ZyXEL Communications NXC5200 User Manual page 210

Chapter 12 Policy and Static Routes
computer. The problem is that port forwarding only forwards a service to a single
IP address. In order to use the same service on a different computer, you have to
manually replace the client computer's IP address with another client computer's
IP address.
Port triggering allows the client computer to take turns using a service
dynamically. Whenever a client computer's packets match the routing policy, it can
use the pre-defined port triggering setting to connect to the remote server without
manually configuring a port forwarding rule for each client computer.
Port triggering is used especially when the remote server responses using a
different port from the port the client computer used to request a service. The
NXC records the IP address of a client computer that sends traffic to a remote
server to request a service (incoming service). When the NXC receives a new
connection (trigger service) from the remote server, the NXC forwards the traffic
to the IP address of the client computer that sent the request.
In the following example, you configure two services for port triggering:
Incoming service: Game (UDP: 1234)
Trigger service: Game-1 (UDP: 5670-5678)
Computer A wants to play a multiplayer online game and tries to connect to game
1
server 1 using port 1234. The NXC records the IP address of computer A when the
packets match a policy with SNAT configured.
Game server 1 responds using a port number ranging between 5670 - 5678. The
2
NXC allows and forwards the traffic to computer A.
Computer A and game server 1 are connected to each other until the connection
3
is closed or times out. Any other computers (such as B or C) cannot connect to
remote server 1 using the same port triggering rule as computer A unless they
are using a different next hop (gateway or outgoing interface) from computer A or
until the connection is closed or times out.
Figure 85 Trigger Port Forwarding Example
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NXC5200 User's Guide