Trigger Port Forwarding Example; Two Points To Remember About Trigger Ports - ZyXEL Communications NBG6503 User Manual

Chapter 14 Network Address Translation (NAT)

14.5.1 Trigger Port Forwarding Example

The following is an example of trigger port forwarding.
Figure 86 Trigger Port Forwarding Process: Example
Jane requests a file from the Real Audio server (port 7070).
1
Port 7070 is a "trigger" port and causes the Router to record Jane's computer IP address. The
2
Router 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.
3
The Router forwards the traffic to Jane's computer IP address.
4
Only Jane can connect to the Real Audio server until the connection is closed or times out. The
5
Router times out in three minutes with UDP (User Datagram Protocol), or two hours with TCP/IP
(Transfer Control Protocol/Internet Protocol).

14.5.2 Two Points To Remember About Trigger Ports

Trigger events only happen on data that is going coming from inside the Router and going to the
1
outside.
If an application needs a continuous data stream, that port (range) will be tied up so that another
2
computer on the LAN can't trigger it.
122
Router
Router
NBG6503 User's Guide