IAB B. Carpenter
Internet Draft Y. Rekhter
October 1995
Renumbering Needs Work
Abstract
draft-iab-renum-02.txt
Renumbering, i.e. changes in the IP addressing information of various
network components, is likely to become more and more widespread and
common, and in many cases unavoidable. The IAB would like to stress
the need to develop and deploy solutions that would facilitate such
changes.
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
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To learn the current status of any Internet-Draft, please check the
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Table of Contents:
Status of this Memo.............................................1
1. Motivation...................................................2
2. DNS versus IP Addresses......................................2
3. Recommendations..............................................3
4. Security considerations......................................4
Acknowledgements................................................5
Authors' Addresses..............................................5
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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".
Voluntary 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 voluntary renumbering could
occur.
Increasingly, renumbering will be unavoidable and involuntary.
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 the vast majority of Internet hosts and subnets to have
addresses belonging to a single large block of address space that has
been allocated to their current service provider. To contain the
growth of routing information, whenever a subscriber changes to a new
service provider, the subscriber'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 subscribers concerned
must renumber their subnet(s) and host(s). If the subscriber does
not renumber, the consequences depend on the exact policy of the
service provider. They may include either (a) limited (less than
Internet-wide) IP connectivity, or (b) extra cost to offset the
overhead associated with the subscriber's routing information that
Internet Services 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
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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 the 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 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.
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. 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.
The IAB strongly encourages sharing of experience with renumbering
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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 recent proposal to create a 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.
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Acknowledgements
This document is a collective product of the Internet Architecture
Board.
Useful comments were received from several people, especially Michael
Patton and Steve Bellovin.
Authors' Addresses
Brian E. Carpenter
Group Leader, Communications Systems Phone: +41 22 767-4967
Computing and Networks Division Fax: +41 22 767-7155
CERN Telex: 419000 cer ch
European Laboratory for Particle Physics Email: brian@dxcoms.cern.ch
1211 Geneva 23, Switzerland
Yakov Rekhter
cisco Systems
170 West Tasman Drive
San Jose, CA 95134
Phone: (914) 528-0090
EMail: yakov@cisco.com
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