What Is Port Triggering Used For on a Router?by Aaron Parson
Regular Web browsing uses a two-way transmission between your computer and the Internet. Other online programs, however, including online games and file sharing software, need to receive signals that originate from the Internet. The port triggering feature on routers tells the router to send these signals to a particular computer on your network, based on a trigger that activates when your computer sends a signal on a monitored port.
How Routers Route
In order to properly direct Internet messages to the computers on your local network, routers use Network Address Translation. This technology keeps track of outgoing signals in order to forward their corresponding responses to the correct computer. When signals to your network originate from the Internet, however, your router cannot tell which computer to forward to. Working around this problem requires manual setup using port forwarding or triggering.
Port Forwarding vs. Port Triggering
Port forwarding works around NAT issues by instructing the router to always direct messages on particular ports -- essentially channels of data -- to particular computers. Port triggering works similarly, but more conservatively. Instead of opening a port indefinitely, the router only links a port to a particular computer for a short period of time. This link is triggered when the router detects an outgoing signal on a specified port.
Advantages Over Port Forwarding
Port forwarding leaves forwarded ports open continually, causing a weak point in your network's security -- in addition to routing signals, NAT also acts as a firewall by keeping ports closed. By using triggering, you limit how long your ports remain exposed. Port triggering also works well for situations where different computers may need access to the same port at different times. For example, many online games require specific open ports. If you play a game on two different computers, you can set up both with port triggering, allowing the router to determine which machine needs the port at any given time.
Setting Up Port Triggering
To enable triggering, log in to your router's Web setup page. The exact setup method varies by router brand, model and firmware version, but you can generally find port triggering options near the port forwarding settings. On Netgear routers, for example, both appear on the "Port Forwarding/Port Triggering page," while Linksys routers have triggering options on the "Port Range Triggering" page under the "Applications and Gaming" tab. Setup works similarly to port forwarding, requiring the incoming port number provided by your software, but also requires an outgoing port number or range the router watches to set off the trigger. In most cases, you can use the same port numbers in this field.
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