A long chain with many links
When a page will not load, the cause could be in your phone, your router, your provider, a name lookup, an encrypted handshake or the server itself. They all feel the same to the person waiting, but they are very different problems. The useful question is where along the path things first stop working.
Walking the path
- The local link. Is the phone actually connected to the radio or Wi-Fi network, with a usable signal?
- The local network. Has the device been given an address, and can it reach its router?
- The provider. Can traffic get past the router to the wider internet?
- Name resolution. Can names be turned into addresses?
- The secure connection. Does the encrypted handshake with the remote service complete?
- The service itself. Is the server up and able to respond?
What the symptoms usually point to
Connected to Wi-Fi, but nothing loadsRouter, provider, or name resolution
Some sites work and others do notName resolution, routing, or filtering
Everything works, but slowlyCongestion, packet loss or a weak link
Works on mobile data, not on Wi-FiRouter, address assignment or local DNS
Breaks right after switching networksStale connections or a sign-in page
Telling failures apart
The practical method is to test the layers in order, from the bottom up: reach the router, reach a known address on the internet, resolve a name, complete a secure handshake, and fetch a small resource. The first step that fails shows which layer to look at, and which ones can be ruled out.
Because each probe is small and cheap, this can be done automatically and repeatedly, which turns a vague complaint into a specific diagnosis.
Why it is harder than it sounds
- Partial failures. Things are often degraded, not completely broken.
- Intermittent problems. A fault that comes and goes is easy to miss and hard to reproduce.
- Sign-in pages. Public networks often intercept traffic until you accept terms, which looks like a failure to many apps.
- The test depends on the network. The tool diagnosing the problem relies on the same connection that is failing.
KEY TAKEAWAYS
- A failure can occur at the link, the local network, the provider, name resolution, the secure handshake or the server.
- Symptoms narrow down the likely layer.
- Testing layers in order, bottom up, localizes the fault.
- Partial, intermittent and sign-in-page failures are the hardest to classify.