RESOLVED I have a corp network here with 50+ PC's, each using an internal DNS server. For some reason one computer on our network can no longer communicate with that DNS server. (It can occasionally). I can't ping it, and it wont resolve DNS queries. That computer can ping all other hosts on the network. All other hosts can ping the server fine. There is nothing specific about how this computer connects to the server. I have tried replacing its network cable, replacing its switch, by-passing the switch, rebooting, etc. An arp shows the computer has the correct MAC for the server. Any ideas?