ZyWALL 2 Series User’s Guide
LAN computer, you have to manually replace the LAN computer's IP address in the forwarding port with another LAN computer's IP address,
Trigger port forwarding solves this problem by allowing computers on the LAN to dynamically take turns using the service. The ZyWALL records the IP address of a LAN computer that sends traffic to the WAN to request a service with a specific port number and protocol (a "trigger" port). When the ZyWALL's WAN port receives a response with a specific port number and protocol ("incoming" port), the ZyWALL forwards the traffic to the LAN IP address of the computer that sent the request. After that computer’s connection for that service closes, another computer on the LAN can use the service in the same manner. This way you do not need to configure a new IP address each time you want a different LAN computer to use the application.
28.5.1 Trigger Port Forwarding Process
The following is an example of trigger port forwarding.
Figure1.A requests a file from the Real Audio server (port 7070).
2.Port 7070 is a “trigger” port and causes the ZyWALL to record A’s computer IP address. The ZyWALL associates A's computer IP address with the "incoming" port range of
3.The Real Audio server responds using a port number ranging between
4.The ZyWALL forwards the traffic to A’s computer IP address.
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