https://unix.stackexchange.com/questions/57656/how-to-access-a-machine-behind-a-restricted-nat-gateway-i-dont-manage

https://security.stackexchange.com/questions/155159/how-to-directly-connect-to-devices-behind-nat-from-the-internet

https://superuser.com/questions/37738/how-to-reliably-keep-an-ssh-tunnel-open

https://superuser.com/questions/470945/using-vnc-to-control-pc-behind-nat