Routing Information Protocol
RFC 1058

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Network Working Group                                         C. Hedrick
Request for Comments: 1058                            Rutgers University
                                                               June 1988

                      Routing Information Protocol

Status of this Memo

   This RFC describes an existing protocol for exchanging routing
   information among gateways and other hosts.  It is intended to be
   used as a basis for developing gateway software for use in the
   Internet community.  Distribution of this memo is unlimited.

                             Table of Contents

   1. Introduction                                                     2
        1.1. Limitations of the protocol                               4
        1.2. Organization of this document                             4
   2. Distance Vector Algorithms                                       5
        2.1. Dealing with changes in topology                         11
        2.2. Preventing instability                                   12
             2.2.1. Split horizon                                     14
             2.2.2. Triggered updates                                 15
   3. Specifications for the protocol                                 16
        3.1. Message formats                                          18
        3.2. Addressing considerations                                20
        3.3. Timers                                                   23
        3.4. Input processing                                         24
             3.4.1. Request                                           25
             3.4.2. Response                                          26
        3.5. Output Processing                                        28
        3.6. Compatibility                                            31
   4. Control functions                                               31

Overview

   This memo is intended to do the following things:

      - Document a protocol and algorithms that are currently in
        wide use for routing, but which have never been formally
        documented.

      - Specify some improvements in the algorithms which will
        improve stability of the routes in large networks.  These
        improvements do not introduce any incompatibility with
        existing implementations.  They are to be incorporated into

Hedrick                                                         [Page 1]
RFC 1058              Routing Information Protocol             June 1988

        all implementations of this protocol.

      - Suggest some optional features to allow greater
        configurability and control.  These features were developed
        specifically to solve problems that have shown up in actual
        use by the NSFnet community.  However, they should have more
        general utility.

   The Routing Information Protocol (RIP) described here is loosely
   based on the program "routed", distributed with the 4.3 Berkeley
   Software Distribution.  However, there are several other
   implementations of what is supposed to be the same protocol.
   Unfortunately, these various implementations disagree in various
   details.  The specifications here represent a combination of features
   taken from various implementations.  We believe that a program
   designed according to this document will interoperate with routed,
   and with all other implementations of RIP of which we are aware.

   Note that this description adopts a different view than most existing
   implementations about when metrics should be incremented.  By making
   a corresponding change in the metric used for a local network, we
   have retained compatibility with other existing implementations.  See
   section 3.6 for details on this issue.

1. Introduction

   This memo describes one protocol in a series of routing protocols
   based on the Bellman-Ford (or distance vector) algorithm.  This
   algorithm has been used for routing computations in computer networks
   since the early days of the ARPANET.  The particular packet formats
   and protocol described here are based on the program "routed", which
   is included with the Berkeley distribution of Unix.  It has become a
   de facto standard for exchange of routing information among gateways
   and hosts.  It is implemented for this purpose by most commercial
   vendors of IP gateways.  Note, however, that many of these vendors
   have their own protocols which are used among their own gateways.

   This protocol is most useful as an "interior gateway protocol".  In a
   nationwide network such as the current Internet, it is very unlikely
   that a single routing protocol will used for the whole network.
   Rather, the network will be organized as a collection of "autonomous
   systems".  An autonomous system will in general be administered by a
   single entity, or at least will have some reasonable degree of
   technical and administrative control.  Each autonomous system will