I have 5 users with Mac laptops who want an automatic backup to be performed whenever they get to one of the three sites of their business (3 VLAN's connected via VPN). The Mac users connect to the network via Wi-Fi (same Wi-Fi network, same SSID on the three sites). The network is PC only, and the Mac laptops do not need the services of this network (they only need Wi-Fi to be able to go on the internet).
What would be the best solution for a Time Machine backup to start as soon as they connect to the Wi-Fi at any of the 3 sites? A server? A NAS? The Macs must stay independent, and not mix with the rest of the network.
If it's a server, should it simply be configured with an IP address in the range the VPN server serves the portables themselves?
Does anyone has dealt with this kind of situation?