7.4 The 0.0.0.0 Default Route
7.4.3 Using 0.0.0.0 with IGRP
The only difference between the way IGRP uses 0.0.0.0 and the way RIP uses it is that IGRP does not advertise it, even if a redistribute static command and a default metric are configured. The solution for creating a local domain default route for IGRP is given in this scenario. The 0.0.0.0 route might be installed as a gateway of last resort by a router running IGRP, even though IGRP --- unlike RIP --- doesn't treat 0.0.0.0 any differently than any other route. This is because the IP functionality of the Cisco IOS software itself installs the route, not IGRP.

A router that has not yet been configured with a dynamic routing protocol still must be able to handle some basic IP functions. In fact, some routers use only static routes and connected routes to maintain the IP connectivity they require. These functions are built into the Cisco IOS software to ensure that they are available.

Lab Activity
  In this lab, you will learn how to use a default network with IGRP to setup a gateway of last resort on all IGRP routers.