Cisco ENCOR Practice Exam 2025 – All-in-One Comprehensive Guide to Mastering Enterprise Network Core Technologies!

Area filtering in OSPF (Open Shortest Path First) is primarily implemented using a prefix filter list at the Area Border Router (ABR). The ABR serves as a boundary between different OSPF areas and can control the flow of routing information between these areas.

By utilizing prefix lists, the ABR can selectively permit or deny specific routes from being advertised between areas. This allows for controlling which routes are shared and preventing unnecessary or undesired routes from being flooded into particular OSPF areas, thus managing the overall routing information exchanged.

LSA flooding is a normal part of OSPF's operation where Link State Advertisements are propagated to ensure all routers have a synchronized view of the network topology. However, this process does not inherently provide the ability to filter areas.

Route maps can be used in conjunction with prefix lists to enhance routing policies, but the fundamental implementation of area filtering would be through the prefix filter list itself.

Defining area types, such as stub or not-so-stubby areas, alters routing behavior and influences route advertisement but does not specifically relate to filtering based on prefixes. Instead, these types indicate how external routes are handled within an area.

Thus, using a prefix filter list at the ABR is the correct answer for