Multi-Area OSPF: Area 0 with Four Attached Areas
Multi-Area OSPF Lab
Area 0 backbone with four attached areas
Scenario
This lab follows the supplied OSPF exercise: R2 is in the Area 0 backbone, with R1, R3, R4 and R5 connecting LANs in Areas 1, 2, 3 and 4.
Networks from the supplied lab
| Router | Network | Area |
|---|---|---|
| R1 | 192.168.70.0/24 | 1 |
| R1-R2 | 172.16.29.0/30 | 0 |
| R2-R3 | 172.16.29.4/30 | 0 |
| R2-R5 | 172.16.29.8/30 | 0 |
| R2-R4 | 172.16.29.12/30 | 0 |
| R3 LAN | 192.168.71.0/24 | 2 |
| R4 LAN | 192.168.73.0/24 | 3 |
| R5 LAN | 192.168.72.0/24 | 4 |
Before OSPF
Verify all routed interfaces are up/up and each router can ping its directly connected neighbour. Do not start OSPF while Layer 1/2/3 addressing is already broken.
R1# show ip interface brief
R2# show ip interface brief
Configure OSPF process 100
R1(config)# router ospf 100
R1(config-router)# network 192.168.70.0 0.0.0.255 area 1
R1(config-router)# network 172.16.29.0 0.0.0.3 area 0
R2(config)# router ospf 100
R2(config-router)# network 172.16.29.0 0.0.0.3 area 0
R2(config-router)# network 172.16.29.4 0.0.0.3 area 0
R2(config-router)# network 172.16.29.8 0.0.0.3 area 0
R2(config-router)# network 172.16.29.12 0.0.0.3 area 0
R3(config)# router ospf 100
R3(config-router)# network 172.16.29.4 0.0.0.3 area 0
R3(config-router)# network 192.168.71.0 0.0.0.255 area 2
R4(config)# router ospf 100
R4(config-router)# network 172.16.29.12 0.0.0.3 area 0
R4(config-router)# network 192.168.73.0 0.0.0.255 area 3
R5(config)# router ospf 100
R5(config-router)# network 172.16.29.8 0.0.0.3 area 0
R5(config-router)# network 192.168.72.0 0.0.0.255 area 4
Verify in the right order
R2# show ip ospf neighbor
R2# show ip ospf interface brief
R2# show ip route ospf
R1# show ip route
First prove adjacency, then prove routes. A routing-table problem cannot be solved by staring only at ping.
End-to-end test
From the Area 1 LAN, ping hosts in Areas 2, 3 and 4. Use traceroute and identify which router moves traffic into Area 0 and out toward the destination area.
Break it
On one backbone-facing interface, intentionally place the OSPF network in the wrong area. Check neighbour state and routing behaviour. Restore the correct Area 0 configuration and verify recovery.
Reference
Networks, wildcard masks, areas and process ID are grounded in Task 10 of the supplied CCNA All LABS PDF. Explanations, verification order and break/fix challenge are AddySec original content.