Another thing to look at is whether the problem affects all of the users on the network or it's limited to a subset of users.
If you determine that only some users are affected, check to see whether all those users are located on a common network segment.
One of the handiest tools for troubleshooting DNS failures is the NSLOOKUP command, which you can access from a Windows Command Prompt window.
Simply type followed by the name of the host for which you want to test the name resolution.
The problem was that a virus had integrated itself into the TCP/IP stack and was intercepting all name resolution requests.
Even though this initially appeared to be a DNS problem, the virus was ultimately to blame.
About a week ago, someone called me because every time they would try to visit certain Web sites they were redirected to a malicious Web site instead.
I initially suspected a DNS poisoning attack, but ruled out such an attack because only one computer was affected.
So it's critical to troubleshoot DNS problems as fast as possible. Here are10 of my favorite DNS troubleshooting techniques.
When DNS problems occur, one of the first things you should do is verify that the DNS server still has network connectivity.