My internet goes on and off without any changes to domain. Tested incoming internet line and equipment. Could this be a DHCP issue. I run a single server with DNS and DHCP and AD on it. It doesn't seem to be a wireless access point issue since it happens at all points of the network.
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How are the other machines connected to the LAN? All wireless? Are you getting drops on the internal network? Do a ping -t between several nodes to see if you're getting packet loss.