ZyXEL Communications NBG-419N v2 - Trigger Port Forwarding Example; Two Points to Remember about Trigger Ports

Chapter 16 Network Address Translation (NAT)
NBG-419N v2 User’s Guide
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16.5.1 Trigger Port Forwarding Example
The following is an example of trigger port forwarding.
Figure 102 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 Router to record Jane’s computer IP address. The
Router 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 Router 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
Router 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 Router and going to the
outside.
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