Network tap

A network tap is a hardware device which provides a way to access the data flowing across a computer network. In many cases, it is desirable for a third party to monitor the traffic between two points in the network. If the network between points A and B consists of a physical cable, a "network tap" may be the best way to accomplish this monitoring. The network tap has (at least) three ports: an A port, a B port, and a monitor port. A tap inserted between A and B passes all traffic through unimpeded, but also copies that same data to its monitor port, enabling a third party to listen.