For the last couple months, we've been losing internet connection at our small business about every night. The LAN seems fine. The main components are: AT&T Uverse ISP, a Sonicwall TZ 105, a Dell 24 port 100Mb switch with two Gb ports, and a Windows Server 2012.
Rebooting the AT&T modem fixes it, but it may take two or three reboots sometimes. Once it is rebooted, the connection will be fine all day until the next night sometime. It seems as though it started shortly after AT&T switched us from regular service to Uverse service, but that just may be coincidence. AT&T says their lines appear good.
I've tried replacing the AT&T modem (with the help of a technician who verified the modem settings, since we have a router behind the modem), different Ethernet cables, and the router (was a Linksys, now the Sonicwall). The only modifications to the router are a static IP, DHCP enabled, a VPN tunnel to a remote office, and several opens ports, such as RDP.
My next thoughts were to switch to NIC2 on the server or replace the switch.
Not sure where to look next or even what time the connection goes down to see if there is a conflict somewhere with a nightly service.
Thanks for your help.