User`s guide

Chapter 33 Network Address Translation (NAT)
LAN-Cell 2 User’s Guide
494
33.5 Trigger Port Forwarding
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 LAN-Cell 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 LAN-Cell's WAN port receives a response with a
specific port number and protocol ("incoming" port), the LAN-Cell 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.
33.5.1 Two Points To Remember About Trigger Ports
1 Trigger events only happen on data that is going coming from inside the LAN-Cell and
going to the outside.
2 If an application needs a continuous data stream, that port (range) will be tied up so that
another computer on the LAN can’t trigger it.
" Only one LAN computer can use a trigger port (range) at a time.
Enter 3 in menu 15 to display Menu 15.3 - Trigger Ports. For a LAN-Cell with multiple
WAN interfaces, enter 1 or 2 from menu 15.3 to go to Menu 15.3.1 or Menu 15.3.2 - Trigger
Port Setup and configure trigger port rules for the first or second WAN interface.