Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA type is responsible for informing the OSPF domain about the ASBR?

1. Type 1

2. Type 4

3. Type 5

4. Type 2

The correct answer is: Type 4

The correct understanding involves the role of different LSA (Link-State Advertisement) types in OSPF (Open Shortest Path First) routing protocols. Type 4 LSAs specifically serve the purpose of identifying ASBRs (Autonomous System Boundary Routers) to other routers within an OSPF domain. When an OSPF network includes external routes learned from other routing protocols, the ASBR is responsible for injecting these routes into the OSPF domain. To inform other routers about its existence and capabilities to distribute these external routes, the ASBR generates Type 4 LSAs. This informs OSPF routers about how to reach the ASBR, which is crucial for ensuring that they can appropriately utilize the external routes being advertised. Other LSA types have distinct functions; for instance, Type 1 LSAs are used by routers to inform about their own connected networks within an area, Type 2 LSAs represent the multi-access networks (like Ethernet) and provide information about the routers connected to that segment, and Type 5 LSAs are used to advertise external routes originating from outside the OSPF domain. Understanding the specific roles of these LSA types helps clarify how OSPF manages routing information within complex networks.