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Chapter 10
Route Optimization
If you were to look at a network analyzer, you would see that IGRP sends
route updates with all the metric information described above. However, by
default, IGRP routing protocols use only bandwidth and delay of the line to
determine the best route. MTU, reliability, and load have to be configured by
the administrator. I don't recommend this unless it is a rainy Saturday and
you have absolutely nothing else to do in the world and you want to amaze
your friends at work on Monday morning.
IGRP (Enhanced IGRP) is a Cisco proprietary protocol, like IGRP.
The good news is that EIGRP uses the same metric components as IGRP
(bandwidth, delay, reliability, load, and MTU size) but also uses only band-
width and delay of the line by default as IGRP does. The news gets even bet-
ter. Since EIGRP and IGRP use the same metrics, they can automatically be
redistributed into each other, provided that they are using the same autono-
mous system number. Later we'll present an example that will clarify this
automatic redistribution. Unlike IGRP, however, EIGRP is a classless rout-
ing protocol. Therefore, EIGRP is capable of sending subnet information in
its routing updates.
Configuring Route Redistribution
ow that we have an understanding of the issues involved in route
redistribution (metrics and classless versus classful), we will examine some
basic scenarios of route redistribution. Let's first consider the situation pre-
sented at the beginning of the chapter--two companies merging and needing
to redistribute RIP and EIGRP into each other.
As you already know, we have two networks that are merging together.
RouterB's routing table knows the routes from both RouterA and RouterC,
because it is configured to run both the RIP and EIGRP routing processes.
However, RouterA and RouterC cannot see the routes from each other, as
shown in Figure 10.4.
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