To enter RIP configuration mode, which command should be used?

The command to enter RIP configuration mode is "router rip." When configuring routing protocols in Cisco devices, you need to specify which protocol you want to configure, and in this case, "router rip" is the correct entry point that allows you to begin configuring the Routing Information Protocol (RIP).

Entering this command places you into the router configuration mode specifically for RIP, where you can define various parameters related to routing, such as specifying the networks that will participate in RIP, setting timers, and configuring additional features.

The other options do not correctly initiate RIP configuration mode. For instance, "config rip" and "rip configure" are not valid commands in the Cisco IOS for entering RIP configuration, and "network rip" is not a command used to access the configuration mode but rather a command used within that mode to specify which networks to advertise.