Which command is used for configuring OSPF on a router?

The configuration of OSPF (Open Shortest Path First) on a router is accomplished using the command "router ospf [process-id]." This command is essential because it enters OSPF configuration mode, allowing the network administrator to specify parameters related to OSPF, such as router ID, network statements, and other OSPF settings.

When issuing this command, the [process-id] is a numerical identifier that helps distinguish between multiple OSPF processes running on the same router. Each OSPF instance operates independently, so it is crucial to specify the correct process ID when configuring the protocol to ensure that the desired OSPF instance is modified.

In contrast, the other options do not accurately represent the command structure used in OSPF configuration. For instance, "enable ospf" and "set ospf" are not valid commands in the context of OSPF configuration, and "config ospf" does not follow the correct syntax and structure that a network administrator needs to utilize when setting up OSPF effectively on a router. Therefore, the command "router ospf [process-id]" is the only correct option for entering the OSPF configuration mode on a router.