Network Working Group                                       B. Carpenter
Request for Comments: 1900                                    Y. Rekhter
Category: Informational                                              IAB
                                                           February 1996


                         Renumbering Needs Work

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.

Abstract

   Renumbering, i.e., changes in the IP addressing information of
   various network components, is likely to become more and more
   widespread and common. The Internet Architecture Board (IAB) would
   like to stress the need to develop and deploy solutions that would
   facilitate such changes.

Table of Contents

   1. Motivation................................................... 1
   2. DNS versus IP Addresses...................................... 2
   3. Recommendations.............................................. 3
   4. Security Considerations...................................... 4
   Acknowledgements................................................ 4
   Authors' Addresses.............................................. 4

1. Motivation

   Hosts in an IP network are identified by IP addresses, and the IP
   address prefixes of subnets are advertised by routing protocols.  A
   change in such IP addressing information associated with a host or
   subnet is known as "renumbering".

   Renumbering may occur for a variety of reasons.  For example, moving
   an IP host from one subnet to another requires changing the host's IP
   address.  Physically splitting a subnet due to traffic overload may
   also require renumbering.  A third example where renumbering may
   happen is when an organization changes its addressing plan.  Such
   changes imply changing not only hosts' addresses, but subnet numbers
   as well.  These are just three examples that illustrate possible
   scenarios where renumbering could occur.






 
RFC 1900                 Renumbering Needs Work            February 1996


   Increasingly, renumbering will be needed for organizations that
   require Internet-wide IP connectivity, but do not themselves provide
   a sufficient degree of address information aggregation.  Unless and
   until viable alternatives are developed, extended deployment of
   Classless Inter-Domain Routing (CIDR) is vital to keep the Internet
   routing system alive and to maintain continuous uninterrupted growth
   of the Internet.  With current IP technology, this requires such
   organizations to use addresses belonging to a single large block of
   address space, allocated to their current service provider which acts
   as an aggregator for these addresses.  To contain the growth of
   routing information, whenever such an organization changes to a new
   service provider, the organization's addresses will have to change.
   Occasionally, service providers themselves may have to change to a
   new and larger block of address space. In either of these cases, to
   contain the growth of routing information, the organizations
   concerned would need to renumber their subnet(s) and host(s). If the
   organization does not renumber, then some of the potential
   consequences may include (a) limited (less than Internet-wide) IP
   connectivity, or (b) extra cost to offset the overhead associated
   with the organization's routing information that Internet Service
   Providers have to maintain, or both.

   Currently, renumbering is usually a costly, tedious and error-prone
   process.  It normally requires the services of experts in the area
   and considerable advance planning.  Tools to facilitate renumbering
   are few, not widely available, and not widely deployed. While a
   variety of ad hoc approaches to renumbering have been developed and
   used, the overall situation is far from satisfactory.  There is
   little or no documentation that describes renumbering procedures.
   While renumbering occurs in various parts of the Internet, there is
   little or no documented experience sharing.

2. DNS versus IP Addresses

   Within the Internet architecture an individual host can be identified
   by the IP address(es) assigned to the network interface(s) on that
   host.  The Domain Name System (DNS) provides a convenient way to
   associate legible names with IP addresses.  The DNS name space is