Chapter 10 Network Address Translation
NBG-418N v2 User’s Guide
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Figure 80 Trigger Port Forwarding Process: Example
1 Jane requests a file from the Real Audio server (port 7070).
2 Port 7070 is a “trigger” port and causes the NBG-418N v2 to record Jane’s computer IP address.
The NBG-418N v2 associates Jane's computer IP address with the "incoming" port range of 6970-
7170.
3 The Real Audio server responds using a port number ranging between 6970-7170.
4 The NBG-418N v2 forwards the traffic to Jane’s computer IP address.
5 Only Jane can connect to the Real Audio server until the connection is closed or times out. The
NBG-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 Two Points To Remember About Trigger Ports
1 Trigger events only happen on data that is coming from inside the NBG-418N v2 and going to the
outside.
2 If an application needs a continuous data stream, that port (range) will be tied up so that another
computer on the LAN can’t trigger it.
Jane’s computer
Real Audio Server
Port 7070
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