On my network I have a DC and Three PC's with a firewall that has the modem in bridged mode for connection to the internet. Every now and then the connection to the internet is not available the conputers can see the local network and connect to the server but no internet access. When I check the firewall it still has access to the internet and I can ping google but not the local network. So I restart the firewall and everything comes good again until it repeats itself again.

Start by ensuring that your network devices are are the latest firmware.

I have updated the firmware and still have dropouts. At present we have connected the firewall directly to the switch bypassing the wall connection to the patch panel then to the switch and so far have had no dropouts. Will keep you posted. Thanks for your reply.