In which OSPF state do routers first exchange their link-state information?

In OSPF (Open Shortest Path First) routing, the D. Exchange state is where routers first begin to exchange their link-state information. During this state, routers that are in the process of establishing an OSPF adjacency, after reaching the 2-Way state, exchange link-state advertisements (LSAs) with each other. This exchange includes sending full LSA updates to one another, which allows them to learn about the network topology and the state of each neighboring router's links.

The importance of the Exchange state lies in its role in facilitating the sharing of vital routing information, which is crucial for the OSPF algorithm to build and maintain an accurate picture of the network. Once routers have completed this exchange, they transition to the Loading state, where they process and acknowledge received LSAs to ensure all routers have a synchronized view of the network.

Understanding these states is essential for grasping how OSPF operates, especially when troubleshooting OSPF-related issues or optimizing OSPF configurations in a network.