Virtual Server-Port Forwarding
The Router implements NAT to let your entire local network appear as a single machine to the Internet. The typical situation is that you have local servers for different services and you want to make them publicly accessible. With NAT applied, it will translate the internal IP addresses of these servers to a single IP address that is unique on the Internet. NAT function not only eliminates the need for multiple public IP addresses but also provides a measure of security for your LAN.
When the router receives an incoming IP packet requesting for access to your local server, the router will recognize the service type according to the port number in this packet (e.g., port 80 indicates HTTP service and port 21 indicates FTP service). By specifying the port number, you tell the router which service should be forwarded to the local IP address you specify.
After you setting the virtual server you should modify the filter rule whichever port and service you set on virtual server. Because the firewall has protect the route by filter rule so that you should update the filter rule after you set up virtual server.
Virtual Server allows you to make servers on your LAN accessible to Internet users. Normally, Internet users would not be able to access a server on your LAN because:
Your server does not have a valid external IP Address.
Attempts to connect to devices on your LAN are blocked by the firewall in this device.
The Virtual Server feature solves these problems and allows Internet users to connect to your servers, as illustrated below: