What is Network tap, port mirroring?

A network tap is a device inserted in a link that copies its traffic to monitoring ports; a passive optical tap does it by splitting the light of each fibre, sending a fixed share (its split ratio) to the monitor, needs no power and adds only the length of its fibre. Port mirroring is a switch’s copying of the traffic of some of its ports to another port, in software or in its forwarding hardware.