I've been having some problems with my internet connection, whereby sometimes sites take an age to load yet some (such-as Google) are generally available all the time. The pages also work eventually, as opposed to the connection dropping and the page loads failing.
I've tried using various tools to analyse the problem, such as Firebug and Tamperdata, but they've not been able to tell me anything beyond that some requests have taken a while (up to 3 minutes timed) to resolve. I'm thus thinking that the problem is at a lower level than they can tell me about.
The problem is most noticeable when I open a bunch of tabs to different sites, some of the content loads but some pages (and some sections of other pages) remain in a loading state for ages. I thought at first it could be an intermittent issue with my ISP's DNS, as I'd generally have a cached copy of Google's IP but might not for other sites, but I switched to Google's public DNS and still experienced the same problems.
So, any ideas where the problem could be, or what tool might help me pin this down further? I've contacted my ISP and they've been generally helpful, they sent me a new (better) router in the hopes that it would solve the problem, but unfortunately I'm still occasionally getting this issue.