AI Network Labs 06 — Lab: Single- and Multi-Area OSPF

Take the three-router topology from Lab 05, delete every static route, and let OSPF discover the network. Then add a second area — the same structure the capstone campus uses at scale.

1 · Single-area OSPF

Each router advertises its connected networks into area 0. Wildcard masks are the inverse of the subnet mask (/24 → 0.0.0.255, /30 → 0.0.0.3).

! R1
router ospf 1
 router-id 1.1.1.1
 network 192.168.1.0 0.0.0.255 area 0
 network 10.1.12.0 0.0.0.3 area 0
 passive-interface GigabitEthernet0/0

! R2
router ospf 1
 router-id 2.2.2.2
 network 10.1.12.0 0.0.0.3 area 0
 network 10.1.23.0 0.0.0.3 area 0

! R3
router ospf 1
 router-id 3.3.3.3
 network 10.1.23.0 0.0.0.3 area 0
 network 192.168.3.0 0.0.0.255 area 0
 passive-interface GigabitEthernet0/1

2 · Prompt

On the R1–R2–R3 topology, remove all static routes.
Configure OSPF process 1 with router IDs 1.1.1.1, 2.2.2.2, 3.3.3.3, everything in area 0,
LAN interfaces passive. Show commands first.
Then verify neighbours on R2 and ping LAN-A → LAN-C.

3 · Verify

show ip ospf neighbor
show ip route ospf
show ip protocols

R2 must show two FULL neighbours. R1's routing table should list 192.168.3.0/24 with code O.

4 · Going multi-area

Move R3's LAN into area 30 — R3 becomes an Area Border Router:

! R3
router ospf 1
 no network 192.168.3.0 0.0.0.255 area 0
 network 192.168.3.0 0.0.0.255 area 30

Now R1 learns the LAN as O IA (inter-area). That's exactly how the Cybernet Campus design keeps Building A (area 10), Building B (area 20) and the branches (area 30) apart while the core stays in area 0.

Exercise

Give R1 and R2 the same router ID. What does show ip ospf neighbor show, and what does Packet Tracer log? Fix it with clear ip ospf process.