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Chapter 10

Route Optimization

Advanced Redistribution

ur redistribution examples up to this point have set the default met-

ric for a particular routing protocol. That metric is then used every time
another routing protocol is redistributed into that particular routing proto-
col. Also, in our examples, all the routes have been redistributed; that is, we
have not been filtering the content of our routing updates.

We will now examine how to control redistribution with a higher degree

of granularity. For example, we may want RIP to apply one metric to OSPF
and another metric to IGRP, as these products are redistributed into the RIP
routing process.

Also, in some cases, we may want only a subset of routes redistributed.

When, in our example, the two companies merge, perhaps we don't want the
users on Network B to be able to access the services on network 2.0.0.0 in
Network A, for security reasons. In other instances, we may not want to
advertise or accept advertisements from all available routes, due to the sheer
volume of routes. For example, if our router is connected to an Internet Ser-
vice Provider and is accepting full routes from the Internet, we would have
over 65,000 routing entries in our routing table. Such a large number of
routing entries consumes a significant amount of RAM and processor
overhead.

Protocol-Specific Metrics

Let's examine how to set up redistribution such that we set the metric for a
redistributed protocol as part of the redistribute command. To illustrate,
let's consider the first example given in the chapter, where Network A is run-
ning EIGRP and Network B is running RIP. Figure 10.7 shows how we could
configure RouterB to accomplish route redistribution. This syntax gives us
the flexibility to specify alternate metrics for EIGRP and RIP to use if other
routing protocols, such as OSPF, were being redistributed into them.

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