IGRP routes

IGRP routes

7.3.3 This page will introduce the three types of routes that IGRP advertises:

• Interior

• System

• Exterior

Interior

Interior routes are routes between subnets of a network attached to a router interface. If the network attached to a router is not subnetted, IGRP does not advertise interior routes.

System

System routes are routes to networks within an autonomous system. The Cisco IOS software derives system routes from directly connected network interfaces and system route information provided by other IGRP routers or access servers. System routes do not include subnet information.

Exterior

Exterior routes are routes to networks outside the autonomous system that are considered when a gateway of last resort is identified. The Cisco IOS software chooses a gateway of last resort from the list of exterior routes that IGRP provides. The software uses the gateway of last resort if a better route is not found and the destination is not a connected network. If the autonomous system has more than one connection to an external network, different routers can choose different exterior routers as the gateway of last resort.

The Interactive Media Activity will help students understand the different types of IGRP routes.

The next page will introduce three features that increase the stability of IGRP.