In which OSPF state does a router send out link-state advertisements?

In OSPF, the Two-way state is the stage where routers establish a neighbor relationship and recognize each other. When a router reaches the Two-way state, it has successfully exchanged Hello packets with its neighbor and made sure that both routers are able to communicate.

During this state, routers send and receive link-state advertisements (LSAs) to inform each other about their link states. This is crucial for the formation of the OSPF topology across the network and for ensuring that all routers have the most up-to-date information about the network's structure. It marks the beginning of the process where routers collect and share information about their connected links, which ultimately leads to the creation of a reliable routing table.

Other stages, such as the Full state, indicate that the routers have completed the LSA exchange and are fully synchronized, while the Exchange and Loading states involve the actual transmission of information but do not establish the initial conditions for LSAs like the Two-way state does. Thus, recognizing the Two-way state as the point at which link-state advertisements are sent is fundamental to understanding OSPF operation and neighbor relationships.