Movatterモバイル変換

Network Working Group                Internet Engineering Steering GroupRequest for Comments: 1517                             R. Hinden, EditorCategory: Standards Track                                 September 1993Applicability Statement for the Implementation ofClassless Inter-Domain Routing (CIDR)Status of this Memo   This RFC specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" for the standardization state and status   of this protocol.  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) ttempts 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 tableIESG                                                            [Page 1]

RFC 1517              CIDR Applicability Statement        September 1993   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 "Status of CIDR   Deployment in the Internet" [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.   Although Internet routing domains are not required to use routing   protocols capable of propagating CIDR routes, the topology such   routing domains can support will be somewhat limited.  In particular,   the non-CIDR-capable parts of the Internet will need to default   towards the CIDR-capable parts of the Internet for routes which have   been aggregated to non-network boundaries.3. Applicability of CIDR   The CIDR architecture is applicable to any group of connected domains   that supports IP version 4 [6] [7].  CIDR does not require all of the   domains in the Internet to be converted to use CIDR. 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 toIESG                                                            [Page 2]

RFC 1517              CIDR Applicability Statement        September 1993   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.4. References   [1] Gross, P., and P. Almquist, "IESG Deliberations on Routing and       Addressing",RFC 1380, IESG Chair, IESG Internet AD, November       1992.   [2] Rekhter, Y., and T. Li, "An Architecture for IP Address       Allocation with CIDR",RFC 1518, T.J. Watson Research Center, IBM       Corp., cisco Systems, September 1993.   [3] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter-       Domain Routing (CIDR): An Address Assignment and Aggregation       Strategy",RFC 1519, BARRNet, cisco, Merit, and OARnet, September       1993.   [4] Gerich, E., "Guidelines for Management of IP Address Space",RFC1466, Merit, May 1993.   [5] Topolcic, C., "Status of CIDR Deployment in the Internet",RFC1467, CNRI, August 1993.   [6] Postel, J., "Internet Protocol - DARPA Internet Program Protocol       Specification", STD 5,RFC 791, USC/Information Sciences       Institute, September 1981.   [7] Braden, R., Editor, "Requirements for Internet Hosts --       Communication Layers", STD 3,RFC 1122, IETF, October 1989.5. Security Considerations   Security issues are not discussed in this memo.IESG                                                            [Page 3]

RFC 1517              CIDR Applicability Statement        September 19936. Author's Address   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.comIESG                                                            [Page 4]