Cisco Certified Network Associate (CCNA) Practice Exam

What does a Type 1 LSA describe in OSPF?

1. Routes to external networks

2. Directly connected networks

3. Summary routes

4. Multi-access network identification

The correct answer is: Directly connected networks

A Type 1 LSA, or Link State Advertisement, in OSPF (Open Shortest Path First) specifically describes directly connected networks within an OSPF router's local area. When a router generates a Type 1 LSA, it advertises its interfaces and the networks that are directly attached to it, forming what is known as the router's link-state. This allows other routers in the area to gain an accurate representation of the links within the OSPF domain and understand how to route packets effectively. Type 1 LSAs are crucial in OSPF operation because they ensure that all routers within an OSPF area have synchronized view of the network topology, which is essential for the formation of the link-state database (LSDB). This database is used by OSPF to calculate the shortest path to each destination network, enabling efficient and reliable routing. In contrast, other types of LSAs serve different purposes. For example, Type 2 LSAs describe network segments (essentially multi-access networks) and the routers attached to them, while Type 5 LSAs indicate routes to external networks. Therefore, the focus of a Type 1 LSA remains strictly on the directly connected networks of a single router, making it foundational