Cisco Systems: An Introduction to IGRP (IP Routing)

An Introduction to IGRP  [IP Routing] - Cisco Systems

Introduction
In general, load balancing is the capability of a router to distribute
traffic over all the router network ports that are the same distance from the
destination address. Load balancing increases the utilization of network
segments, and so increases effective network bandwidth. There are two types of
load balancing:

• Equal cost path
• Unequal cost path

This document explains how unequal cost path load balancing works in
Enhanced Interior Gateway Routing Protocol (EIGRP).


Goals for IGRP
The IGRP protocol allows a number of gateways to coordinate their routing. Its goals are the following:

• Stable routing even in very large or complex networks. No routing loops should occur, even as transients.
  Fast response to changes in network topology.
 
• Low overhead. That is, IGRP itself should not use more bandwidth than what is actually needed for its task.
  
• Splitting traffic among several parallel routes when they are of roughly equal desirability.
  
• Taking into account error rates and level of traffic on different paths.

The current implementation of IGRP handles routing for TCP/IP. However, the basic design is intended to be able to handle a variety of protocols.