Lab 6: OSPF Single-Area Configuration
Replace static routes with a routing protocol: three routers in a triangle running OSPF area 0, learning each other's LANs automatically — and rerouting when a link dies. Difficulty: Intermediate · Time: ~35 min.
Lab objectives
- Enable OSPF on three routers with correct network statements
- Set router IDs
- Watch neighbour adjacencies form
- Verify O routes and test failover
Topology & addressing
R1–R2–R3 in a triangle via /30 links (10.0.12.0/30, 10.0.23.0/30, 10.0.13.0/30); each router also has a LAN (192.168.1.0/24, .2.0/24, .3.0/24 on Gi0/0).
Step-by-step configuration
Each router:router ospf 1router-id 1.1.1.1 (2.2.2.2 / 3.3.3.3) | Start OSPF, set stable IDs |
R1: network 192.168.1.0 0.0.0.255 area 0network 10.0.12.0 0.0.0.3 area 0network 10.0.13.0 0.0.0.3 area 0 | Advertise LAN + both links (wildcard masks!). Repeat the pattern on R2/R3. |
Verification
show ip ospf neighbor — two neighbours per router in FULL state. show ip route ospf — O routes to the other LANs. Now shut R1–R2's link (shutdown) and ping again: traffic reroutes via R3 within seconds. That's dynamic routing earning its keep.
Next lab: labs hub · test yourself: CCNA practice test.
Frequently asked questions
What do the wildcard masks in network statements do?
They select which interfaces join OSPF: 0.0.0.3 matches a /30 link, 0.0.0.255 a /24 — the inverse of the subnet mask.
What does FULL state mean?
The routers have fully exchanged link-state databases and are proper OSPF neighbours.
Why set a router-id manually?
For stability and readability — otherwise OSPF picks the highest loopback/interface IP, which can change and confuse troubleshooting.
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