Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA Type is generated by OSPF routers to describe the state of their local interfaces?

1. Type 1 LSA (Router LSA)

2. Type 2 LSA (Network LSA)

3. Type 3 LSA (Inter-Area Prefix LSA)

4. Type 5 LSA (AS External LSA)

The correct answer is: Type 1 LSA (Router LSA)

The Type 1 LSA, also known as the Router LSA, is generated by OSPF routers to convey information about the state of their local interfaces. This LSA type contains details about the router’s interfaces, including their IP addresses, associated subnet masks, and the OSPF cost of routing to those interfaces. It is crucial as it helps to build a complete picture of the router's capabilities and how it connects to other routers within the same OSPF area. Type 1 LSAs are flooded within the OSPF area and are used to share routing information about the local router itself. They contribute to the OSPF link-state database, which all routers use to compute the shortest path to destinations using the Dijkstra algorithm. In contrast, other LSA types serve different purposes such as Type 2 LSAs, which describe networks shared by multiple routers, Type 3 LSAs that summarize routes between different areas, and Type 5 LSAs which are used to describe external routes originating from outside the OSPF autonomous system. Each LSA type has its unique function in the OSPF protocol, reflecting the structured approach OSPF uses to manage and disseminate routing information.