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Versions: 00 RFC 1517

INTERNET-DRAFT                      Internet Engineering Steering Group
March 1993

            Applicability Statement for the Implementation of
                  Classless Inter-Domain Routing (CIDR)

Abstract
--------

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.  Internet Drafts may be updated, replaced, or obsoleted by
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   Please check the 1id-abstracts.txt listing contained in the
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   nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
   current status of any Internet Draft.

   This memo is an draft IESG standards track Applicability Statement for
   the Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Official
   Internet Protocol Standards" for the standardization state and status
   of this specification.  Distribution of this memo is unlimited.


1   Introduction

   As the Internet has evolved and grown in recent years, it has become
   clear that it will soon face several serious scaling problems. These
   include:

       - Exhaustion of the class-B network address space. One
         fundamental cause of this problem is the lack of a network
         class of a size that is appropriate for a mid-sized
         organization. Class-C, with a maximum of 254 host addresses, is
         too small, while class-B, which allows up to 65534 addresses,
         is too large to be densely populated.  The result is inefficient
         utilization of class-B network numbers.

       - Routing information overload. The size and rate of growth of the
         routing tables in Internet routers is beyond the ability of current
         software (and people) to effectively manage.

       - Eventual exhaustion of IP network numbers.

   It has become clear that the first two of these problems are likely
   to become critical in the near term.  Classless
   Inter-Domain Routing (CIDR) attempts to deal with these problems by
   defining a mechanism to slow the growth of routing tables and reduce
   the need to allocate new IP network numbers.  It does not attempt to
   solve the third problem, which is of a more long-term nature, but
   instead endeavors to ease enough of the short to mid-term
   difficulties to allow the Internet to continue to function
   efficiently while progress is made on a longer-term solution.

   The IESG, after a thorough discussion in the IETF, in June 1992
   selected CIDR as the solution for the short term routing table
   explosion problem [1].


2 Components of the Architecture

   The CIDR architecture is described in the following documents:

       - "An Architecture for IP Address Allocation with CIDR" [2]

       - "Classless Inter-Domain Routing (CIDR):  An Address Assignment
         and Aggregation Strategy" [3]

   The first of these documents presents the overall architecture of CIDR;
   the second describes the specific address allocation scheme to be used.

   In addition to these two documents, "Guidelines for Management of IP
   Address Space" [4] provides specific recommendations for assigning IP
   addresses that are consistent with [2] and [3], and "Schedule for Address
   Space Management Guidelines" [5] describes the timetable for deploying
   [4] in the Internet.  Both [4] and [5] should be viewed as supporting,
   rather than defining, documents.

   In addition to the documents mentioned above, CIDR requires that
   inter-domain routing protocols be capable of handling reachability
   information that is expressed solely in terms of IP address prefixes.
   While several inter-domain routing protocols are capable of
   supporting such functionality, this Applicability Statement does not
   mandate the use of a particular one.  The inter-domain protocols which
   meets this requirement is:

       Border Gateway Protocol version 4 [6]
       Inter-Domain Routing Protocol for IP [7]

   Inter-Domain routing protocols which do not meet these requirements
   are:

       Border Gateway Protocol version 3 [8]
       Exterior Gateway Protocol [9]

   While CIDR does not require intra-domain routing protocols to also be
   CIDR capable, it highly recommends that intra-domain routing protocols

   Although CIDR does not require that intra-domain routing protocols, as
   well as inter-domain routing protocols, be capable of supporting CIDR,
   the benefits of implementing CIDR will be greater if this is the case.
   If this is not done, then the CIDR route aggregation will need to be
   undone inside of a routing domain.  The CIDR capable intra-domain
   routing protocols are:

       Open Shortest Path Routing Protocol [10]
       Dual-ISIS [11]
       RIP Version 2 [12]

   The Intra-Domain routing protocol which is not CIDR capable is:

       RIP Version 1 [13]


3 Applicability of CIDR

   The CIDR architecture is applicable to any group of connected domains
   that supports IP version 4 [14] [15] [16].  CIDR does not require all
   of the domains in the Internet to be converted to use CIDR. On the
   contrary, it assumes that some of the existing domains in the Internet
   will never be able to convert.  Despite this, CIDR will still provide
   connectivity to such places, although the optimality of routes to
   these places may be impacted.

   This Applicability Statement requires Internet domains providing
   backbone and/or transit service to fully implement CIDR in order to
   ensure that the growth of the resources required by routers to provide
   Internet-wide connectivity will be significantly slower than the
   growth of the number of assigned networks.

   This Applicability Statement strongly recommends that all
   non-backbone/transit Internet domains also implement CIDR because it
   will reduce the amount of routing information inside of these domains.

   Individual domains are free to choose whatever inter-domain and
   intra-domain routing architectures best meet their requirements.
   Specifically, this Applicability Statement does not prevent a domain
   or a group of domains from using addressing schemes which do not
   conform to CIDR.  Subject to the available resources in routers, CIDR
   should be able to co-exist with other addressing schemes without
   adversely impacting overall connectivity.


3. SECURITY CONSIDERATIONS

Security issues are not discussed in this memo.


4. CONTACT INFORMATION

Robert M. Hinden
Sun Microsystems
2550 Garcia Ave, MS MTV5-44
Mt. View, CA 94043

Phone: (415) 336-2082
Fax:   (415) 336-6015

Email: hinden@eng.sun.com

5. REFERENCES

    [1]  Gross, P., Almquist, P., "IESG Deliberations on Routing and
         Addressing", RFC1380, November 1992

    [2]  Rekhter, Y., Li, T., "An Architecture for IP Address Allocation
         with CIDR" (currently an internet-draft)

    [3]  Fuller, V., Li, T., Yu, J., and Varadhan, K., "Classless Inter-
         Domain Routing (CIDR): An Address Assignment and Aggregation
         Strategy" (revision of RFC 1338)

    [4]  Gerich, E., "Guidelines for Management of IP Address Space",
         RFC1366, October 1992

    [5]  Topolcic, C., "Schedule for address space management guidelines",
         RFC 1367, October 1992 (the IESG has expressed an interest in
         seeing this schedule revised to reflect the entire Internet; it is
         currently US-centric)

    [6]  Rekhter, Y., Li, T., "A Border Gateway Protocol 4 (BGP-4)",
         IETF Working Paper.

    [7]  Hares, S., "IDRP for IP", Internet Draft,
         <draft-hares-idrp-04.txt>

    [8]  Lougheed, K., Rekhter, Y., "A Border Gateway Protocol 3
         (BGP-3)", RFC 1267, October 1991.

    [9]  Rosen, E.C., "Exterior Gateway Protocol EGP", RFC 827, October
         1992.

    [10] Moy, J., "OSPF Version 2", RFC 1247, Proteon, Inc., July
         1991.

    [11] Callon, R. "Use of OSI IS-IS for Routing in TCP/IP and Dual
         Environments", RFC1195, December 1990.

    [12] Malkin, G. "RIP Version 2 Carrying Additional Information",
         RFC 1388, January 1993.

    [13] Hedrick, C. "Routing Information Protocol", RFC 1058, June
         1988.

    [14] Postel,  J.B. "Internet Protocol", RFC 791, September 1981.

    [15] Braden, R., Editor, "Requirements for Internet Hosts -- Communication
         Layers", IETF, STD 3, RFC 1122, October 1989.

    [16] Almquist, P., Editor, "Requirements for IP Routers", Work in
         Preparation, IETF.


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