I have one Windows server that does double duty as a SQL server. And I have Verizon DSL. Plus one unmanaged switch.
IP addy of Server: 192.168.1.2
IP addy of Verizon modem: 192.168.1.1
Only DNS setting on wired PCs are 192.168.1.1 and everything works great. My slow internet works and my critical app connects to the SQL db somehow.
Fast forward to yesterday – I order Cable Internet(Cox) – tech installs the cable modem (192.168.1.1) and the internet works but my critical app does not. It can’t find the SQL db but I can browse to the shares via the server ip address.
This is the following sequence that I can make it work for a short time. Enter 192.168.1.2 as the primary DNS and open critical app. Enter 192.168.1.1 as the alternate DNS and the internet works. After a few minutes – the critical app stops responding.
Everything goes back to normal if I plug back the Verizon modem.
There’s probably some configuration on the verizon router that is resolving the server name. But you can just use the Windows server as the DNS server for the network. On the Windows server, configure DNS forwards for some reliable Internet DNS servers (like Google or OpenDNS).