IGRP Facts

Interior Gateway Routing Protocol (IGRP) is a dynamic routing protocol that sends neighboring routers updates of its routing table. It is Cisco's proprietary routing protocol, which Cisco recommends that you use instead of RIP. IGRP has the following characteristics:

IGRP can handle much larger networks, with

a hop count limit of 255 (rather than 16).

You can also configure the hop count limit.

IGRP uses a composite metric (a 24-bit number

assigned to each path that can include such

factors as bandwidth, delay, reliability,

loading, and MTU).

IGRP supports multiple-path connections.

It will keep track of same-cost and different-cost

routes. It can keep track of up to six different

paths.

IGRP uses flash updates (sending changed

information immediately) for faster convergence.

IGRP uses an autonomous system (AS) number

as part of the configuration.

IGRP uses split horizon with poison reverse.

The default update interval is higher for

IGRP than RIP because it uses flash updates.

Defaults are:

Update interval = 90 seconds

Invalid route = 270 seconds (3 times the

update)

Holddown = 280 seconds (3 times the update

+ 10)

Flush = 630 seconds (7 times the update)