Editing Port triggering (section)

=== Example ===

As an example of how port triggering operates, when connecting to [[IRC]] (Internet Relay Chat), it is common to authenticate a username with the [[Ident protocol]] via port 113.

When connecting to IRC, the client computer typically makes an outgoing connection on port 6667 (or any port in the range 6660–7000), causing the IRC server to attempt to verify the username given by making a new connection back to the client computer on port 113. When the computer is behind NAT, the NAT device silently drops this connection because it does not know to which computer behind the NAT it should send the request to connect. These two transport-level connections are necessary for the application-level connection to the IRC server to succeed (see [[Internet protocol suite]]). Since the second [[TCP/IP]] connection is not possible, the attempted connection to the IRC server will fail.

In the case of port triggering, the router is configured so that when an outbound connection is established on any port from 6660 to 7000, it should allow inbound connections to that particular computer on port 113. This gives it more flexibility than static port forwarding because it is not necessary to set it up for a specific address on your network, allowing multiple clients to connect to IRC servers through the NAT-router. Security is also gained, in the sense that the inbound port is not left open when not actively in use.