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Interior Gateway Routing Protocol
After you enable IGRP on a router, metric weights can be changed using the
following command:
metric weights tos K1 K2 K3 K4 K5
Table 6.2 shows the relationship between the constant and the metric it
Each constant is used to assign a weight to a specific variable. This means
that when the metric is calculated, the algorithm will assign a greater impor-
tance to the specified metric. By assigning a weight, you are able to specify
what is most important. If bandwidth is of greatest concern to a network
administrator, then a greater weight would be assigned to K1. If delay is
unacceptable, then the K2 constant should be assigned a greater weight. The
tos variable is the type of service.
As well as tuning the actual metric weights, you can do other tunings. All
routing protocols have an administrative distance associated with the proto-
col type. If multiple protocols are running on one router, the administrative
distance value helps the router decide which path is best. The protocol with
the lowest administrative distance will be chosen. IGRP has a default admin-
istrative distance of 100. The tuning of this value is accomplished with the
command, like this:
distance 1­255
Valid values for the administrative distance range from 1 to 255. Again, the
lower the value, the better.
T A B L E 6 . 2
Metric Association of K Values
Bandwidth (B
Delay (D
Reliability (r)
Load (utilization on path)
Copyright ©2001 SYBEX , Inc., Alameda, CA