ZyXEL Communications NBG-417N manual NAT Advanced Screen, 126

Chapter 11 Network Address Translation (NAT)

11.5 NAT Advanced Screen

Some services use a dedicated range of ports on the client side and a dedicated range of ports on the server side. With regular port forwarding you set a forwarding port in NAT to forward a 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 NBG-417N 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 NBG-417N's WAN port receives a response with a specific port number and protocol ("incoming" port), the NBG-417N 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.

To change your NBG-417N’s trigger port settings, click Network > NAT > Advanced. The screen appears as shown.

Note: Only one LAN computer can use a trigger port (range) at a time.

Figure 72 Network > NAT > Advanced

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NBG-417N User’s Guide