Idea of Interior Gateway Routing Protocol [ IGRP ]



Interior Gateway Routing Protocol (IGRP) is a Cisco proprietary distance-vector routing protocol. This means that all your routers must be Cisco routers to use IGRP in your network. Cisco created this routing protocol to overcome the problems associated with RIP. IGRP has a maximum hop count of 255 with a default of 100. This is helpful in larger networks and solves the problem of there being only 15 hops maximum possible in a RIP network. IGRP also uses a different metric form RIP. IGRP uses bandwidth and delay of the line by default as a metric

for determining the best route to an internetwork. This is called a compositmetric. Reliability, load, and Maximum Transmission Unit (MTU) can also be used, although they are not used by default.

IGRP Timers

To control performance, IGRP includes the following timers with default settings:

Update timers

These specify how frequently routing-update messages should be sent. The default is 90 seconds.

Invalid timers

These specify how long a router should wait before declaring a route invalid if it doesn’t receive a specific update about it. The default is three times the update period.

Holddown timers

These specify the holddown period. The default is three times the update timer period plus 10 seconds.

Flush timers

These indicate how much time should pass before a route should be flushed from the routing table. The default is seven times the routing update period.

Configuring IGRP Routing

The command used to configure IGRP is the same as the one used to configure RIP routing with one important difference: you as an autonomous system (AS) number. All routers within an autonomous system must use the same AS number, or they will not communicate with routing information. Here is an example of how to turn on IGRP routing:

RouterA#config t

RouterA(config)#router igrp 10


We have make this kind of configure in every router where we want to use RIP as a routing (15 router max).

Verifying our Configurations:

It is important to verify your configurations once you have completed them, or at least, once you think you have completed them. The following list includes the commands you can use to verify the routed and routing protocols configured on your Cisco routers. The first command is covered in the previous section; the others are covered in upcoming sections.

-show ip route

-show protocol

-show ip protocol

-debug ip rip

-debug  ip igrp events

-debug ip igrp transactions

                                            ———————– Thanks everyone


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