Final answer:
The 'passive-interface interface#' command configures the specified interface as a passive routing interface, which prevents the router from sending routing updates but still allows receiving them.
Step-by-step explanation:
The command 'passive-interface interface#' is used in router configuration to configure the specified interface as a passive routing interface. When an interface is made passive, it means that the router will not send any routing updates out of that interface, but it will still receive routing updates on that interface. This is useful for security purposes, to reduce unnecessary traffic, and to prevent the advertising of routing information on segments where it's not needed. In essence, it doesn't deactivate the interface for routing updates; rather, it changes its behavior concerning how it deals with routing updates.