I've been having some intermittent dns problems with a web server, where certain isp's dns servers don't have my hostnames in cache and fail to look them up. At the same time, queries to opendns for those hostnames resolve correctly. It's intermittent, and it always works fine for me, so it's hard to identify the problem when someone reports connectivity problems to my site.

My website is on a server running linux with Plesk. My dns records are configured with plesk (so my server is its own dns master). Domain name is registered with godaddy.

I'm not real knowledgeable about dns, so I don't really know how to begin with troubleshooting. I've started learning to use dig, but while I can read the manpage to learn the syntax, I don't really know what questions to ask.

Since the problem is intermittent I haven't been able to really catalog many symptoms.

Symptoms I have observed:

• Certain people repeatedly reported intermittent problems connecting to my website. This was only from certain networks. (Ex: One guy could connect reliably from his office but not his home.)

• Sometimes I notice my browser taking a long time looking up the hostname for my site (Firefox shows a message in the status bar at the bottom). For me this is in the ten second range.

• ssh connections from anywhere to my server take a long time to connect but then seem to work fine once connected.

So hopefully the folks on serverfault can point me to a good beginner tutorial for understanding dns, and suggest troubleshooting questions to ask next time one of my users reports connectivity problems.