Port Triggering is a dynamic form of Port Forwarding. Ports are opened when they are needed and closed when not in use. Because of this, triggered ports are more secure than traditional, static (manually configured) forwarded ports.
With port triggering, an application on a LAN host initiates traffic towards the Internet. The Triggering function remembers the traffic pattern. When that same pattern is identified as incoming from the WAN, the appropriate inbound port-mapping occurs. Traffic is then allowed through and forwarded to the correct host, and port. After a few minutes of inactivity, triggered ports are closed.
The image below represents the default Triggered Port Forwarding page. If this rule were enabled, FreshTomato would listen to any traffic from the LAN towards the Internet. If it found packets within the 3000-4000 port range which satisfied the matching criteria, it would automatically enable port forwarding inbound in the 5000-6000 port range towards the LAN IP address that originated the request.
On: This enables and disables the Triggered Port Forwarding function.
Protocol: Here, you can select which protocols are triggered through the ports being forwarded.
Trigger Ports: Here, enter the outbound ports to be monitored.
Forwarded Ports: Here, enter the port/s to be mapped when triggered.
Description: This fields allows you to enter notes notes as a reminder or reference.