It says in the Admin control panel.
Special Application
Some applications require multiple connections, such as Internet gaming, video conferencing, Internet telephony and others. These applications cannot work when Network Address Translation (NAT) is enabled. If you need to run applications that require multiple connections, specify the port normally associated with an application in the "Trigger Port" field, select the protocol type as TCP or UDP, then enter the public ports associated with the trigger port to open them for inbound traffic.
Note: The range of the Trigger Ports is from 1 to 65535.
Questions:Virtual Server
You can configure the router as a virtual server so that remote users accessing services such as the Web or FTP at your local site via public IP addresses can be automatically redirected to local servers configured with private IP addresses. In other words, depending on the requested service (TCP/UDP port number), the router redirects the external service request to the appropriate server (located at another internal IP address). This tool can support both port ranges, multiple ports, and combinations of the two.
1. What's the difference between Virtual Server and Special Application in its functionality?
2. I run both a web server and a mail server on this computer. When I use Special Application to forward port 80 and 25, the web service works, but mail service doesn't. On the contrary, the Virtual Server, which requires local IP configured, works perfectly. Why?
3. From question no.2, how does the router recognizes that my computer runs a web server even though Special Application doesn't need local IP configured?
4. When we tell the router to forward port 80 to the web server, other computers in the network can still normally browse web pages. Doesn't the router tell all the incoming connection on port 80 to the server?