ZyXEL Communications Parental Control Gateway HS100/HS100W - Manual (Page 140)

HomeSafe User’s Guide
9-10 NAT Screens
service (coming in from the server on the WAN) to the IP address of a computer on the client side
(LAN). The problem is that port forwarding only forwards a service to a single LAN IP address.
In order to use the same service on a different LAN computer, you have to manually replace the
LAN computer's IP address in the forwarding port with another LAN computer's IP address,
Trigger port forwarding solves this problem by allowing computers on the LAN to dynamically
take turns using the service. The HomeSafe records the IP address of a LAN computer that sends
traffic to the WAN to request a service with a specific port number and protocol (a "trigger" port).
When the HomeSafe's WAN port receives a response with a specific port number and protocol
("incoming" port), the HomeSafe forwards the traffic to the LAN IP address of the computer that
sent the request. After that computer’s connection for that service closes, another computer on the
LAN can use the service in the same manner. This way you do not need to configure a new IP
address each time you want a different LAN computer to use the application.
9.6.1 Trigger Port Forwarding Example
The following is an example of trigger port forwarding.
Figure 9-7 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 HomeSafe to record Jane’s computer IP address.
The HomeSafe 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 HomeSafe 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
HomeSafe times out in three minutes with UDP (User Datagram Protocol), or two hours with
TCP/IP (Transfer Control Protocol/Internet Protocol).
9.6.2 Two Points To Remember About Trigger Ports
1. Trigger events only happen on data that is going coming from inside the HomeSafe 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.
9.7 Configuring Trigger Port Forwarding
To change your HomeSafe’s trigger port settings, click SUA/NAT and the Trigger Port tab. The
screen appears as shown.