1.4 Routing Protocol
1.4.10 IGRP configuration example
In the example:

router igrp 109 -- Selects IGRP as the routing protocol for autonomous system 109. 
network 1.0.0.0 -- Specifies a directly connected network. 
network 2.0.0.0 -- Specifies a directly connected network.

IGRP is selected as the routing protocol for autonomous system 109. All interfaces connected to networks 1.0.0.0 and 2.0.0.0 will use IGRP to gather and distribute routing information.