Which type of LSA is used to advertise external routes in OSPF?

The correct choice is based on the function of different Link-State Advertisements (LSAs) used in Open Shortest Path First (OSPF). Type 5 LSAs are specifically designated for advertising external routes, which include routes that originate from outside the OSPF autonomous system. This is crucial for allowing OSPF to incorporate external network information into its routing decisions.

Type 5 LSAs contain information about routes to external networks, and they are flooded throughout the OSPF area to ensure that all OSPF routers have consistent information about the external networks they can reach. These LSAs are generated by ASBRs (Autonomous System Boundary Routers), which serve as the connection point between different routing protocols or different OSPF areas.

Other types of LSAs have different purposes; for instance, Type 2 LSAs are used for advertising network segments that are multi-access (like Ethernet) and generated by designated routers, while Type 3 LSAs are used to advertise inter-area routes within OSPF. Type 7 LSAs, on the other hand, are used in OSPF Not-So-Stubby Areas (NSSA) and serve a specific function that differs from the type of external route advertisement that Type