Nokia Network Voyager for IPSO 4.0 Reference Guide 385 Graft—Traces graft and graft acknowledgment packetsIGRPThe Inter-Gateway Routing Protocol (IGRP) is a widely used interior gateway protocol (IGP).Like RIP, IGRP is an implementation of a distance-vector, or Bellman-Ford, routing protocol forlocal networks. As specified, IGRP modifies the basic Bellman-Ford algorithm in three ways: Uses a vector of metrics. Allows for multiple paths to a single destination, thus allowing for load sharing. Provides stability during topology changes because new features.This document provides background information and cites differences with other IGRPimplementations.A router running IGRP broadcasts routing updates at periodic intervals, in addition to updatesthat are sent immediately in response to some type of topology change. An update messageincludes the following information: Configured autonomous system number Current edition number of the routing table Checksum of the update message Count of the number of routes included List of route entriesAn IGRP update packet contains three types of routine entries. Interior System ExteriorEach entry includes three bytes of an IP address. The fourth byte is determined by the type of theroute entry. Interior routes are passed between links that are subnetted from the same class IPaddress. System routes are classful IP routes exchanged within an autonomous system. Exteriorroutes are like system routes, but also are used for installing a default route. In addition, thefollowing metrics are included for each entry: Delay Bandwidth Math MTU Reliability Load Hop countIGRP calculates a single composite metric from this vector to compare routes. Since the metricsattempt to physically characterize the path to a destination, IGRP attempts to provide optimalrouting.IGRP has two packet types.
