Cisco Systems 78-11741-02 Adjusting the Igrp Metric Weights, Adjusts the Igrp metric, IPC-217

Configuring IGRP

IGRP Configuration Task List

To control how traffic is distributed among multiple routes of unequal cost, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# traffic-share balanced	Distribute traffic proportionately to the ratios of metrics.

Adjusting the IGRP Metric Weights

You have the option of altering the default behavior of IGRP routing and metric computations. For example, you can tune system behavior to allow for transmissions via satellite. Although IGRP metric defaults were carefully selected to provide excellent operation in most networks, you can adjust the IGRP metric. Adjusting IGRP metric weights can dramatically affect network performance, however, so ensure that you make all metric adjustments carefully.

To adjust the IGRP metric weights, use the following command in router configuration mode. Because of the complexity of this command, we recommend that you only use it with guidance from an experienced system designer.

Command	Purpose
Router(config-router)# metric weights tos k1 k2 k3 k4 k5	Adjusts the IGRP metric.

By default, the IGRP composite metric is a 24-bit quantity that is a sum of the segment delays and the lowest segment bandwidth (scaled and inverted) for a given route. For a network of homogeneous media, this metric reduces to a hop count. For a network of mixed media (Ethernet, FDDI, and serial lines running from 9600 bits per second to T1 rates), the route with the lowest metric reflects the most desirable path to a destination.

Adjusting Timers

Routing protocols use several timers that determine such variables as the frequency of routing updates, the length of time before a route becomes invalid, and other parameters. You can adjust these timers to tune routing protocol performance to better suit your internetwork needs. You can make the following timer adjustments:

•The rate (time in seconds between updates) at which routing updates are sent

•The interval of time (in seconds) after which a route is declared invalid

•The interval (in seconds) during which routing information regarding better paths is suppressed

•The amount of time (in seconds) that must pass before a route is removed from the routing table

•The amount of time for which routing updates will be postponed

It also is possible to tune the IP routing support in the software to enable faster convergence of the various IP routing algorithms, and, hence, quicker fallback to redundant routers. The total effect is to minimize disruptions to end users of the network in situations where quick recovery is essential.

Cisco IOS IP Configuration Guide

IPC-217