ZyXEL Communications NBG-419N - Manual (Page 147)

Chapter 15 Network Address Translation (NAT)
NBG-419N User’s Guide
147
15.5.1 Trigger Port Forwarding Example
The following is an example of trigger port forwarding.
Figure 96 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-419N to record Jane’s computer
IP address. The NBG-419N 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-419N 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-419N times out in three minutes with UDP (User Datagram
Protocol), or two hours with TCP/IP (Transfer Control Protocol/Internet Protocol).
15.5.2 Two Points To Remember About Trigger Ports
1 Trigger events only happen on data that is going coming from inside the NBG-
419N 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.