Port triggering
Encyclopedia
Port triggering is a configuration option on a NAT
-enabled router that allows a host machine to dynamically and automatically forward
a specific port back to itself. Port triggering opens an incoming port when your computer is using a specified outgoing port for specific traffic.
in which outbound traffic on predetermined ports ('triggering ports') causes inbound traffic to specific incoming ports to be dynamically forwarded to the initiating host, while the outbound ports are in use. This allows computers behind a NAT
-enabled router on a local network
to provide services that would normally require the computer to have a fixed address on the local network. Port triggering triggers can open an incoming port
when a client on the local network makes an outgoing connection on a predetermined port or range of ports.
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 a NAT, the NAT silently drops this connection because it does not know which computer behind the NAT to send the request to connect.
In the case of port triggering, the router is configured so that when an outbound connection is attempted on any port between 6660-7000, it should allow inbound connections to that particular computer. 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. Security is also gained in a sense that the inbound port is not left open when not actively in use.
Network address translation
In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
-enabled router that allows a host machine to dynamically and automatically forward
Port forwarding
Port forwarding or port mapping is a name given to the combined technique of# translating the address and/or port number of a packet to a new destination# possibly accepting such packet in a packet filter...
a specific port back to itself. Port triggering opens an incoming port when your computer is using a specified outgoing port for specific traffic.
Description
Port triggering is a way to automate port forwardingPort forwarding
Port forwarding or port mapping is a name given to the combined technique of# translating the address and/or port number of a packet to a new destination# possibly accepting such packet in a packet filter...
in which outbound traffic on predetermined ports ('triggering ports') causes inbound traffic to specific incoming ports to be dynamically forwarded to the initiating host, while the outbound ports are in use. This allows computers behind a NAT
Network address translation
In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
-enabled router on a local network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
to provide services that would normally require the computer to have a fixed address on the local network. Port triggering triggers can open an incoming port
TCP and UDP port
In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication...
when a client on the local network makes an outgoing connection on a predetermined port or range of ports.
Example
As an example of how port triggering operates, when connecting to IRC, it's 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 a NAT, the NAT silently drops this connection because it does not know which computer behind the NAT to send the request to connect.
In the case of port triggering, the router is configured so that when an outbound connection is attempted on any port between 6660-7000, it should allow inbound connections to that particular computer. 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. Security is also gained in a sense that the inbound port is not left open when not actively in use.