Operation Manual

Chapter 16 Network Address Translation (NAT)
NBG6515 User’s Guide
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Figure 92 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 to record Jane’s computer IP address. The NBG
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 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
times out in three minutes with UDP (User Datagram Protocol), or two hours with TCP/IP (Transfer
Control Protocol/Internet Protocol).
16.5.2 Two Points To Remember About Trigger Ports
1 Trigger events only happen on data that is going coming from inside the NBG 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.
Router
Router