Port Triggers - THOMSON TWG850 User Manual

Chapter 2: Web Configuration

Port Triggers

Some Internet activities, such as interactive gaming, require that a PC on the WAN side of
your gateway be able to originate connections during the game with your game playing
PC on the LAN side. You could use the Advanced-Forwarding web page to construct a
forwarding rule during the game, and then remove it afterwards (to restore full
protection to your LAN PC) to facilitate this. Port triggering is an elegant mechanism that
does this work for you, each time you play the game.
Fig. 22
Port Triggering works as follows. Imagine you want to play a particular game with PCs
somewhere on the Internet. You make one time effort to set up a Port Trigger for that
game, by entering into Trigger Range the range of destination ports your game will be
sending to, and entering into Target Range the range of destination ports the other
player (on the WAN side) will be sending to (ports your PC's game receives on).
Application programs like games publish this information in user manuals. Later, each
time you play the game, the gateway automatically creates the forwarding rule necessary.
This rule is valid until 10 minutes after it sees game activity stop. After 10 minutes, the
rule becomes inactive until the next matched outgoing traffic arrives.
For example, suppose you specify Trigger Range from 6660 to 6670 and Target Range
from 113 to 113. An outbound packet arrives at the gateway with your game-playing PC
source IP address 192.168.0.10, destination port 666 over TCP/IP. This destination port
is within the Trigger destined for port 113 to your game-playing PC at 192.168.0.10.
You can specify up to 10 port ranges on which to trigger.
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