What is the preferred command to make a newly modified router ID effective on an OSPF router?

The preferred command to make a newly modified router ID effective on an OSPF router is "clear ip ospf process." When you change the router ID in OSPF, the OSPF process must be reset for the new router ID to take effect. By using this command, the OSPF process is cleared and restarted, which allows the new router ID to be recognized and utilized in the OSPF network.

This command does not require a complete router reboot, making it a more efficient option compared to reloading the router. Additionally, other commands such as "shutdown" or "exit" do not directly apply to adjusting OSPF parameters like the router ID. "Shutdown" could halt OSPF without addressing the router ID change, and "exit" simply terminates the current command mode without impacting the OSPF configuration. Therefore, "clear ip ospf process" is the most effective and preferred command to ensure the updated router ID is operational.