SoftEther VPN User Forum

I installed SoftEther VPN Server on the Server that is behind NAT(ISP Router that connects directly to ISP Link through PPPoE) and Sophos SG230 Firewall.
Configurations on NAT(ISP Router/Modem): Portforwading Port 5555 to My Firewall External Port. (External Port connects Firewall to ISP router )
Configuration on Firewall: Open Port 5555, Portforwading Port 5555 to My SoftEther VPN Server
Configuration on SoftEther VPN Server: Port 5555 on listing state, created user and downloaded ssl certificate.

I am able to connect to VPN server from VPN Client when connected on the LAN. When connected from Public Network(Internet), i get the error message below
Error (Error Code 1):
Connection to the server failed. Check network connection and make sure that address and port number of destination server are correct.

You have a double NAT because of the modem/router AND Firewall. Try looking if there is a "bridge" mode on your modem/router combo, most of them has a way to make it just a dumb bridge so that your better firewall can do the job alone and not in double.