My Experience: OSPF Adjacency Not Forming

 A few months ago, I was helping a client stabilize their WAN links between two branch offices. Everything looked fine on paper—interfaces were up, IPs were correct, and OSPF was enabled. Yet, the routers refused to form adjacency. No routes were being exchanged, and the network felt like two ships passing in the night.

🔍 Diagnosis

I started with the basics:

• show ip ospf neighbor returned nothing—no neighbors detected.
• show ip ospf interface confirmed that OSPF was active on the correct interfaces.
• ping and traceroute showed that Layer 3 connectivity was intact.

Then I dug deeper and found the culprit: mismatched OSPF Area IDs and hello/dead timers between the routers. One router was configured with Area 0, the other with Area 1. Additionally, the hello/dead timers didn’t match, which silently blocked adjacency.

✅ Solution

Here’s what I did:

1. Unified the Area ID:

router ospf 1 network 192.168.10.0 0.0.0.255 area 0

1. I ensured both routers were in Area 0.
2. Matched Hello/Dead Timers:

interface GigabitEthernet0/1 ip ospf hello-interval 10 ip ospf dead-interval 40

3. Cleared OSPF Process:

clear ip ospf process

2. This reset the OSPF state and allowed a fresh adjacency attempt.

Within seconds, show ip ospf neighbor showed both routers had formed a full adjacency. Routes began populating the routing table, and connectivity was restored.

📚 Reference That Helped

The Cisco Troubleshooting Guide was invaluable. It walked me through the use of show and debug commands, and helped me pinpoint the issue with OSPF parameters. I also leaned on this routing protocol troubleshooting breakdown, which explained how mismatches in OSPF settings can silently break communication.

This kind of issue is incredibly common—especially in environments where multiple admins touch configurations or when routers are added without full protocol alignment. It’s a reminder that even small mismatches can cause big disruptions.