknowledgements .................................................  2
   1.  Problem, goal, and motivation ................................  2
   2.  Scheme plan ..................................................  3
   2.1.  Aggregation and its limitations ............................  3
   2.2.  Distributed network number allocation ......................  5
   3.  Cost-benefit analysis ........................................  6
   3.1.  Present allocation figures .................................  7
   3.2.  Historic growth rates ......................................  8
   3.3.  Detailed analysis ..........................................  8
   3.3.1.  Benefits of new addressing plan ..........................  9
   3.3.2.  Growth rate projections ..................................  9
   4.  Changes to Inter-Domain routing protocols .................... 11
   4.1.  General semantic changes ................................... 11
   4.2.  Rules for route advertisement .............................. 11
   4.3.  How the rules work ......................................... 13
   4.4.  Responsibility for and configuration of aggregation ........ 14
   5.  Example of new allocation and routing ........................ 15
   5.1.  Address allocation ......................................... 15
   5.2.  Routing advertisements ..................................... 17
   6.  Transitioning to a long term solution ........................ 18

Fuller, Li, Yu, & Varadhan                                      [Page 1]
RFC 1338                      Supernetting                     June 1992

   7.  Conclusions .................................................. 18
   8.  Recommendations .............................................. 18
   9.  Bibliography ................................................. 19
   10. Security Considerations ...................................... 19
   11. Authors' Addresses ........................................... 19

Acknowledgements

   The authors wish to express their appreciation to the members of the
   ROAD group with whom many of the ideas contained in this document
   were inspired and developed.

1.    Problem, Goal, and Motivation

   As the Internet has evolved and grown over in recent years, it has
   become painfully 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 to large to be widely allocated.

        2.   Growth of routing tables in Internet routers beyond the
             ability of current software (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.

   The proposed solution is to hierarchically allocate future IP address
   assignment, by delegating control of segments of the IP address space
   to the various network service providers.

   It is proposed that this scheme of allocating IP addresses be