EIGRP and wildcard masks

The network command in EIGRP uses a classful network as the parameter by default, which means that all interfaces inside the classful network will participate in the EIGRP process. We can enable EIGRP only for specific networks using wildcard masks. The syntax of the command is:

(router-eigrp)#network IP_ADDRESS WILDCARD_MASK

Consider the following example:

In the picture above you can see a network with three hosts and a router. The router is directly connected to three subnets. Let’s say that we want to advertise only the 10.0.0.0/24 subnet in EIGRP. We can use the wildcard mask of 0.0.0.255 to do this:

Using the show ip protocols command, we can verify that the network 10.0.0.0/24 is included in EIGRP: