What is the first state in the OSPF neighbor state sequence?

In the OSPF (Open Shortest Path First) protocol, the first state in the neighbor state sequence is the Down state. This state indicates that no hello packets have been received from a neighbor router yet, and thus there is no established communication. It represents the starting point for establishing an OSPF adjacency.

Once the OSPF process begins, the router will stay in the Down state until it detects the presence of a neighbor by receiving hello packets. From there, the OSPF neighbor state can transition through other states, such as Init, which indicates that the router has received hello packets but has not yet fully established a neighbor relationship. Understanding this sequence is essential for network troubleshooting and ensuring that OSPF operates correctly within a network environment.

The subsequent states, such as Loading and Full, represent further stages in the adjacency formation process, with Full being the state in which both routers have completed the handshake and can exchange routing information. Verifying the transition from Down to the other states is crucial in network diagnostics when checking OSPF neighbor relationships.