Two Points To Remember About Trigger Ports - ZyXEL Communications NBG-418N v2 User Manual

Jane requests a file from the Real Audio server (port 7070).
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Port 7070 is a "trigger" port and causes the NBG-418N v2 to record Jane's computer IP address. The
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NBG-418N v2 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 NBG-418N v2 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 times out. The NBG-
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418N v2 times out in three minutes with UDP (User Datagram Protocol), or two hours with TCP/IP (Transfer
Control Protocol/Internet Protocol).
10.6.5 T wo Po ints T o Re m e m b e r Ab o ut T rig g e r Po rts
Trigger events only happen on data that is coming from inside the NBG-418N v2 and going to the
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outside.
If an application needs a continuous data stream, that port (range) will be tied up so that another
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computer on the LAN can't trigger it.
Chapter 10 Network Address Translation
NBG-418N v2 User's Guide
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