What are the types of link-state advertisements (LSAs) in OSPF?

The correct answer identifies that there are four distinct types of link-state advertisements (LSAs) used in Open Shortest Path First (OSPF), which include Router LSAs, Network LSAs, Summary LSAs, and AS-external LSAs.

Router LSAs are generated by all OSPF routers and provide information about the state of the router's interfaces and the links to its neighbors. They are essential for building the OSPF link-state database, as they convey local routing information.

Network LSAs are produced by designated routers on multi-access networks, such as Ethernet segments, and they summarize the routers that are present on that network. This helps in maintaining an efficient routing table and ensuring that all OSPF routers have the necessary information to compute the shortest path to each destination.

Summary LSAs come into play mainly between OSPF areas and are used to summarize routes from one area to another. This is particularly useful in reducing the amount of routing information that needs to be exchanged between areas, thereby optimizing performance.

AS-external LSAs are used to advertise routes to networks that are external to the OSPF autonomous system. This enables the OSPF domain to interact with other routing protocols and ensures that external routes can be included