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Chapter 10

Route Optimization

you. You need to remember that even though the router will fix it for you,
the Cisco certification exam will not, and you will get a wrong answer. Just
remember that a classful routing protocol is always configured with all sub-
net and host bits off.

Another thought to keep in mind regarding RIP version 1 is that it doesn't

work with VLSM because subnet mask information is not sent with the route
updates. Since RIP version 2 does send prefix information, you absolutely
must use RIP version 2 if you are trying to perform any type of VLSM
networking.

OSPF

SPF (Open Shortest Path First) uses an algorithm to determine a

composite metric. Specifically, the algorithm used is based on the Dijkstra
Algorithm, named after its inventor, Edsger Dijkstra. This algorithm uses
only the bandwidth of a link to determine the cost to a remote network.
Remember that OSPF does not summarize by default like IGRP, EIGRP, and
RIP. However, unlike RIP, OSPF is a classless routing protocol, which means
that it includes subnet information (prefix information) in its routing
updates. OSPF is typically the fastest converging routing protocol for IP.
However, we have found that EIGRP can give it a run for the money in
smaller networks in regards to convergence times.

IGRP

GRP (Internet Gateway Routing Protocol) is a Cisco proprietary pro-

tocol and therefore cannot run on routers from other vendors. Similar to
RIP, IGRP is a classful, distance-vector protocol. However, IGRP uses a
much more complex metric than RIP. Specifically, the metric for IGRP is
made up of the following five components:

Bandwidth The bandwidth value is represented by the number of Kbps
that a particular interface is capable of. For example, a 10Mbps Ethernet
port would, by default, have a bandwidth value of 10,000 (10,000Kbps
= 10Mbps). Similarly, a 56Kbps serial interface would have a bandwidth
value of 56. All Cisco routers have a default bandwidth of 1.544Mbps on

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