ZyXEL Communications LTE Series User Manual page 123

Unlike port forwarding that only forwards a service to a single LAN IP address, trigger port forwarding
allows computers on the LAN to dynamically take turns using a service. Doing away the need to
configure a new IP address each time you want a different LAN computer to use a service.
The Zyxel Device 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 Zyxel Device's WAN port
receives a response with a specific port number and protocol ("open" port), the Zyxel Device forwards
the traffic to the LAN IP address of the computer that sent the request. After the computer's connection
for that service closes, another computer on the LAN can use the service in the same manner.
For example:
Figure 95 Trigger Port Forwarding Process: Example
Jane requests a file from the Real Audio server (port 7070).
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Port 7070 is a "trigger" port and causes the Zyxel Device to record Jane's computer IP address. The Zyxel
2
Device associates Jane's computer IP address with the "open" port range of 6970-7170.
The Real Audio server responds using a port number ranging between 6970-7170.
3
The Zyxel Device forwards the traffic to Jane's computer IP address.
4
Only Jane can connect to the Real Audio server until the connection is closed or times out. The Zyxel
5
Device times out in three minutes with UDP (User Datagram Protocol) or two hours with TCP/IP (Transfer
Control Protocol/Internet Protocol).
Click Network Setting > NAT > Port Triggering to open the following screen. Use this screen to view your
Zyxel Device's trigger port settings.
Note: TCP port 7547 is reserved for system use.
Note: The maximum number of trigger ports for a single rule or all rules is 999.
The maximum number of open ports for a single rule or all rules is 999.
Chapter 9 Network Address Translation (NAT)
LTE Series User's Guide
123