Chapter 6 Network Address Translation (NAT)
PMG5318-B20B User’s Guide
43
6.2 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 GPON 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 GPON Device's WAN port receives a response with a specific port number and protocol
("open" port), the GPON 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:
Server IP
Address
Enter the inside IP address of the LAN device to which the virtual server forwards traffic.
Apply/Save
Click this button to save your changes.
External Port
Start
Enter the original destination port for the packets.
To forward only one port, enter the port number again in the
External End Port
field.
To forward a series of ports, enter the start port number here and the end port number in
the
External End Port
field.
External Port
End
Enter the last port of the original destination port range.
To forward only one port, enter the port number in the
External 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
External Start Port
field above.
Protocol
Select the protocol supported by this virtual server. Choices are
TCP
,
UDP
, or
TCP/UDP
.
Internal Port
Start
Enter the port number here to which you want the GPON 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.
Internal Port End Enter the last port of the translated port range.
Apply/Save
Click this button to save your changes.
Table 24
Virtual Servers Add (continued)
LABEL
DESCRIPTION
