network tap

A network tap is a hardware device which provides a way to access the data flowing across a computer network. Computer networks, including the Internet, are collections of devices, such as computers, routers, and switches, that are connected to each other. The connections can utilize different technologies, such as Ethernet, 802.11, FDDI, and ATM. In many cases, it is desirable for a third party to monitor the network traffic between two points in the network, point A and point B. 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. To place a tap between points A and B, the network cable between point A and point B is replaced with a pair of cables, one going to the tap's A port, one going to the tap's B port. The tap passes through all traffic between A and B, so A and B still think they are connected to each other, but the tap also copies the traffic between A and B to its monitor port, enabling a third party to listen.
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