no interfaces will have routing updates sent on them, and any routing updates received on the in- terfaces will be ignored. To enable interfaces in a routing protocol, specify the networks that are configured on the interfaces you wish to include by using the network command in router configura- tion mode: Router-A (config)#router rip Router-A (config-router)# network 10.10.10.0 With a classful protocol like RIP, you must be careful, because, as an example, including the network 10.0.0.0 will include every interface configured with a 10.x.x.x IP address, regardless of subnet mask. RIP does not allow the inclusion of a subnet or inverse mask in the network statements. You can enter a network other than 10.0.0.0, but IOS will convert the entry into the full classful network. The preceding entry results in the following being displayed in the configuration: router rip network 10.0.0.0 The configuration that would include all interfaces for Router A as shown in Fig- ure 10-10 is as follows: router rip version 1network 10.0.0.0 network 192.168.1.0 network 192.168.2.0 10.10.10.0/24 192.168.1.0/24 192.168.2.0/24 Router A 10.20.20.0/24 Figure 10-10. Routing protocol network interfaces One entry covers both the 10.10.10.0 and 10.20.20.0 networks, but the 192.168 net- works each require their own network statements. This is because 192.x.x.x networks are class C networks, while 10.x.x.x networks are class A networks. You won't always want to include every interface that the network statement encom- passes. In the preceding example, we might want to allow RIP on E0/0, but not on Specific Routing Protocols E1/1. This can be accomplished with the use of the passive-interface command, which removes an interface from the broader range specified by the network command: router rip version 1 passive-interface Ethernet1/1 network 10.0.0.0 The passive-interface command causes RIP to stop sending updates on the specified interface. The router will continue to receive and process RIP updates received on the interface, though. Routes l