Cisco Certified Network Associate (CCNA) Practice Exam

Which LSA is responsible for advertising external routes in OSPFv3?

1. Type 1 LSA (Router LSA)

2. Type 2 LSA (Network LSA)

3. Type 5 LSA (AS External LSA)

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

The correct answer is: Type 5 LSA (AS External LSA)

In OSPFv3, Type 5 LSA, also known as the AS External LSA, is responsible for advertising external routes. This LSA type is critical for OSPF to communicate routing information learned from external sources, such as routes from other routing protocols or static routes, to other OSPF routers within the area. The AS External LSA provides the necessary information about routes that are external to the OSPF autonomous system and allows OSPF to maintain a complete view of the network, including paths to destinations that are outside of its own OSPF domain. This is particularly important for ensuring that OSPF can make informed routing decisions and maintain network connectivity by integrating external routes into its topology maps. Other types of LSAs perform different functions within OSPF. For example, Type 1 LSAs (Router LSAs) describe the state and cost of the router's interfaces to the router itself, while Type 2 LSAs (Network LSAs) represent the multi-access networks and the routers connected to them. Type 3 LSAs (Inter-Area Prefix LSAs) are used for advertising inter-area routes but do not deal with external routes. Understanding the specific roles of each LSA type is essential