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Troubleshoot — OSPF neighbours that will not form
Enterprise Intermediate 2 devices 3 checked tasks 100 points Plan lab
Two routers, one link, OSPF configured on both, the right network statements and the right area — and the neighbour table is empty. Hello and dead timers must match for an adjacency to form, and one side has been changed. Find it with show ip ospf interface and put it right. 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
Two routers, one link, OSPF configured on both, the right network statements and the right area — and the neighbour table is empty. Hello and dead timers must match for an adjacency to form, and one side has been changed. Find it with show ip ospf interface and put it right.
Your role: a network engineer on the enterprise team. Level: Intermediate Done when: all 3 goals show as passed (100 points).
Network status
Devices: 2 routers, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R1 starts with addresses (G0/1 10.0.12.1/30, L0 1.1.1.1/32) and OSPF 1 already configured. R2 starts with addresses (G0/1 10.0.12.2/30, L0 2.2.2.2/32) and OSPF 1 already configured. Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
R1 and R2 are OSPF neighbours (50 pts) R1 learns R2’s loopback (30 pts) R2 learns R1’s loopback (20 pts) The activity, in order
R1 and R2 are OSPF neighbours 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 R1 learns R2’s loopback Why: If the prefix is not in the routing table, the router drops packets for it, whatever else is configured. Verify with: show ip route R2 learns R1’s loopback Why: If the prefix is not in the routing table, the router drops packets for it, whatever else is configured. Verify with: show ip route 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: Checking only the network statements Common mistake: Changing one timer but not the dead interval Common mistake: Debugging with debug ip ospf adj left on Why this matters
OSPF neighbours must agree on hello and dead intervals (and area, mask, authentication, MTU) before they become adjacent. An empty neighbour table with correct network statements points at exactly this.
What you will be able to do
Use show ip ospf interface to read the timers on both ends
List the parameters that must match for an adjacency
Restore matching timers and confirm the neighbour reaches FULL
The network
ISR 2911 — 2 devices in all, already cabled.
Gi0/1 10.0.12.1/30 Gi0/1 10.0.12.2/30 R1 R2 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R1 ISR 2911 configure it R2 ISR 2911 configure it
Cabling
R1 Gi0/1 ↔ R2 Gi0/1
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
R1 interface g0/1
ip address 10.0.12.1 255.255.255.252
no shutdown
exit
interface lo0
ip address 1.1.1.1 255.255.255.255
no shutdown
exit
router ospf 1
router-id 1.1.1.1
network 10.0.12.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0 R2 interface g0/1
ip address 10.0.12.2 255.255.255.252
no shutdown
exit
interface lo0
ip address 2.2.2.2 255.255.255.255
no shutdown
exit
router ospf 1
router-id 2.2.2.2
network 10.0.12.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
interface g0/1
ip ospf hello-interval 3
ip ospf dead-interval 12
exit 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 R1 and R2 are OSPF neighbours 50 On R1: show ip ospf neighbor shows at least 1 neighbour(s) in FULL. 2 R1 learns R2’s loopback 30 On R1: show ip route lists 2.2.2.2/32. 3 R2 learns R1’s loopback 20 On R2: show ip route lists 1.1.1.1/32.
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
Checking only the network statements
Changing one timer but not the dead interval
Debugging with debug ip ospf adj left on
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:
R2 interface g0/1
no ip ospf hello-interval
no ip ospf dead-interval
exit Where this is examined
CCNA (OSPF), CCNP ENCOR/ENARSI (OSPF troubleshooting), Network+ (routing issues).
This lab practises these topics in the zNetLaB certification courses:
Related labs
Where to start
The lessons all guided labs plans
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