An OSPF neighbor state is a stage in which two OSPF routers verify compatible settings and establish a relationship for exchanging routing information. The process begins when an OSPF-enabled interface sends hello messages and progresses from Down through Full. section 18.3.1 section 18.5
Know the state sequence and its practical meaning:
- Down means no hello has been received; Init means a hello arrived but did not list the local router ID. section 18.3.1
- ExStart, Exchange, Loading, and Full complete the progression toward exchanging routing information and establishing a full adjacency. section 18.5
Checking a neighbor
On R2, show ip ospf neighbor displays R1 as INIT/DROTHER, confirming that R2 received an OSPF hello but has not yet reached two-way recognition. R1’s corresponding output shows 2WAY/DROTHER.
