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Lessons · IT support · the order you check

Check from the wall outward: power, cable, link, address, name, service

When something cannot reach something, check the layers in the order they depend on each other: power, then the cable, then the link light, then the address, then the name, then the service. Each one only makes sense if the one before it passed.

Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.

What it is for

'I cannot get to the intranet' could be a dead machine, a cable a foot has kicked out, a switch port, no address, DNS, or the intranet server itself. Start at the server and you check five things that were never wrong. Start at the wall and the first failed check is the layer the fault is in, and usually the fix.

How to think about it

Power: is it on. Cable: is it in, at both ends, in the right port. Link: is the little light on the port lit. Address: does it have a real one, not 169.254.x.x. Gateway: does ping to the gateway answer. Name: does a name resolve. Service: does the actual thing open. Stop at the first failure; that is the layer. Do not skip ahead because you have a hunch.

Worked example

Power: on. Cable: in at the wall and the laptop
Two layers, ten seconds, and they are the two most often kicked out of place.
Link light: lit, blinking
The switch sees the laptop. The cable and the port are working.
Address: 10.4.2.31, mask 255.255.255.0, gateway 10.4.2.1
A real address. DHCP gave one, so the network reached this machine.
ping 10.4.2.1 → reply. ping intranet → 'could not find host'
The gateway answers, so the wire and the address are fine. The name does not resolve. The fault is at the name layer, and the next tool is nslookup.

Your turn

The cable is in and the machine is on. Write the next layer to check.

power → cable →  → address → name → service

The trap

Starting at the service because the user said 'the intranet is down'. The user names the thing they wanted, which is the last layer. The fault is almost always lower.

Practise the order you check on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.