@ERickP 

 

If you already establish the VPN tunnel, you can directly access your server's IP address and port. Do not need to access 10.10.10.104. Suppose that your server IP address and port is 10.1.1.222 :8080. After you connect to VPN, just need to directly  access 10.1.1.222:8080. 

Tunnel is in NAT mode. I can change it to route mode if that helps, but does not explain the issue why I CAN access the mgmt console at the VPN IP but CANT access the vpn_ip:81

@ERickP 

 

You said that your router has a virtual server for port 81. Please note that this virtual server means port forwarding. It means that you can access WAN IP: 81 to access the server in your local network. It doesn't means that you can access WAN IP:81 to access the router's management interface.

 

And you CAN access the mgmt console at the VPN IP, becasue you were accessing the management interface of router. You can think that VPN IP is another IP address of the router. But if you access VPN IP:81, port 81 isn't a management port of router, so the router will not reply you. ( Virtual server is used to forward that traffic that access WAN IP:81 not VPN IP:81.) 

 

Anyway, if you want to access the router's management web, you can access VPN IP:80. If you want to access the server in your local network, you can access their local IP address and TCP/UDP port directly if already established VPN.