ZyXEL Communications NBG4604 - Two Points to Remember about Trigger Ports

Chapter 11 Network Address Translation (NAT)
NBG4604 User’s Guide
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2 Port 7070 is a “trigger” port and causes the NBG4604 to record Jane’s computer IP
address. The NBG4604 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 NBG4604 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 NBG4604 times out in three minutes with UDP (User Datagram
Protocol), or two hours with TCP/IP (Transfer Control Protocol/Internet Protocol).
11.5.2 Two Points To Remember About Trigger Ports
1 Trigger events only happen on data that is going coming from inside the NBG4604
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.