Firefox, IE not able to resolve domain names

Today I spent some time trying to figure out what was wrong with my daughter’s Windows XP Pro PC whose Internet browsers (both IE7 and Firefox 2.0) had stopped resolving domain names. Direct access to IP numbers worked as long as the web server being accessed was not redirecting to a domain name, and the LAN domain names (provided by a WINS server) were resolving correctly. Further, NSLOOKUP was working normally, and I could telnet from a command prompt both to LAN and WAN targets.

Some web-searching later I came across a thread in Tek-Tips (“Browser cannot resolve domain names”) that seemed to describe a similar scenario. Disappointingly, despite of many suggestions that were offered and tried, the person with the problem had ended up reinstalling WinXP to solve the problem.

So what had changed? I couldn’t remember making any changes on that PC, though of course my daughter could’ve made some change (if she had she didn’t admit to it 😉 ). But in the end it was Mea Culpa. In the Tek-Tips thread someone mentioned that the possible culprit could be a problem with a deterministic network driver. Hmm. To get some network application working on that computer I had disabled Kaspersky Internet Security firewall last night. It turns out that disabling the firewall disables DNS resolution on the computer (NSLOOKUP works because it talks to the name server directly). Shutting down KIS entirely didn’t make a difference, but once I re-enabled the firewall, things returned back to normal. I suppose had I uninstalled KIS it would have no longer interfered with the name resolution like it did when it was simply turned off.

For some reason it was not possible to respond to the thread in Tek-Tips Forums, so I leave this follow-up to the problem here. Maybe this info will save someone from having to reinstall XP in order to restore network access on their PC.