How do you enable HSRP preemption on a router interface?

To enable Hot Standby Router Protocol (HSRP) preemption on a router interface, the correct command is "standby group-number preempt." This command allows a router that has a higher priority value to take over the active role from the current active router in the HSRP group when it becomes available.

In HSRP, preemption is important because it ensures that the router with the highest priority is always the one actively forwarding packets, thus providing better redundancy and failover capabilities. When a higher-priority router comes online, it can take back the role of the active router if preemption is enabled.

The correct order of the command is crucial: "standby" identifies it as an HSRP command, followed by the specific group number in which preemption should occur, and "preempt" indicates the action of allowing preemption to happen. This order is significant because Cisco's command-line interface is structured to interpret commands in a specific format.

The other options do not follow this correct syntax of HSRP commands, which is why they are not valid for enabling preemption. Understanding the correct command structure is essential for effective network configuration and management.