A network tap instead is a fully passive device. Electrically or optically (e.g. using a prism) packets are copied onto the tap ports. Unless you use an aggregation tap, a tap has one tap port per direction. This means that in order to monitor 1 link, you need 2 NICs, one for the first and the other for the second direction. In this case you won’t ever loose a single packet as in the mirror case, because each direction is using a link, instead of merging both directions onto the same link. Network Taps are available for copper and Fiber lines from 1G to 100G. Fiber tap installation incurs minimal network latency. Copper based are technologies implemented to not disturb the network line in case of powerless Copper Tap.

Port mirroring is an approach to monitoring network traffic that involves forwarding a copy of each packet from one network switch port to another. Span Port (Port Mirroring) is not passive technology. Passive
means “have no effect and impact”. Using of Span is easy and fast deployed, but has some huge impacts.