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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 22 Configuring IP Unicast Routing
Configuring IGRP
If variance is configured as described in the preceding section, IGRP or Enhanced IGRP distributes
traffic among multiple routes of unequal cost to the same destination. If you want faster convergence to
alternate routes, but you do not want to send traffic across inferior routes in the normal case, you might
prefer to have no traffic flow along routes with higher metrics. Use the traffic-share router
configuration command to control distribution of traffic among multiple routes of unequal cost.
Note
For more information and examples, refer to the Cisco IOS IP and IP Routing Configuration Guide
for Release 12.1.
Beginning in privileged EXEC mode, follow these steps to configure IGRP. Configuring the routing
process is required; other steps are optional:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
router igrp autonomous-system
Enable an IGRP routing process, and enter router configuration mode. The
autonomous system number identifies the routes to other IGRP routers and
tags routing information.
Step 3
network network-number
Associate networks with an IGRP routing process. IGRP sends updates to
the interfaces in the specified networks. If an interface’s network is not
specified, it is not advertised in any IGRP update. It is not necessary to have
a registered autonomous system number, but if you do have a registered
number, we recommend that you use it to identify your process.
Step 4
offset list [access-list number | name]
{in | out} offset [type number]
(Optional) Apply an offset list to routing metrics to increase incoming and
outgoing metrics to routes learned through IGRP. You can limit the offset
list with an access list or an interface.
Step 5
neighbor ip-address
(Optional) Define a neighboring router with which to exchange routing
information. This step allows routing updates from RIP (normally a
broadcast protocol) to reach nonbroadcast network.
Step 6
metric weights tos k1 k2 k3 k4 k5
(Optional) Adjust the IGRP metric. By default, the IGRP composite metric
is a 23-bit quantity that is the sum of the segment delays and the lowest
segment bandwidth for a given route.
•
tos—Type of services; the default is 0.
•
k1-k5—Constants that convert a metric vector into a scalar quantity.
Defaults for k1 and k3 are 1; all others are 0.
Step 7
timers basic update invalid holddown
flush [sleeptime]
(Optional) Adjust routing protocol timers.
•
update—The time (in seconds) between sending of routing updates.
The default is 90 seconds.
•
invalid—The timer interval (in seconds) after which a route is declared
invalid. The default is 270 seconds.
•
holddown—The time (in seconds) during which routing information
about better paths is suppressed. The default is 280 seconds.
•
flush—The time (in seconds) that must pass before a route is removed
from the routing table. The default is 630 seconds.
•
sleeptime—Interval in milliseconds for postponing routing updates.
The default is 0.
