OSPF Neighbor Not Showing In show ip ospf neighbor Command

Issue Description: Troubleshoot OSPF Adjacency

If the “show ip ospf neighbor” command reveals nothing at all – or reveals nothing about the particular neighbor you are analyzing – then this router has not seen any “valid” OSPF HELLOs from that neighbor. This means that OSPF either did not receive any HELLO packets from the neighbor or received HELLO packets that failed.

Troubleshooting steps:

Check if the interface on the local router and neighboring router are up: use commande show interface and show ip interface brief.
Check the IP connectivity between the local and remote OSPF neighbor router: use ping or traceroute to check if takes more than 1 hop to the destination (should be 1 single hop).
Check if the neighbor respond if you enter a ping 224.0.0.5 command (Hello Multicast address).
Check for any inbound access lists or other devices (such as a switch) that can deny the sending of IP packets from one neighbor to the other.
Check if OSPF enabled on both local interfaces and the interface of the neighboring router: use show ip ospf interface to check.
Verify that the Interface is Active OSPF not passive: use show ip ospf interface and verify Hello Packets to be sent ( an active Interface should show line like “Hello due in 00:00:04“, which means that still 4 seconds until sending the next Hello packet).
Check that neighboring routers have different Router IDs from local OSPF router. Router IDs are used in order to identify each router in an OSPF network.
Routers with the same Router ID will ignore HELLOs sent by each other, which prevents them from forming adjacency.
Check that All OSPF Neighborship conditions and matching requirements are verified (Area Id and type, Timers..
Please refer to this article about Neighborship conditions and matching requirements.