Allow access to WorkBook ONLY if on network

[CRIMEDOG]

I have an xlsm workbook, that I want to limit access to, unless you are connected to a specific network. So either on location - or through VPN.
(That way the user is authenticated)
Maybe open up a splash page that will go away if the user is connected.

Thanks for any suggestion!

[gmr4evr1]

Is the workbook saved on a drive on the specific network? If so, no one would have access to it unless they are connected to the network.
Or am I misunderstanding?