Chapter 11 Network Address Translation (NAT)
Nebula Mobile Router User’s Guide
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11.3 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 allows computers on the LAN to dynamically take turns using the service.
The Zyxel Device 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 Zyxel Device's WAN port
receives a response with a specific port number and protocol (\"open\" port), the Zyxel Device 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:
Start Port Configure this for a user-defined entry. 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.
End Port Configure this for a user-defined entry. 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.
Translation Start
Port
Configure this for a user-defined entry. This shows the port number to which you want the Zyxel
Device 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.
Translation End
Port
Configure this for a user-defined entry. This shows the last port of the translated port range.
Server IP Address Enter the inside IP address of the virtual server here.
Configure
Originating IP
Click the Enable check box to enter the originating IP in the next field.
Originating IP Enter the originating IP address here.
Protocol Select the protocol supported by this virtual server. Choices are TCP, UDP, or TCP/UDP.
OK Click this to save your changes.
Cancel Click this to exit this screen without saving.
Table 72 Network Setting > NAT > Port Forwarding: Add or Edit (continued)
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