Random changes are not troubleshooting. A structured method narrows the fault and gives you a record you can hand to the next person.
Start with the symptom
Write one sentence:
"Users on the second floor cannot reach the intranet, but internet access works."
That sentence tells you:
- who is affected;
- what works;
- what does not;
- the boundary of the problem.
Work the layers
| Layer | Question | Tools |
|---|---|---|
| Link | Is the interface up? | cable, link lights, ip link |
| Network | Do I have an IP, gateway and route? | ip addr, ip route, ping |
| Transport | Can I reach the port? | nc, telnet, Test-NetConnection |
| Application | Does the service respond correctly? | curl, dig, logs |
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