Load Balancing with EIGRP

RIP, RIPv2, IGRP, EIGRP and OSPF are all routing protocols that support equal cost load balancing but IGRP and EIGRP can also support unequal cost load balancing. However, unlike IGRP, EIGRP supports VLSM (Variable Length Subnet Masking). Below I use a Cisco 3560G router [IOS Version 12.2(40)SE] to show how you can have EIRGP load-balance across up to 32 links (equal or unequal). By default, EIGRP will provide equal-cost load balancing across up to 4 links. You can disable load balancing by setting the ‘maximum-paths’ to ‘1’.

To load-balance across unequal-cost links you will have to use the ‘variance’ command. By default, the variance metric is set to ‘1’ which means that only equal-cost links will load balance. The maximum value the variance metric can be set to is 128. So, for example, if you set the variance to ‘3’, any learned route with a metric less than or equal to three times the metric of the successor will be installed in the local routing table.