Detection
Check Area ID on Each Router
R1:
R1# show ip ospf interface gi0/0 | include Area
Internet Address 10.1.1.1/30, Area 0
R2:
R2# show ip ospf interface gi0/0 | include Area
Internet Address 10.1.1.2/30, Area 10 ← MISMATCH!
Area 0 ≠ Area 10 = No adjacency
Debug Output
R1# debug ip ospf adj
*OSPF-1 ADJ: Rcv pkt from 10.1.1.2, area 10 : src not on the same area
Fix
Change R2's area to match R1:
R2(config)# router ospf 1
R2(config-router)# no network 10.1.1.0 0.0.0.3 area 10
R2(config-router)# network 10.1.1.0 0.0.0.3 area 0
Verify:
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/ - 00:00:35 10.1.1.1 Gi0/0
✅ Fixed!
Summary
✅ Check area IDs with show ip ospf interface
✅ Areas must match on both sides
✅ Fix by changing network statement area
Next: Authentication Mismatch (Article 21)
Internal Links:
- ← OSPF Neighbors Not Forming (Article 18)
- → Authentication Mismatch (Article 21)
