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.





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  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
  independent of the IP address space.  DNS names are usually related
  to the ownership and function of the hosts, not to the mechanisms of
  addressing and routing.  A change in DNS name may be a sign of a real
  change in function or ownership, whereas a change in IP address is a
  purely technical event.

  Expressing information in terms of Domain Names allows one to defer
  binding between a particular network entity and its IP address until
  run time. Domain Names for enterprises, and Fully Qualified Domain
  Names (FQDNs, see RFC 1594) for servers and many user systems, are



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  expected to be fairly long-lived, and more stable than IP addresses.
  Deferring the binding avoids the risk of changed mapping between IP
  addresses and specific network entities (due to changing addressing
  information).  Moreover, reliance on FQDNs (rather than IP addresses)
  also localizes to the DNS the changes needed to deal with changing
  addressing information due to renumbering.

  In some cases, both the addresses and FQDNs of desk top or portable
  systems are allocated dynamically. It is only a highly responsive
  dynamic DNS update mechanism that can cope with this.

3. Recommendations

  To make renumbering more feasible, the IAB strongly recommends that
  all designs and implementations should minimise the cases in which IP
  addresses are stored in non-volatile storage maintained by humans,
  such as configuration files.  Configuration information used by
  TCP/IP protocols should be expressed, whenever possible, in terms of
  Fully Qualified Domain Names, rather than IP addresses. Hardcoding IP
  addresses into applications should be deprecated.  Files containing
  lists of name to address mappings, other than that used as part of
  DNS configuration, should be deprecated, and avoided wherever
  possible.

  There are times when legacy applications which require configuration
  files with IP addresses rather than Domain Names cannot be upgraded
  to meet these recommendations. In those cases, it is recommended that
  the configuration files be generated automatically from another file
  which uses Domain Names, with the substitution of addresses being
  done by lookup in the DNS.

  Use of licensing technology that is based upon the IP address of a
  host system makes renumbering quite difficult. Therefore, the use of
  such technology should be strongly discouraged.

  The development and deployment of a toolkit to facilitate and
  automate host renumbering is essential.  The Dynamic Host
  Configuration Protocol (DHCP) is clearly an essential part of such a
  toolkit.  The IAB strongly encourages implementation and wide-scale
  deployment of DHCP.  Dynamic router discovery (RFC 1256) and service
  location (work in progress in the IETF) also belong in this toolkit.
  Support for dynamic update capabilities to the Domain Name System
  (DNS) that could be done with sufficient authentication would further
  facilitate host renumbering.  The IAB strongly encourages progression
  of work in this area towards standardization within the IETF, with
  the goal of integrating DHCP and dynamic update capabilities to
  provide truly autoconfigurable TCP/IP hosts.




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  The IAB strongly encourages sharing of experience with renumbering
  and documenting this sharing within the Internet community.  The IAB
  suggests that the IETF (and specifically its Operational Requirements
  Area) may be the most appropriate place to develop such
  documentation.  The IAB welcomes the creation of the PIER (Procedures
  for Internet and Enterprise Renumbering) working group.

4. Security Considerations

  Renumbering is believed to be compatible with the Internet security
  architecture, as long as addresses do not change during the lifetime
  of a security association.

Acknowledgements

  This document is a collective product of the Internet Architecture
  Board.

  Useful comments were received from several people, especially Michael
  Patton, Steve Bellovin, Jeff Schiller, and Bill Simpson.

Authors' Addresses

  Brian E. Carpenter
  Group Leader, Communications Systems
  Computing and Networks Division
  CERN
  European Laboratory for Particle Physics
  1211 Geneva 23, Switzerland

  Phone:  +41 22 767-4967
  Fax:    +41 22 767-7155
  Telex:  419000 cer ch
  EMail: [email protected]


  Yakov Rekhter
  cisco Systems
  170 West Tasman Drive
  San Jose, CA 95134

  Phone: (914) 528-0090
  EMail: [email protected]








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