Movatterモバイル変換

Network Working Group                                       B. CarpenterRequest for Comments: 1900                                    Y. RekhterCategory: Informational                                              IAB                                                           February 1996Renumbering Needs WorkStatus 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 Contents1. Motivation...................................................12. DNS versus IP Addresses......................................23. Recommendations..............................................34. Security Considerations......................................4   Acknowledgements................................................4   Authors' Addresses..............................................41. 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.Carpenter & Rekhter          Informational                      [Page 1]

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   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, seeRFC 1594) for servers and many user systems, areCarpenter & Rekhter          Informational                      [Page 2]

RFC 1900                 Renumbering Needs Work            February 1996   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.Carpenter & Rekhter          Informational                      [Page 3]

RFC 1900                 Renumbering Needs Work            February 1996   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: brian@dxcoms.cern.ch   Yakov Rekhter   cisco Systems   170 West Tasman Drive   San Jose, CA 95134   Phone: (914) 528-0090   EMail: yakov@cisco.comCarpenter & Rekhter          Informational                      [Page 4]