During which state does OSPF determine master and slave roles?

In the Open Shortest Path First (OSPF) protocol, the Exstart state is crucial because it is the phase where routers determine their roles as either master or slave during the process of establishing a neighbor relationship. This occurs after the Down and Init states and is fundamental to the OSPF adjacency formation process.

During the Exstart state, the two routers exchanging OSPF information decide who will be the master and who will be the slave based on their Router IDs. The router with the highest Router ID assumes the master role, which will then control the sequence of the Link State Advertisements (LSAs). This master-slave relationship is essential because it helps manage the flow of data between the routers and prevents any collisions that might occur if both attempted to send information at the same time.

The Init state is primarily for acknowledging the presence of neighbor routers, and the Down state indicates that there is no adjacency. The Exchange state follows Exstart and is where the actual database description packets are sent to convey the OSPF routing information, but by this time, the roles have already been established. Thus, the Exstart state is where the critical decision regarding master and slave roles takes place.