The thing is:
You have a VPN Service, so:
A. Can be enabled inside the Router
1) Router mode PPTP, most routers support by factory firmware
2) Router mode OpenVPN(seems better), need to install open source firmware DD-WRT in the Router OR have a openvpn factory supported Router (expensive)
B. Can be enabled directly inside the raspberry, also with same 2 options:
1) PPTP, use pppd/pon connection like dreampi does, kind of pan in the ass to make work together, need to be started after dreampi, otherwise will be killed. Work without forwarding ports from dreamcast IP to VPN connection
2) OpenVPN for raspberry (tun0), I can make it to talk with dreamcast (ppp0), but like above, can't foward ports yet, ok for games without dmz need.
C. Can be enabled inside the android or windows, but this don't help dreamcast hardware.
I am trying to get a best method to open ports to all games
On my tests, the simple PPTP router solution [ A1 ] already open connection for some games, that will not work without the VPN , if you dont have a dmz functional ISP (CGNAT)
Basically, Sports games still not work, that's why i am trying raspberry OpenVPN method [B2], because NBA works using that on "android vs dreamcast dmz'ed"
Still want to custom my tplink router with DD-WRT firmware [A2] that support openvpn inside the router.
Also, I am aware about the small number of possible interested persons, but is a challenge anyway
Below you see My raspberry with OpenVPN Miami US (purevpn tcp server), dreampi get his IP range , i did some tricks to share the connection between them, but missing port forwarding. [B2]
Also a PPTP raspberry connection. [B1]
Look for : sudo pon purevpn

