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 other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, 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 . 2 Components of the Architecture The CIDR architecture is described in the following documents: - "An Architecture for IP Address Allocation with CIDR"  - "Classless Inter-Domain Routing (CIDR): An Address Assignment and Aggregation Strategy"  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"  provides specific recommendations for assigning IP addresses that are consistent with  and , and "Schedule for Address Space Management Guidelines"  describes the timetable for deploying  in the Internet. Both  and  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  Inter-Domain Routing Protocol for IP  Inter-Domain routing protocols which do not meet these requirements are: Border Gateway Protocol version 3  Exterior Gateway Protocol  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  Dual-ISIS  RIP Version 2  The Intra-Domain routing protocol which is not CIDR capable is: RIP Version 1  3 Applicability of CIDR The CIDR architecture is applicable to any group of connected domains that supports IP version 4   . 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: email@example.com 5. REFERENCES  Gross, P., Almquist, P., "IESG Deliberations on Routing and Addressing", RFC1380, November 1992  Rekhter, Y., Li, T., "An Architecture for IP Address Allocation with CIDR" (currently an internet-draft)  Fuller, V., Li, T., Yu, J., and Varadhan, K., "Classless Inter- Domain Routing (CIDR): An Address Assignment and Aggregation Strategy" (revision of RFC 1338)  Gerich, E., "Guidelines for Management of IP Address Space", RFC1366, October 1992  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)  Rekhter, Y., Li, T., "A Border Gateway Protocol 4 (BGP-4)", IETF Working Paper.  Hares, S., "IDRP for IP", Internet Draft, <draft-hares-idrp-04.txt>  Lougheed, K., Rekhter, Y., "A Border Gateway Protocol 3 (BGP-3)", RFC 1267, October 1991.  Rosen, E.C., "Exterior Gateway Protocol EGP", RFC 827, October 1992.  Moy, J., "OSPF Version 2", RFC 1247, Proteon, Inc., July 1991.  Callon, R. "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", RFC1195, December 1990.  Malkin, G. "RIP Version 2 Carrying Additional Information", RFC 1388, January 1993.  Hedrick, C. "Routing Information Protocol", RFC 1058, June 1988.  Postel, J.B. "Internet Protocol", RFC 791, September 1981.  Braden, R., Editor, "Requirements for Internet Hosts -- Communication Layers", IETF, STD 3, RFC 1122, October 1989.  Almquist, P., Editor, "Requirements for IP Routers", Work in Preparation, IETF.