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Chapter 17 Network Address Translation (NAT)
ZyWALL 2 Plus User’s Guide
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The following table describes the labels in this screen.
17.7 Port Triggering
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 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:
Table 96 ADVANCED > NAT > Port Forwarding
LABEL DESCRIPTION
Default Server In addition to the servers for specified services, NAT supports a default server. A
default server receives packets from ports that are not specified in this screen. If you
do not assign a Default Server IP address, the ZyWALL discards all packets
received for ports that are not specified here or in the remote management setup.
Go To Page Choose a page from the drop-down list box to display the corresponding summary
page of the port forwarding servers.
# This is the number of an individual port forwarding server entry.
Active Select this check box to enable the port forwarding server entry. Clear this check
box to disallow forwarding of these ports to an inside server without having to delete
the entry.
Name Enter a name to identify this port-forwarding rule.
Incoming
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.
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.
Server IP
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.