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Troubleshooting IGRP
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Troubleshooting IGRP
I
GRP is a Cisco proprietary routing protocol that uses a distance vector
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
MTU, or maximum transmission unit, information is included in the final
route information, but it's not used as part of the vector of metrics. Each ele-
ment will be described in detail in a little while.
IGRP is intended to replace RIP and create a stable, quickly converging
protocol that scales with increased network growth. As mentioned, it's pref-
erable to implement a link-state protocol in large networks because of the
high overhead and delay that result from using a distance vector protocol.
IGRP has several features included in the algorithm--these features and a
brief description of each can be found in Table 6.5. These features were
added to make IGRP more stable, and a few were created to deal with rout-
ing updates and to make network convergence happen more quickly.
T A B L E 6 . 5
IGRP Features
Feature
Description
Configurable
metrics
Metrics (or variables in the equation) may be configured
by the user.
Flash updates
Updates are sent out prior to the default time setting.
Updates occur when the metrics for a route change.
Poison reverse
updates
These are implemented to prevent routing loops. The
updates place a route in holddown. (Holddown means
that the router won't accept any new route information
on a given route for a certain period of time.)
Unequal-cost
load balancing
This feature allows packets to be shared/distributed
across multiple paths.
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