RFC 1519 (rfc1519) - Page 1 of 24

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

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Network Working Group                                          V. Fuller
Request for Comments: 1519                                       BARRNet
Obsoletes: 1338                                                    T. Li
Category: Standards Track                                          cisco
                                                                   J. Yu
                                                                   MERIT
                                                             K. Varadhan
                                                                  OARnet
                                                          September 1993


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

Status of this Memo

   This RFC specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" for the standardization state and status
   of this protocol.  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.

Table of Contents

   Acknowledgements .................................................  2
   1.  Problem, Goal, and Motivation ................................  2
   2.  CIDR address allocation ......................................  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 and practices ...... 11
   4.1  Protocol-independent 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
   4.5  Intra-domain protocol considerations ........................ 15
   5.  Example of new allocation and routing ........................ 15



Fuller, Li, Yu & Varadhan
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