User's Manual

Chapter 11 Network Address Translation (NAT)
NBG-417N User’s Guide
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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
The following table describes the labels in this screen.
Table 48 Network > NAT > Advanced
LABEL DESCRIPTION
# This is the rule index number (read-only).
Name Type a unique name (up to 15 characters) for identification purposes. All
characters are permitted - including spaces.
Incoming Incoming is a port (or a range of ports) that a server on the WAN uses when it
sends out a particular service. The NBG-417N forwards the traffic with this port
(or range of ports) to the client computer on the LAN that requested the service.
Start Port Type a port number or the starting port number in a range of port numbers.