I have been experiencing periodic disconnection issues on my network. My Win 2012 domain controller has DNS set to the OpenDNS service. I am running a Sonicwall NSA220 with filtering also enabled and pointing to Comcast DNS servers. I have 20 Mac users in an education program and they experience periodic problems with not being able to access their content. (Curiously, accessing the same content from a PC does not have these issues)
I have found that if I change the DNS on my DC to the Comcast DNS server, my disconnection problem goes away.
I don't think the issue is with OpenDNS service but I don't know quite else it could be.