What command is used to display the OSPF database on a router?

The command used to display the OSPF database on a router is "show ip ospf database." This command provides detailed information about all the OSPF routes that the router is aware of, including information on link-state advertisements (LSAs) and their types. The OSPF database contains essential information that allows the router to make routing decisions based on the current network topology.

Using "show ip ospf database," you can verify the OSPF configurations, understand the state of OSPF neighbors, and troubleshoot OSPF-related issues by assessing the contents of the database. It is an indispensable tool for network administrators managing OSPF environments, as it allows them to visualize the network structure and link states that OSPF is using to build its routing table.

In contrast, other commands listed do not specifically target the OSPF database. For example, "show ip route" displays the entire routing table, which includes all routing protocols but does not focus exclusively on OSPF details. "Show running-config" shows the router's configuration settings without detail on OSPF routes, while "show protocols" provides a summary of all of the configured protocols but does not specifically target OSPF's database contents.