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



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  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).





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  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: [email protected]


  Scott Bradner
  Harvard University
  1350 Mass Ave, Rm 813
  Cambridge MA 02138

  Phone: +1 617 495 3864
  EMail: [email protected]

















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