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Windows stopped to resolve names (both short and long) via DNS. Only hosts file is taken into account.

W2k8 x64 Enterprise server stopped (after scheduled reboot) to resolve names (both short and long) via DNS.
Server is not in the domain, nslookup works (with both DNS servers set).
But Windows (i.e. ping) doesn't even try to ask DNS.
We modified hosts file, deleted it, recreated, flushed DNS cache, stopped DNS cache service, added/removed domain suffixes, disabled IP v 6, disabled NetBt overTPC/IP, removed NIC teaming, rebooted many times.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider PRIO changed to 1.
DNS cache contains records from hosts file only.
After nslookup (neither after successful nor unsuccessful) DNS cache is not updated.
When DNS client service is disabled, names are still not resolved.

Still the same:

nslookup <server name> works (for both short and long names)
ping <server name> fails (for both short and long names)
Application works only for names we added to hosts.
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Top Expert 2012
Commented:
Reset the TCP\IP stack.

http://support.microsoft.com/kb/299357

Author

Commented:
finally downtime was confirmed, and TCP/IP stack reset solved the issue!
Warning:
don't forget to save IP config and routing table before the action ;)