Network Problem Finder (guided)

A few questions that narrow a network problem to the layer it is actually on.

What is affected?

Where this comes from

Each question eliminates a whole class of cause rather than working down a list. The first — whether everything is affected, one device, one site, or nothing specific — is the most valuable, because those four have almost nothing in common and most advice on the internet answers the wrong one. From there the branches end in something specific, and where a measurement would settle it the path names the tool on this site that takes it: the DNS-or-connection check separates the two layers in seconds, and the bufferbloat and call-readiness tests measure the things a speed test cannot see.

What the results mean

Everything down: Points at the line or the router. Nothing on a single device will fix it, and the checks are cheap and fast.
One device: The network is fine and that device's connection to it is not. On Wi-Fi, forgetting and rejoining the network fixes most of these.
One site: Almost never your connection. Check whether it is down for everyone before changing anything at your end.
Working but unreliable: The interesting case, and the one a speed test cannot diagnose — bufferbloat, jitter and peak-time contention all look like "it is slow".

Common problems and fixes

It says my connection is fine and it is clearly not: Follow the "working but unreliable" branch. A connection can pass every basic check and still be unusable for calls, and that is a queueing or loss problem rather than a connectivity one.
I do not know if the router lights mean anything: Answer "I cannot tell" — the tree carries on to the layer check, which is a measurement rather than an interpretation.
This is a work network: The branches still apply and the fixes may not: managed networks add proxies, policies and split DNS that this does not model, and the answer is frequently to report it rather than to change something.

Frequently asked questions

How do I work out why my internet is not working?

Start by establishing the scope, because it eliminates most of the possibilities immediately. Everything down on every device points at the line or the router. One device points at that device. One site points at that site. And a connection that works but feels unreliable is a different problem entirely — usually queueing or packet loss, which no amount of restarting will change.

Should I restart the router?

It is worth doing once, for a full minute, when everything is down — a shorter cycle often does not reset the modem side. It is not worth doing for a single device, a single site, or a connection that works but stutters, and doing it repeatedly instead of measuring is how an afternoon disappears.

Why is my connection fast but unreliable?

Because speed and reliability are separate measurements that fail independently. A gigabit line that queues badly under load will ruin a video call while testing perfectly, and the tools that show it are the bufferbloat and call-readiness tests rather than a speed test.

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