Nat Advanced Screen - ZyXEL Communications NBG4604 User Manual

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 NBG4604 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 NBG4604's WAN port
receives a response with a specific port number and protocol ("incoming" port),
the NBG4604 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 NBG4604'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 73 Network > NAT > Advanced
128
NBG4604 User's Guide