through the network. We also learned how routing protocols are used to
exchange IP address information between routers in an enterprise network.
IP addressing schemes establish a hierarchy that makes path information
both distinct and efficient. A router receives this routing information via a
given interface. It then advertises the information it knows out the other
physical interfaces. This routing process occurs at Layer 3 of the OSI model.
In this chapter, in order to decide on the best routing protocol or protocols to
use, we'll take a look at both the Interior Gateway Routing Protocol
(IGRP) and its big brother, the Enhanced Interior Gateway Routing Pro-
tocol (EIGRP).
tion and Core layer switches. (I need to note here that Cisco has licensed
IGRP to be used on other vendors' equipment, such as Compaq.) Each of
these routing protocols also has its own identifiable functions, so we'll dis-
cuss each routing protocol's features and differences. Once you understand
how these protocols differ from OSPF and how they calculate routes, you
will learn how to configure these protocols and fine-tune them with config-
uration changes to make each perform at peak efficiency.