ZyXEL Communications 5 Series User Manual
Chapter 22 Network Address Translation (NAT)
ZyWALL 5/35/70 Series User’s Guide
445
22.5 The Port Triggering 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.
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 ZyWALL 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 ZyWALL's WAN port receives a response with a specific
port number and protocol ("incoming" port), the ZyWALL 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.
dynamically take turns using the service. The ZyWALL 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 ZyWALL's WAN port receives a response with a specific
port number and protocol ("incoming" port), the ZyWALL 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 257 Trigger Port Forwarding Process: Example
1 Jane (A) requests a file from the Real Audio server (port 7070).
Name
Enter a name to identify this port-forwarding rule.
Incoming
Port(s)
Port(s)
Enter a port number here. To forward only one port, enter it again in the second
field. To specify a range of ports, enter the last port to be forwarded in the second
field.
field. To specify a range of ports, enter the last port to be forwarded in the second
field.
Port Translation
Enter the port number here to which you want the ZyWALL to translate the incoming
port. For a range of ports, you only need to enter the first number of the range to
which you want the incoming ports translated, the ZyWALL automatically calculates
the last port of the translated port range.
port. For a range of ports, you only need to enter the first number of the range to
which you want the incoming ports translated, the ZyWALL automatically calculates
the last port of the translated port range.
Server IP
Address
Address
Enter the inside IP address of the server here.
Apply
Click Apply to save your changes back to the ZyWALL.
Reset
Click Reset to begin configuring this screen afresh.
Table 133 ADVANCED > NAT > Port Forwarding
LABEL
DESCRIPTION