ZyXEL Communications VMG8924-B10D User Manual page 166

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 VMG 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 VMG's WAN port
receives a response with a specific port number and protocol ("open" port), the VMG 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.
For example:
Figure 78 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 VMG to record Jane's computer IP address. The VMG
2
associates Jane's computer IP address with the "open" port range of 6970-7170.
The Real Audio server responds using a port number ranging between 6970-7170.
3
The VMG 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 VMG
5
times out in three minutes with UDP (User Datagram Protocol) or two hours with TCP/IP (Transfer Control
Protocol/Internet Protocol).
Click Network Setting > NAT > Port Triggering to open the following screen. Use this screen to view your
VMG's trigger port settings.
Chapter 11 Network Address Translation (NAT)
DSL
VMG8924-B10D/B30D User's Guide
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