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Chapter 6
IGRP and EIGRP
which differ among specific routing protocols and can range from 30 min-
utes to two hours.
These are key differences that permit link-state routing protocols to func-
tion well in large networks--they really have no limitations when it comes to
scaling, other than the fact that they're a bit more complex to configure than
distance-vector protocols.
Interior Gateway Routing Protocol
I
nterior Gateway Routing Protocol (IGRP) is a Cisco proprietary rout-
ing protocol that uses a distance-vector algorithm. It uses this algorithm
because it uses a vector (a one-dimensional array) of information to calculate
the best path. This vector consists of four elements:
Bandwidth
Delay
Load
Reliability
We'll describe each element in detail shortly.
Maximum transfer unit (MTU) information is included in the final route infor-
mation, but it's used as part of the vector of metrics.
IGRP is intended to replace RIP and create a stable, quickly converging
protocol that will scale with increased network growth. As we mentioned,
it's preferable to implement a link-state routing protocol in large networks
because of the overhead and delay that results from using a distance-vector
protocol.
In the next few sections, we will quickly take you through the features of
IGRP and show how to implement this routing protocol in your network.
We will also cover the types of metrics, unequal-cost load balancing, and the
limitations of redistribution.
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