Step 1: Verify Basic Connectivity
✅ ping <neighbor IP> → Ensure devices can reach each other.
✅ show interfaces status → Check interface status (UP/Down).
✅ show ip arp → Verify correct MAC resolution.
Step 2: Check OSPF Neighbor Relationship
✅ show ip ospf neighbor → Check if neighbors are in Full state.
✅ debug ip ospf adj → Identify adjacency issues.
🔴 If neighbors are stuck in INIT or EXSTART:
- Check MTU mismatch →
show ip ospf interface - Check Hello/Dead timer mismatch →
show ip ospf interface - Check Network Type mismatch (Broadcast, P2P, etc.)
- Check Area ID mismatch →
show ip ospf interface brief - Check for authentication issues →
show running-config | section ospf
Step 3: Validate OSPF Route Advertisements
✅ show ip route ospf → Confirm OSPF routes are present.
✅ show ip ospf database → Verify LSAs are exchanged properly.
✅ debug ip ospf lsa → Check if LSAs are being received.
🔴 If missing routes:
- Check if the interface is passive →
show ip ospf interface brief - Check LSA filtering or stub area restrictions
- Check for route summarization issues
Step 4: Check OSPF Path Selection & Costs
✅ show ip ospf interface → Verify OSPF cost settings.
✅ show ip ospf database router → Inspect LSA details.
✅ show ip route <destination> → Check the chosen OSPF path.
🔴 If unexpected routes appear:
- OSPF cost may be too high/low → Adjust with
ip ospf cost <value> - Check for ECMP issues (Equal-Cost Multipath Routing)
Step 5: Verify External Route Redistribution (If applicable)
✅ show ip ospf database external → Check Type-5 LSAs.
✅ show running-config | section redistribute → Ensure correct redistribution.
✅ debug ip ospf events → Monitor redistribution behavior.
🔴 If external routes are missing:
- Redistribution misconfigured →
redistribute <protocol> subnets - ACLs or route-maps filtering OSPF routes
- NSSA blocking external routes
Step 6: Debug & Monitor Logs
✅ debug ip ospf hello → Analyze Hello packet issues.
✅ debug ip ospf packet → Monitor overall OSPF packet exchange.
✅ show logging → Check for error messages.
NETWORKENGINEERSTUFF
