Cisco Certified Network Associate (CCNA) Practice Exam

Which of the following LSA types is used to summarize routes to an ASBR?

1. Type 4: Summary LSA

2. Type 3: Summary LSA

3. Type 1: Router LSA

4. Type 2: Network LSA

The correct answer is: Type 4: Summary LSA

The correct choice involves understanding the function of different Link State Advertisements (LSAs) in an OSPF (Open Shortest Path First) network. The Type 4 LSA, known as the Summary LSA, is specifically used to advertise the presence of an Autonomous System Boundary Router (ASBR) to other areas within an OSPF domain. When an ASBR is located within an OSPF area, the Type 4 LSA allows for the summarization of routes that lead to that ASBR, helping in route optimization and reducing the size of the routing table. This summarization capability is critical for efficient routing within large OSPF networks, as it consolidates routes and facilitates the distribution of external routes injected into the OSPF network by the ASBR. By summarizing the routes to the ASBR, the Type 4 LSA enables other areas to understand how to reach external destinations without overwhelming them with detailed routing information. The other types of LSAs serve different purposes. For instance, Type 3 LSAs are used to summarize inter-area routes but do not specifically target ASBRs. Type 1 LSAs are generated by routers to advertise their own interfaces and the directly connected networks, while Type 2