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Chapter 10
Route Optimization
F I G U R E 1 0 . 3
Improper redistribution
The solution to this problem of mixed routing protocols is route redistri-
bution. The reason that route redistribution does not happen automatically
between diverse routing protocols is that the protocols have different meth-
ods of representing the desirability of a route. This desirability is called a
metric. Also, some routing protocols include subnet information (prefix
information) within routing updates (e.g., classless routing protocols), and
some routing protocols do not include subnet information (e.g., classful
routing protocols). Therefore, to better understand how we redistribute one
routing protocol into another, let's first review some characteristics of vari-
ous routing protocols.
Routing Protocol Metrics
In this section, we will discuss the various routing protocols and metrics used
to calculate the best path to all remote networks. It is important to remember
that a router first used the administrative distance as a tool to find the best
path to a remote network. For example, if you have a network route being
advertised to a router with both RIP and IGRP, the IGRP route will be used
and the RIP route will be ignored. If two or more routes are being advertised
as available routes to the remote network, then the metric of a routing pro-
tocol is used to determine the best path. If the metrics are the same, the routing
Network B
router eigrp 10
router rip
Network A
EIGRP - Process ID 10
I cannot see
from RouterC.
I can see routes
both from RouterA
and RouterC.
I cannot see
from RouterA.
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