Pi-Hole is working well in blocking websites and advertisements. However, some of our students are very smart, they downloaded VPN services to their computers to bypass the pi-holes. I have regex VPN in the blacklist but because of the VPN, they managed to access websites we blocked. What is the solution for this?
I don't think you understand me it's pointless. You have to have ports open otherwise how to you talk to the outside world. The usage of vpn can be somewhat hindered. Even If only 1 of ports 123,53,80, and 443 are open to the outside they still have a way to a vpn. I am not a network administrator or system administrator. I think If you had some sort of proxy intercepting all traffic you could accomplish what you want. I would look down that path
EDIT
TLDR: You need those ports open for your network to operate.