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Port triggering is a port-forwarding system that automates the forwarding process and turns the port on and off when needed. This is more secure that manual port forwarding, because the port will turn off when the connection is finished, unlike port forwarding in which the port is open until the user shuts it off. This can only be done on a specific type of router, but the router is common. Only one port can be used at a time in port triggering, so servers that handle many ports and connections would not be suitable for this triggering method.
When a computer uses a router, typically for an Internet connection, it connects one port to the router system and sends out a command. The command may be to look into an email server or to access a website. The router implements the command and then sends data back into the computer. Another port, known as a forwarded port, is opened back to the computer and it supplies the data.
In a computer without port triggering enabled, the port will remain open. While harmless on its own, an open port can act as an open door for hackers. This makes it easy for a hacker to inject code into the open port or to sneak information out of the computer. In this scenario, the administrator must close the port manually.
Port triggering functions in a similar way but has an on and off button. This on and off button is not engaged by the user but by the data stream. When the user issues a command, the port is opened because of the requested data. After the data streams into the computer and there is nothing more coming in, then the triggered port is shut off. With it shut off, it is harder for hackers to enter the computer.
A problem with port triggering is that the same port cannot be used in the network by two or more computers. This occurs when the administrator programs a specific port to be the triggered port. If two computers attempt to access this specific port at once, there will be a conflict and it will not work for either computer. Servers handle many connections, so port triggering will not be useful and will end up accidentally severing many connections.
Only one type of router can handle port triggering. This is known as a network address translation (NAT) enabled router. These routers allow the computer access to two Internet protocol (IP) addresses for internal and external traffic.