Chapter 11 Network Address Translation (NAT)
EX5501-B0 / AX7501-B0 / PX7501-B0 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 addresses this problem. 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.
Note: TCP port 7547 is reserved for system use.
Note: The maximum number of trigger ports for a single rule or all rules is 999.
Note: The maximum number of open ports for a single rule or all rules is 999.
For example:
Translation Start
Port
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
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
Select
Enable
to enter the source IP address of WAN interface.
Originating
IP
Enter the source IP address of WAN interface.
Protocol
Select the protocol supported by this virtual server. Choices are
TCP
,
UDP
, or
TCP/UDP
.
Cancel
Click
Cancel
to exit this screen without saving any changes.
OK
Click
OK
to save your changes.
Table 59 Port Forwarding: Add/Edit (continued)
LABEL
DESCRIPTION
