CIDR and Classful Routing (RFC1817)
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
This document represents the IAB's (Internet Architecture Board) evaluation of the current and near term implications of CIDR on organizations that use Classful routing technology. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.
Network Working Group Y. Rekhter Request for Comments: 1817 cisco Systems Category: Informational August 1995
CIDR and Classful Routing
Status of this Memo
This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Classless Inter-Domain Routing (CIDR) is used in the Internet as the primary mechanism to improve scalability of the Internet routing system. This document represents the IAB’s (Internet Architecture Board) evaluation of the current and near term implications of CIDR on organizations that use Classful routing technology.
Classless Inter-Domain Routing (CIDR) ([RFC1518], [RFC1519]) is deployed in the Internet as the primary mechanism to improve scaling property of the Internet routing system. Essential to CIDR is the generalization of the concept of variable length subnet masks (VLSM) and the elimination of classes of network numbers (A, B, and C). The interior (intra-domain) routing protocols that support CIDR are OSPF, RIP II, Integrated IS-IS, and E-IGRP. The exterior (inter-domain) routing protocol that supports CIDR is BGP-4. Protocols like RIP, BGP-3, EGP, and IGRP do not support CIDR.
Implications of CIDR
Deployment of CIDR has certain implications on the segments of the Internet that are still using routing technology that can not support CIDR. Existing sites that rely solely on a default route for their external connectivity may not require support of VLSM capable routing technology for their interior routing and CIDR for their exterior routing. All sites lacking support for VLSM and CIDR capable routing must rely on a default route, which consequently may result in...