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.