ZyXEL ZyWALL 5 User Guide - Page 445
The Port Triggering Screen
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Chapter 22 Network Address Translation (NAT) Table 133 ADVANCED > NAT > Port Forwarding LABEL DESCRIPTION Name Enter a name to identify this port-forwarding rule. Incoming Port(s) Enter a port number here. To forward only one port, enter it again in the second field. To specify a range of ports, enter the last port to be forwarded in the second field. Port Translation Enter the port number here to which you want the ZyWALL to translate the incoming port. For a range of ports, you only need to enter the first number of the range to which you want the incoming ports translated, the ZyWALL automatically calculates the last port of the translated port range. Server IP Address Enter the inside IP address of the server here. Apply Click Apply to save your changes back to the ZyWALL. Reset Click Reset to begin configuring this screen afresh. 22.5 The Port Triggering Screen Some services use a dedicated range of ports on the client side and a dedicated range of ports on the server side. With regular port forwarding you set a forwarding port in NAT to forward a service (coming in from the server on the WAN) to the IP address of a computer on the client side (LAN). The problem is that port forwarding only forwards a service to a single LAN IP address. In order to use the same service on a different 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. For example: Figure 257 Trigger Port Forwarding Process: Example 1 Jane (A) requests a file from the Real Audio server (port 7070). ZyWALL 5/35/70 Series User's Guide 445