What type of OSPF messages are exchanged during the adjacency formation process?

In the OSPF adjacency formation process, the Database Description (DBD) messages play a critical role. During this phase, routers exchange their DBD messages after initially establishing a hello adjacency. These messages contain summaries of the link-state information that each router possesses, which helps them determine the state of their databases and the need for additional information.

The purpose of exchanging DBD messages is to check for consistency between neighboring routers. Each router uses the DBD to describe which link-state advertisements (LSAs) are already known, thus allowing routers to efficiently synchronize their link-state databases. This mechanism is essential for maintaining an accurate and updated view of the network topology.

In contrast, the other message types serve different functions within OSPF. Link-State Update (LSU) messages are used for the distribution of new link-state information but are sent after adjacency has been established. Link-State Requests (LSR) are sent to request specific LSAs that a router needs, typically following the DBD message exchange process. Finally, Link-State Acknowledgments (LSAck) confirm the receipt of LSUs but also occur after the DBD phase. Therefore, while all these message types are important in OSPF operations, the DBD messages are specifically critical