OSPF Neighbor States Changing on 'debug ip ospf adj'

debug ip ospf adj is used to troubleshoot neighbor adjacency issues of OSPF. It lists all the state changes a router go through when forming a neighbor relationship.

As a summary it should go through the following states.

1. Down: no OSPF neighbors detected at this moment.
2. Init: Hello packet received.
3. Two-way: own router ID found in received hello packet.
4. ExStart: master and slave roles determined.
5. Exchange: database description packets (DBD) are sent.
6. Loading: exchange of LSRs (Link state request) and LSUs (Link state update) packets.
7. Full: OSPF routers now have an adjacency.

Let's see how it is displayed on a router. Only two routers are connected for this lab with a direct cable and following configuration is applied to both routers. Note that the link is a multi access segment with a /24 subnet.

Router(config)#router ospf 100
Router(config-router)#network 192.168.12.0 0.0.0.255 area 0

R1's interface is 192.168.12.1/24 and R2's interface is 192.168.12.2/24
R1's loopback is 1.1.1.1/32 and R2's loopback is 2.2.2.2/32

(click on the images to view in full size)