Found this while digging around to fix a issue someone was having on the DIR-615 forums, and thought it would be useful here. This is something I never considered, and gives new light to different set ups you can do to allow port forwarding of the same port to be done to different devices. (WoW, PS3, XBL, etc). Enjoy. If required, I can move this, it has just come up alot on this forum.
What is the difference between Virtual Server and Port Forwarding?
Virtual Server - is used to forward a specific external port to an internal port in a one port to one port relationship. This would allow WAN side connections to come to the LAN side of your network. Virtual Server settings are commonly used for Port Redirection, when you use a public port that is different from the private port. This use is common if you are accessing multiple cameras. For for ease of use, you keep the cameras all on port 80 to view the web interface, but because the router will only allow port 80 to be opened to one IP, you would use Virtual server to redirect other ports to the LAN side cameras on port 80.
Example: In Virtual Server you would set your first camera as public port 81, private port of 80 and set it private IP accordingly. Then make the second camera public port 82, private port 80 and set its private IP accordingly. Internally (from LAN) both camera can be accessed at their IP address and port 80. From the outside(from WAN) they are access from the WAN ip address and their respective Public port, camera one at 81 and camera two at 82. http://wan-ip-address:81 typed into your browser will show you the web page of camera one.
Port Forwarding - is used to allow data to come from the WAN (Internet) and pass through the firewall to the destination ip address(s). This is used when a device or application behind the firewall of your router needs access to a range of ports to function properly. (E.g. online games or gaming consoles, FTP servers and network cameras.)
However, no two devices or machines on the LAN side of the router can use the same port number at the same time.
Example: In the case of the camera above, for Virtual Server, you kept the HTTP port as 80 and used Virtual Server to make the public port 81. To cover the streaming ports, Audio, Video, and control (DCS-5300G) you will have to set each port range unique to each camera and put those ranges in Port Forwarding. You can keep 5001-5003 for camera one but need to make camera two unique, may be 5004-5006.
In the end you will have used the Virtual Server for redirection and the Port Forwarding rules to allow a range of ports through the router to a LAN side device.
NOTE: In the older DI-Series routers, the Port Forwarding was referred to as Firewall.
