We have a problem that affects our entire local network where the external DNS completely fails for a minute or so a few times a day. I'm not sure if it happens on all computers at the same time or just on one at a time, but basically for a minute or so, the victim is not able to access anything that requires a DNS lookup.
For instance, just a minute ago, I got "Firefox can't find the server at en.wikipedia.org". I pinged en.wikipedia.org and got "Ping request could not find the host at en.wikipedia.org. Please check the name and try again." After about 20 seconds, I refreshed the page and was greeted by wikipedia as usual. The ping request also worked fine after this break. This happens several times a day and no sites are accessible except for (i believe) sites you were already browsing.
Every computer is connected to a single domain on Windows Small Business Server 2003, which runs through a SonicWall TZ170 firewall before going to the T1 modem. Has anyone heard of any issues that could cause this problem?
Edit: I am able to ping specific IP addresses while it is down, so it does appear to be a DNS issue.