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Cisco IOS in a Nutshell, 2nd Edition by James Boney

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Name

variance — EIGRP, IGRP

Synopsis

variance multipler-value
no variance multipler-value

Configures

Multiplier value for load balancing

Default

1 (equal-cost load balancing)

Description

This command lets you specify a multiplier-value for use in load balancing with IGRP and EIGRP. The multiplier-value can be from 1 to 128. Routes within a factor of multiplier-value of the best routes are used to carry traffic. Normally, all traffic is sent over the route with the best metric; if two or more routes share the same metric, load balancing takes place between those routes.

Example

Assume that your router has three routes to the same destination. The routes have metrics of 10, 30, and 50. With the default variance of 1 (equal-cost load balancing), all traffic is sent using the route with the metric of 10. For load balancing to take place, another route with a metric of 10 must appear in the routing table.

To force the router to use multiple paths in this situation, you can change the variance (unequal-cost load balancing). If you increase the variance to 3, routes with a metric within a factor of 3 of the best route are used. In this situation, the routes with metrics of 10 and 30 will be used to carry traffic, and the route with a metric of 50 will not.

router eigrp 100
    variance 5

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