OSPF Peering Process

 ✅ 1. Verify OSPF Process Is Running

show ip protocols
show ip ospf

• Ensure OSPF is enabled.
• Correct process ID and routing information present.

✅ 2. Check OSPF Interface Participation

show ip ospf interface brief

• Interface must be in the right area.
• Roles should be DR, BDR, or DROTHER.

✅ 3. Verify Interface IP and Subnet

show ip interface brief
show run interface <interface>

• Both routers should be in the same subnet.
• Interface must be up and not shutdown.

✅ 4. Check OSPF Hello and Dead Timers

show ip ospf interface <interface>

• Hello & Dead timers must match.
• Default: Hello = 10s, Dead = 40s

✅ 5. Check OSPF Network Type

show ip ospf interface <interface>

• Must match on both sides:
• broadcast, point-to-point, or non-broadcast

interface <interface>
ip ospf network <broadcast | point-to-point | non-br

✅ 6. Check for Passive Interface

show run | section router ospf

• Passive interfaces won’t form neighbors.

router ospf <process-id>
no passive-interface <interface>

✅ 7. Check OSPF Authentication

show ip ospf interface <interface>

• Both routers must use:
• Same authentication type (None, Simple, MD5)
• Same password

interface <interface>
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 <password>

router ospf <process-id>
area <area-id> authentication message-digest

✅ 8. Clear OSPF Neighbor Relationships (if needed)

clear ip ospf process
clear ip ospf neighbor <neighbor-ip>

✅ 9. Verify OSPF Neighbor State

show ip ospf neighbor

• Desired state: FULL

✅ 10. Check Logs for Clues

show log

Look for:
• Interface flaps
• Timer mismatches
• Area mismatches

✅ 11. Check for Duplicate Router IDs

show ip ospf

• Router IDs must be unique within the OSPF domain.

✅ 12. Check for MTU Mismatch

show interface <interface> | include MTU

• MTU mismatch can cause stuck state at EXSTART/EXCHANGE.

✅ 13. Verify Stub Area Configuration

show ip ospf

• Both routers must agree on stub/NSSA settings.

✅ 14. Check Access Lists or Firewalls

show ip access-lists
show running-config | include access-group

• Ensure no ACL or firewall blocks OSPF protocol 89.

✅ 15. Final Verification

show ip ospf neighbor
show ip ospf interface
ping <neighbor-ip>

• Confirm OSPF peering is established and stable.