Cisco Certified Network Associate (CCNA) Practice Exam

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What type of OSPF area blocks Type 5 LSA types but allows Type 3 and 4?

Backbone area
Normal area
Stub area
Totally stubby area

The correct answer is: Stub area

A stub area is designed to optimize OSPF operations by blocking certain types of links and reducing the amount of routing information that routers in the area must process. Specifically, a stub area blocks Type 5 LSAs, which are used to advertise external routes (from other routing protocols), but it permits the propagation of inter-area routes, which are carried by Type 3 LSAs. Additionally, Type 4 LSAs, which provide information about the ASBR (Autonomous System Boundary Router) used to reach external networks, are also allowed in a stub area. By restricting the types of LSAs, stub areas help conserve bandwidth and memory on routers, simplifying the OSPF routing table and providing a more efficient routing environment. This is critical for reducing routing updates and minimizing processing requirements on devices within the stub area while still allowing them to receive essential routing information from other areas.