Movatterモバイル変換

Network Working Group                                         J. HalpernRequest for Comments: 1923                            Newbridge NetworksCategory: Informational                                       S. Bradner                                                      Harvard University                                                              March 1996RIPv1 Applicability Statement for Historic StatusStatus 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   RIP Version 1 [RFC-1058] has been declared an historic document.   This Applicability statement provides the supporting motivation for   that declaration.  The primary reason, as described below, is the   Classful nature of RIPv1.1.0 Introduction   RIP version 1 (RIPv1) (as defined byRFC 1058) was one of the first   dynamic routing protocols used in the internet.  It was developed as   a technique for passing around network reachability information for   what we now consider relatively simple topologies.   The Internet has changed significantly since RIPv1 was defined,   particularly with the introduction and use of subnets and CIDR.   While RIPv1 is widely used in private networks, it can no longer be   considered applicable for use in the global Internet.2.0 RIPv1 restrictions   RIPv1 has a number of restrictions and behaviors which restrict its   useability in the global Internet.2.1 Classfulness   Chief among these is that it is a classful routing protocol.  RIP   packets do not carry prefix masks.  The prefix length is inferred   from the address.  For non-local addresses, the prefix is always the   "natural" (classful) length. (e.g., 24 bits for a "Class C" network   address.)  For networks to which a local interface exists, if the   interface is subnetted with some specific mask, then RIPv1 assumesHalpern & Bradner            Informational                      [Page 1]

RFC 1923   RIPv1 Applicability Statement for Historic Status  March 1996   that the mask used locally is the correct mask to apply for all   subnets of that network.   This has a number of effects.   1) RIPv1 can not be used with variable length subnetting.  In the      presence of variable length subnetting it will consistently      misinterpret prefix lengths.   2) RIPv1 is difficult to use with supernetting.  All CIDR supernets      must be exploded and advertised to RIPv1 as individual "natural"      classful advertisements.   3) Even when the networks running RIPv1 are themselves only subnetted      in fixed ways, if the remainder of the network has variable      subnetting then one must carefully make sure that RIPv1 does not      destroy the mask information when it passes through those subnets      running RIPv1.  Put another way, co-existence with mutual      information exchange between RIPv1 and more advanced routing      protocols is problematic at best.  Note that this applies even when      the other routing protocol is RIPv2.   4) The Internet will soon be making use of addresses which appear to      RIPv1 to be parts of Class A networks. Networks using RIPv1 may not      be able to reach all sites assigned the subsections of a single A.2.2 Simple Distance Vector   RIPv1 is a simple distance vector protocol.  It has been enhanced   with various techniques, including Split Horizon and Poison Reverse   in order to enable it to perform better in somewhat complicated   networks.   However, being a simple distance vector protocol, it will run into   difficulty. First and foremost, it will occasionally have to count to   infinity in order to purge bad routes.  This delays the convergence   of routing.  In order to keep this short, RIPv1 defines infinity as   16 hops.  That means that networks with diameters larger than that   can not use RIP.  Even getting close to that limit can cause   confusion for some implementations.3.0 Conclusion   The recommendation of this Applicability statement is that if there   is reason to run RIP in a network environment, one should use RIPv2   (RFC 1723).Halpern & Bradner            Informational                      [Page 2]

RFC 1923   RIPv1 Applicability Statement for Historic Status  March 1996   RIPv1 itself should only be used in simple topologies, with simple   reachability. It may be used by any site which uses fixed subnetting   internally, and either uses a default route to deal with external   traffic or is not connected to the global Internet or to other   organizations.   RIPv1 may also be used as a local advertising technology if the   information to be used fits within its capabilities.4.0 Security Considerations   RIPv1 includes no security functions.  RIPv2 includes a mechanism for   authenticating the sender of the routing information.  Sites which   are worried about the vulnerability of their routing infrastructure   and which feel they must run a RIP-like protocol should use RIPv2.5.0 Authors' Addresses   Joel M. Halpern   Newbridge Networks Inc.   593 Herndon Parkway Herndon,   VA 22070-5241   Phone: +1 703 708 5954   EMail: jhalpern@newbridge.com   Scott Bradner   Harvard University   1350 Mass Ave, Rm 813   Cambridge MA 02138   Phone: +1 617 495 3864   EMail: sob@harvard.eduHalpern & Bradner            Informational                      [Page 3]