I have a small intranet- and file-server inside our company, which can only be reached from inside our own network. I'd like to be able to reach the intranet and files on the server from outside the network, however I don't really like the idea of completely opening security by forwarding the ports on our NAT-router, so I'd prefer to enable a VPN possibility for this.

So I have a router, which is the DHCP server and has NAT function, and I have an Ubuntu Server with the files and intranet on it. How do I configure these two so that I can make a VPN connection with my network in order to reach the server?

thanks in advance for any answer!