We have two DHCP servers (Domain controllers) on our active directory. ADC1 is a Windows 2003 machine, ADC2 is Windows 2008.
One of our servers (SQL) keeps dropping connections. For example: for 2 minutes it will ping properly, and shares show up when accessed via the network (\\sql). Afterwards, it drops the connection, and becomes un-pingable. After a brief period, it comes back online, and responds to ping requests.
Some workstations on the network don't have the problem. Some constantly switch between working and non-working. Reboot of ADC's and the SQL itself does not help.
Computers connected to either ADC1 or ADC2 have the same problem. (for example one PC on ADC1 dhcp lease will pick up SQL wihout drops in connection, while another, on the same dhcp server, has the connection dropped).
SQL is on static ip, it's Event Viewer does not show any changes in network, services or drivers failure. No automatic updates, no expired licenses, no limited number of simultaneous users, no new ip address leases. Workstations also don't change IP's, even though they're on DHCP.
Any ideas on what could be causing SQL to drop and re-establish connections?
The only suspicious log I found on ADC1 was "The dns server has enountered numerous run-time events. To determine the initial cause of these run-time events, examine the DNS server event log entries that precede this event...." Event id:3000.
Unfortunately, the log does not show anything prior to this event.