How can you configure an OSPF Distribution-List Filter?

Configuring an OSPF distribution-list filter involves using an Access Control List (ACL) to specify which routes should be advertised or blocked within the OSPF protocol. The correct answer indicates that an ACL can be defined and then applied directly under the router OSPF configuration to filter routes.

When you define an ACL, it allows you to control the routing updates that OSPF will send to other routers. By applying this ACL in the OSPF configuration, you can manage which routes are included in OSPF advertisements, thereby refining the routing behavior based on your network requirements. The setup ensures that only the routes specified in the ACL are processed by OSPF, allowing for tailored route filtering that can enhance the efficiency and accuracy of routing information exchanged in the network.

The other options suggest various methods of manipulation that do not align directly with the OSPF configuration process for distributing lists. While ACLs can be implemented on routers in various capacities, option B specifically highlights the correct method of filtering routes within the OSPF context by applying the ACL directly in the OSPF configuration.