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Configuring IGRP
IGRP Configuration Task List
IPC-217
Cisco IOS IP Configuration Guide
To control how traffic is distributed among multiple routes of unequal cost, use the following command
in router configuration mode:
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.
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.
Command Purpose
Router(config-router)# traffic-share balanced
Distribute traffic proportionately to the ratios of metrics.
Command Purpose
Router(config-router)# metric weights tos k1 k2 k3 k4 k5
Adjusts the IGRP metric.