Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA type is an external link advertisement generated by ASBRs?

1. Type 3

2. Type 4

3. Type 5

4. Type 7

The correct answer is: Type 5

The correct answer is that Type 5 Link State Advertisements (LSAs) are used for external link advertisements generated by Autonomous System Boundary Routers (ASBRs). In the context of OSPF (Open Shortest Path First), LSAs are critical for sharing routing information within and between different areas. Type 5 LSAs specifically denote routes that exist outside of the OSPF domain, informing OSPF routers about external networks that can be reached through ASBRs. ASBRs are responsible for redistributing routes from other routing protocols or from static routes into the OSPF routing table. By using Type 5 LSAs, they convey this information to other OSPF routers within the network. This allows OSPF to maintain a complete view of how to route packets towards networks that are not part of the OSPF protocol. Other LSA types serve different purposes. For example, Type 3 LSAs are used for inter-area routing, providing a means to summarize routes between OSPF areas. Type 4 LSAs are used to inform routers about the ASBR's location in relation to other OSPF routers. Type 7 LSAs are specific to Not-So-Stubby Areas (