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Chapter 6

IGRP and EIGRP

Router(config-router)#network 10.0.0.0

Router(config-router)#^Z

Router#

Unfortunately, EIGRP assumes that all serial connections use T1 speeds.

In order to identify slower links, such as a 128K link, you must identify it
manually. Bandwidth is one of the two default metrics used to calculate a
route's metric. If the bandwidth is slower or faster than T1 speeds, use the
bandwidth

command followed by the bandwidth in kilobits in Interface

Configuration mode. The possible values are between 1 and 10,000,000.

If you need to stop routing updates from being sent on an interface, such

as a BRI interface, you can flag the interface as a passive interface. To do this
from an EIGRP session, use the passive-interface interface-type
interface-number

command. The interface-type portion defines the

type of interface, and the interface-number portion defines the number of
the interface.

EIGRP Tuning

The metrics used with EIGRP are tuned in the same manner as the metrics for
IGRP. Metrics are tuned to change the manner in which routes are calcu-
lated. The same command as for IGRP is also used:

metric weights tos K1 K2 K3 K4 K5

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, a greater weight should be assigned to K1. If delay is unac-
ceptable, the K2 constant should be assigned a greater weight. The tos vari-
able is the type of service. Refer back to Table 6.2 for the relationship
between the constant and the metric it affects. Also, remember that EIGRP
uses bandwidth and delay by default only when calculating routes.

Other tuning is possible. All routing protocols have an administrative dis-

tance associated with the protocol 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 lower administrative distance will be cho-
sen. EIGRP has a default administrative distance of 90 for internal routes
and 170 for external routes. Use the following command to make changes:

distance 1255

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