I DON'T mean there is a VPN serving making from linux. The fact is that: I set up a VPN server using windows server(IP:192.168.1.1) and it is behind a Linux server which is using iptables for nat iptables -A PREROUTING -d 218.0.0.0 -j DNAT --to 192.168.1.1 but I can't establish the VPN connection from out(etc IP address is 218.10.0.1, I have tested that I can connect to other service such as web(port 80). How can I establish the VPN connection ? Is there need some setting in IPTABLES?