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Triangle 54 — OSPF build
Enterprise Intermediate 6 devices 11 checked tasks 106 points Plan lab
Scenario — Ludhiana, Lucknow and Noida are cabled in a triangle, so every office has two ways to every other. Nothing is configured. The address plan: LANs Ludhiana 10.73.1.0/24, Lucknow 10.73.2.0/24, Noida 10.73.3.0/24; links Ludhiana–Lucknow 172.21.53.0/30, Lucknow–Noida 172.21.53.4/30, Noida–Ludhiana 172.21.53.8/30. Give every router interface its address (the router takes .1 of its LAN, the first address of a /30 goes to the lower-numbered router), then make OSPF carry the routes. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This lab is part of the full simulator: open it free for 7 days with a new account, then with a plan. It needs an account, which keeps your progress.
The scenario
Ludhiana, Lucknow and Noida are cabled in a triangle, so every office has two ways to every other. Nothing is configured. The address plan: LANs Ludhiana 10.73.1.0/24, Lucknow 10.73.2.0/24, Noida 10.73.3.0/24; links Ludhiana–Lucknow 172.21.53.0/30, Lucknow–Noida 172.21.53.4/30, Noida–Ludhiana 172.21.53.8/30. Give every router interface its address (the router takes .1 of its LAN, the first address of a /30 goes to the lower-numbered router), then make OSPF carry the routes.
Your role: a network engineer on the enterprise team. Level: Intermediate Done when: all 11 goals show as passed (106 points).
Network status
Devices: 3 routers, 3 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. PC-Ludhiana is a host with 10.73.1.10/24, gateway 10.73.1.1. PC-Lucknow is a host with 10.73.2.10/24, gateway 10.73.2.1. PC-Noida is a host with 10.73.3.10/24, gateway 10.73.3.1. R-Ludhiana, R-Lucknow, R-Noida start with an empty configuration. Known problems
None: nothing is misconfigured. The routers are simply not finished: the goals list what has to be built. Goals
Address R-Ludhiana: g0/0 10.73.1.1/24, g0/1 172.21.53.1/30, g0/2 172.21.53.10/30 (8 pts) Address R-Lucknow: g0/0 10.73.2.1/24, g0/1 172.21.53.2/30, g0/2 172.21.53.5/30 (8 pts) Address R-Noida: g0/0 10.73.3.1/24, g0/1 172.21.53.6/30, g0/2 172.21.53.9/30 (8 pts) R-Ludhiana has 2 OSPF neighbours in FULL (8 pts) R-Lucknow has 2 OSPF neighbours in FULL (8 pts) R-Noida has 2 OSPF neighbours in FULL (8 pts) OSPF process 70, area 0, with router-IDs 1.1.1.1 … 3.3.3.3 and passive LAN ports (12 pts) R-Ludhiana learns 10.73.3.0/24 from the protocol (10 pts) 10.73.1.10 (Ludhiana) reaches 10.73.3.10 (Noida) (12 pts) 10.73.2.10 (Lucknow) reaches 10.73.1.10 (Ludhiana) (12 pts) Every LAN reaches every other LAN (12 pts) The activity, in order
Address every interface from the plan: each router task lists its ports and addresses. Why: A router interface routes nothing until it has an address and is up. Every other task builds on this one. Verify with: show ip interface brief Enable OSPF on each router and advertise its LAN and links; keep LAN ports passive. Why: A router interface routes nothing until it has an address and is up. Every other task builds on this one. Verify with: show ip interface brief Read the routing table of every router and compare it with the plan. Why: A router interface routes nothing until it has an address and is up. Every other task builds on this one. Verify with: show ip interface brief Ping from each LAN to every other LAN, in both directions. Why: OSPF routes only flow over a FULL adjacency. If a neighbour is stuck in INIT or EXSTART, compare the two ends’ settings. Verify with: show ip ospf neighbor Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: A subnet mask instead of a wildcard mask in a network statement Common mistake: Different area numbers on the two ends of a link Common mistake: Leaving the LAN port active so hellos leak to hosts Why this matters
OSPF routers exchange link-state advertisements and each builds the same map of the area, so a new LAN is found everywhere without touching the other routers. Neighbours form only when area, subnet and timers agree.
What you will be able to do
Enable OSPF with a router-id and network statements
Read neighbour state and the learned routes
Find an area mismatch
The network
ISR 2911, PC — 6 devices in all, already cabled.
Fa0 Gi0/0 Fa0 Gi0/0 Fa0 Gi0/0 Gi0/1 Gi0/1 Gi0/2 Gi0/1 Gi0/2 Gi0/2 R-Ludhiana PC-Ludhiana 10.73.1.10/24 · gw 10.73.1.1 R-Lucknow PC-Lucknow 10.73.2.10/24 · gw 10.73.2.1 R-Noida PC-Noida 10.73.3.10/24 · gw 10.73.3.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R-Ludhiana ISR 2911 configure it PC-Ludhiana PC 10.73.1.10 / 255.255.255.0 gw 10.73.1.1 R-Lucknow ISR 2911 configure it PC-Lucknow PC 10.73.2.10 / 255.255.255.0 gw 10.73.2.1 R-Noida ISR 2911 configure it PC-Noida PC 10.73.3.10 / 255.255.255.0 gw 10.73.3.1
Cabling
PC-Ludhiana Fa0 ↔ R-Ludhiana Gi0/0 PC-Lucknow Fa0 ↔ R-Lucknow Gi0/0 PC-Noida Fa0 ↔ R-Noida Gi0/0 R-Ludhiana Gi0/1 ↔ R-Lucknow Gi0/1 R-Lucknow Gi0/2 ↔ R-Noida Gi0/1 R-Noida Gi0/2 ↔ R-Ludhiana Gi0/2
What is configured at the start
Nothing is configured to start with beyond the addresses above: you build the configuration from a clean start.
Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 Address R-Ludhiana: g0/0 10.73.1.1/24, g0/1 172.21.53.1/30, g0/2 172.21.53.10/30 8 On R-Ludhiana: show ip interface brief — Gi0/0 has 10.73.1.1 and is up/up. and On R-Ludhiana: show ip interface brief — Gi0/1 has 172.21.53.1 and is up/up. and On R-Ludhiana: show ip interface brief — Gi0/2 has 172.21.53.10 and is up/up. 2 Address R-Lucknow: g0/0 10.73.2.1/24, g0/1 172.21.53.2/30, g0/2 172.21.53.5/30 8 On R-Lucknow: show ip interface brief — Gi0/0 has 10.73.2.1 and is up/up. and On R-Lucknow: show ip interface brief — Gi0/1 has 172.21.53.2 and is up/up. and On R-Lucknow: show ip interface brief — Gi0/2 has 172.21.53.5 and is up/up. 3 Address R-Noida: g0/0 10.73.3.1/24, g0/1 172.21.53.6/30, g0/2 172.21.53.9/30 8 On R-Noida: show ip interface brief — Gi0/0 has 10.73.3.1 and is up/up. and On R-Noida: show ip interface brief — Gi0/1 has 172.21.53.6 and is up/up. and On R-Noida: show ip interface brief — Gi0/2 has 172.21.53.9 and is up/up. 4 R-Ludhiana has 2 OSPF neighbours in FULL 8 On R-Ludhiana: show ip ospf neighbor shows at least 2 neighbour(s) in FULL. 5 R-Lucknow has 2 OSPF neighbours in FULL 8 On R-Lucknow: show ip ospf neighbor shows at least 2 neighbour(s) in FULL. 6 R-Noida has 2 OSPF neighbours in FULL 8 On R-Noida: show ip ospf neighbor shows at least 2 neighbour(s) in FULL. 7 OSPF process 70, area 0, with router-IDs 1.1.1.1 … 3.3.3.3 and passive LAN ports 12 On R-Ludhiana: show running-config contains the line(s) matching router ospf 70[\s\S]*router-id 1\.1\.1\.1. and On R-Lucknow: show running-config contains the line(s) matching router ospf 70[\s\S]*router-id 2\.2\.2\.2. and On R-Noida: show running-config contains the line(s) matching router ospf 70[\s\S]*router-id 3\.3\.3\.3. 8 R-Ludhiana learns 10.73.3.0/24 from the protocol 10 On R-Ludhiana: show ip route lists 10.73.3.0/24. 9 10.73.1.10 (Ludhiana) reaches 10.73.3.10 (Noida) 12 On PC-Ludhiana: ping 10.73.3.10 must succeed. 10 10.73.2.10 (Lucknow) reaches 10.73.1.10 (Ludhiana) 12 On PC-Lucknow: ping 10.73.1.10 must succeed. 11 Every LAN reaches every other LAN 12 On PC-Ludhiana: ping 10.73.2.10 must succeed. and On PC-Ludhiana: ping 10.73.3.10 must succeed. and On PC-Lucknow: ping 10.73.1.10 must succeed. and On PC-Lucknow: ping 10.73.3.10 must succeed. and On PC-Noida: ping 10.73.1.10 must succeed. and On PC-Noida: ping 10.73.2.10 must succeed.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
A subnet mask instead of a wildcard mask in a network statement
Different area numbers on the two ends of a link
Leaving the LAN port active so hellos leak to hosts
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
R-Ludhiana interface g0/0
ip address 10.73.1.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 172.21.53.1 255.255.255.252
no shutdown
exit
interface g0/2
ip address 172.21.53.10 255.255.255.252
no shutdown
exit
router ospf 70
router-id 1.1.1.1
network 10.73.1.0 0.0.0.255 area 0
network 172.21.53.0 0.0.0.3 area 0
network 172.21.53.8 0.0.0.3 area 0
passive-interface GigabitEthernet0/0
exit R-Lucknow interface g0/0
ip address 10.73.2.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 172.21.53.2 255.255.255.252
no shutdown
exit
interface g0/2
ip address 172.21.53.5 255.255.255.252
no shutdown
exit
router ospf 70
router-id 2.2.2.2
network 10.73.2.0 0.0.0.255 area 0
network 172.21.53.0 0.0.0.3 area 0
network 172.21.53.4 0.0.0.3 area 0
passive-interface GigabitEthernet0/0
exit R-Noida interface g0/0
ip address 10.73.3.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 172.21.53.6 255.255.255.252
no shutdown
exit
interface g0/2
ip address 172.21.53.9 255.255.255.252
no shutdown
exit
router ospf 70
router-id 3.3.3.3
network 10.73.3.0 0.0.0.255 area 0
network 172.21.53.4 0.0.0.3 area 0
network 172.21.53.8 0.0.0.3 area 0
passive-interface GigabitEthernet0/0
exit Where this is examined
CCNA 3.0 OSPFv2; CCNP ENARSI OSPF.
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