The Port Triggering Screen - ZyXEL Communications SBG5500-A User Manual

Table 43 Port Forwarding: Add/Edit (continued)
LABEL
WAN IP
Port Mapping
Type
Starting Port
Ending Port
To LAN Site
LAN IP Address
Translation Start
Port
Translation End
Port
OK
Cancel

8.3 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.
Trigger port forwarding solves this problem by allowing computers on the LAN to dynamically take turns
using the service. The SBG 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 SBG's WAN port
receives a response with a specific port number and protocol ("open" port), the SBG 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:
Chapter 8 Network Address Translation (NAT)
DESCRIPTION
Enter the WAN IP address for which the incoming service is destined. If the packet's destination
IP address doesn't match the one specified here, the port forwarding rule will not be applied.
Select Port if you only want to enter the starting port. Select Ports if you want to enter both
starting and ending ports (1-65535).
Enter the original destination port for the packets.
To forward only one port, enter the port number again in the End Port field.
To forward a series of ports, enter the start port number here and the end port number in the End
Port field.
Enter the last port of the original destination port range.
To forward only one port, enter the port number in the Start Port field above and then enter it
again in this field.
To forward a series of ports, enter the last port number in a series that begins with the port
number in the Start Port field above.
Enter the inside IP address of the virtual server here.
This shows the port number to which you want the SBG to translate the incoming port. For a
range of ports, enter the first number of the range to which you want the incoming ports
translated.
This shows the last port of the translated port range.
Click OK to save your changes.
Click Cancel to exit this screen without saving.
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