ZyXEL Communications Intelligent Broadband Sharing Gateway P-324 - Manual (Page 133)

11-18 NAT
11.3.3 Trigger Port Setup
The Prestige records the IP address of a LAN computer that requests a service that you have defined as a
“trigger port”. The response from the Internet can then be forwarded directly to the LAN computer. Trigger
ports are transient; they only exist while in use or are timed out. The following is a trigger port example
Figure 11-12 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 Prestige to record Jane’s computer IP address. The
Prestige 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 Prestige 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
Prestige times out in three minutes with UDP (User Datagram Protocol) or two hours with TCP/IP
(Transfer Control Protocol/Internet Protocol).
Two Points To Remember About Trigger Ports
1. Trigger events only happen on outgoing data (from the Prestige to the WAN).
2. Only one LAN computer can use a trigger port (range) at a time.