I host a fairly basic database driven (MySQL+PHP) website for a client. It's only really used by them, and generally only from their office (single static IP).
They have over the past months complained that it gets painfully slow (>10s between clicking a link and the page updating). Whenever I have tested the site is lightning fast, and that includes testing the exact steps they're taking, at the same time as they do it (while on the phone to them). They've tried multiple browsers (IE and Chrome) and so have I. The problem only seems to exist from their site, and as they're the only people using it that's a big problem.
When they try to use the Internet for anything else, it's fast (or so I'm told, anyway).
Any suggestions as to what might cause a localised problem like this, and how to diagnose it? They have almost zero IT skills which doesn't help at all, but I have tried running a traceroute from my server to their external IP and it hasn't shown any obvious problems. I tried a ping test to look for dropped packets but their external IP isn't responding to ping and there's no way they could change that.
The server runs multiple sites, isn't heavily loaded, no other sites are reporting issues. I'm as sure as I can be that the problem is network not server related.
Mark