RFC 1520 (rfc1520) - Page 3 of 9

Exchanging Routing Information Across Provider Boundaries in the CIDR Environment

RFC 1520           CIDR Provider Information Exchange     September 1993


3.  Assumptions on Deployment of CIDR in the Internet

   The document assumes that the CIDR deployment in the Internet will
   proceed as a three phase process.

   In the first phase all the major service providers will become CIDR-
   capable. Specifically, all the providers that can't rely on using
   Default route(s) for inter-domain routing (Type 1 providers) are
   expected to deploy BGP-4 and transition to CIDR during this phase. It
   is expected that CIDR reachability information will first appear in
   the Internet upon transition of all Type 1 service providers to CIDR.

   The second phase will commence upon completion of the first phase.
   During the second phase other service providers that are connected to
   the service providers that were transitioned to CIDR during the first
   phase will become CIDR-capable.  Specifically, during the second
   phase it is expected that most of the providers that need to acquire
   a large percentage of the total Internet routing information (Type 2
   provider) will become CIDR-capable.  In addition, during the second
   phase some of the Type 3 providers may become CIDR-capable as well.
   This plan was agreed to by a number of major providers [8]. NSFNET's
   steps to implement this plan are described in [9].

   Finally, during the third phase the rest of the Type 3 providers and
   most of the Type 4 providers will transition to CIDR.

   It is expected that the duration of the first phase will be
   significantly shorter than duration of the second phase.  Likewise,
   the duration of the second phase is expected to be shorter than the
   duration of the third phase.

   This document addresses the need for service providers to exchange
   inter-domain routing information during the second and third phases
   of this deployment. During these phases, some providers will be
   CIDR-capable, and others will not. Hence this document considers
   routing exchanges where one of the peers is CIDR-capable and the
   other is CIDR-incapable.

4.  Implications of CIDR on Interior Routing

   A CIDR-capable service provider can use the following two techniques
   to distribute exterior routing information to all of its routers
   (both interior and border):

      - utilize internal BGP/IDRP between all the routers

      - use CIDR-capable IGPs (e.g., OSPF, IS-IS, RIP2)




Rekhter & Topolcic