Trigger Port Forwarding Example; Two Points To Remember About Trigger Ports - ZyXEL Communications NBG417N User Manual

Chapter 11 NAT

11.5.4 Trigger Port Forwarding Example

The following is an example of trigger port forwarding.
Figure 71 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 NBG4115 to record Jane's computer IP
2
address. The NBG4115 associates Jane's computer IP address with the "incoming"
port range of 6970-7170.
The Real Audio server responds using a port number ranging between 6970-7170.
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The NBG4115 forwards the traffic to Jane's computer IP address.
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Only Jane can connect to the Real Audio server until the connection is closed or
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times out. The NBG4115 times out in three minutes with UDP (User Datagram
Protocol), or two hours with TCP/IP (Transfer Control Protocol/Internet Protocol).

11.5.5 Two Points To Remember About Trigger Ports

Trigger events only happen on data that is going coming from inside the NBG4115
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and going to the outside.
If an application needs a continuous data stream, that port (range) will be tied up
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so that another computer on the LAN can't trigger it.
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User's Guide