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rfc:rfc1923

Network Working Group J. Halpern Request for Comments: 1923 Newbridge Networks Category: Informational S. Bradner

                                                    Harvard University
                                                            March 1996
         RIPv1 Applicability Statement for Historic Status

Status 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 by RFC 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 assumes

Halpern & 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.edu

Halpern & Bradner Informational [Page 3]

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