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Enhanced Interior Gateway Routing Protocol

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In this output, the feasible distance is the same for all three links. This

means that traffic will be load balanced (shared) across all three links
equally.

There will also be situations where there are multiple links to a given des-

tination, but the links have different next-hops. The metric for these links
will not likely be the same. Even though each link may have a different cost
assigned to it, EIGRP does allow for unequal-cost load balancing.

This is achieved by using the variance command--the same command

used in IGRP for unequal-cost load balancing:

variance multiplier

The variance command uses a multiplier, which can be a value from 1 to
128. The default setting for the multiplier is 1. This command must be used
inside the EIGRP protocol configuration.

Route Redistribution

When a router has more than one routed protocol configured, each EIGRP
session is defined by the autonomous system number used when enabling
EIGRP. With all of the different protocols and sessions running on a router,
it becomes important that the information learned by each session can be
shared with the other protocols and sessions. Route redistribution is the fea-
ture that allows for the exchange of route information among multiple pro-
tocols and multiple sessions.

The router where multiple protocols or sessions meet is called the Auton-

omous System Boundary Router (ASBR). When routes from one protocol or
session are injected or redistributed into another protocol or session, the
routes are tagged as external routes. Let's look at a simple example of a rout-
ing table that has external routes:

Router#show ip route eigrp

172.16.0.0/16 is variably subnetted, 301 subnets, 10 masks

D EX 172.16.27.230/32

[170/24827392] via 172.16.131.82, 11:39:32, ATM6/0/0.3114

D EX 172.16.237.16/29

[170/40542208] via 172.16.131.82, 11:41:32, ATM6/0/0.3114

[170/40542208] via 172.16.131.74, 11:41:32, ATM6/0/0.3113

D EX 172.16.237.24/29

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