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5.5 Port Triggering
Port triggering can be used for dynamic port forwarding configuration. By
setting port triggering rules, you can allow inbound traffic to arrive at a spe-
cific LAN host, using ports different than those used for the outbound traffic.
This is called port triggering since the outbound traffic triggers to which ports
inbound traffic is directed.
For example, consider a gaming server that is accessed using UDP protocol on
port 2222. The gaming server responds by connecting the user using UDP on
port 3333 when starting gaming sessions. In such a case you must use port trig-
gering, since this scenario conflicts with the following default firewall settings:
• The firewall blocks inbound traffic by default.
• The server replies to GlobeSurfer 3G's IP, and the connection is not sent
back to your host, since it is not part of a session.
In order to solve this you need to define a port triggering entry, which allows
inbound traffic on UDP port 3333, only after a LAN host generated traffic to
UDP port 2222. This will result in accepting the inbound traffic from the gam-
ing server, and sending it back to the LAN host which originated the outgoing
traffic to UDP port 2222. Select the Port triggering tab on the security screen,
the Port triggering screen will appear (see figure 5.9). This screen will list all of
the port triggering entries.
• Let's add an entry for the gaming example above:
1. Click the New entry link to add an entry (see figure 5.10).
Figure 5.10: Adding Port Triggering Rules
2. Click the New user-defined service link to add an entry (see figure 5.11).
Figure 5.9: Port Triggering
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