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Chapter 6
IGRP and EIGRP
When redistributing static routes or other protocol types within IGRP,
metrics may be set for these routes as well by using the default-metric
command:
default-metric bandwidth delay reliability load MTU
The words in italics in the command above are just placeholders for variables
and should be replaced with numbers.
Bandwidth and delay have a range of values from 0 to 4,294,967,295 (in
Kbps) and 0 to 4,294,967,295 (in 10-microsecond units), respectively. Reli-
ability ranges from 0 to 255, with 255 being the most reliable. Load ranges
from 0 to 255; however, a value of 255 means that the link is completely
loaded. Finally, the value of MTU has the same range as the bandwidth vari-
able: 0 to 4,294,967,295.
When a router receives multiple routes for a specific network, one of the
routes must be chosen as the best route from all of the advertisements. The
router still knows that it is possible to get to a given network over multiple
interfaces, yet all data default to the best route.
IGRP provides the ability of unequal-cost load balancing. The variance
command is used to assign a weight to each feasible successor. A feasible suc-
cessor is a predetermined route to use should the most optimal path be lost.
The feasible successor can also be used as long as the secondary route con-
forms to the following three criteria, and an unequal-cost load balancing ses-
sion may be established:
A limit of four feasible successors may be used for load balancing.
Four is the default; the maximum number of feasible successors is six
for IOS version 11.0 and later.
The feasible successor's metric must fall within the specified variance
of the local metric.
The local metric must be greater than the metric for the next-hop
router.
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