Definition - What does Port Mirroring mean?
Port mirroring is a method of copying and sending network packets transmitted as input from a port to another port of a monitoring computer/switch/device. It is a network monitoring technique implemented on network switches and similar devices.
Port mirroring is also known as switched port analyzer (SPAN) and roving analysis port (RAP).
Techopedia explains Port Mirroring
Port mirroring is implemented in local area networks (LAN), wireless local area networks (WLAN) or virtual local area networks (VLAN) to identify, monitor and troubleshoot network abnormalities. It is configured at the network switch by a network administrator (NA) or network monitoring/security application. When enabled, the traffic that emerges to and from a specific port number is automatically copied and transmitted to a monitoring/destination port. Typically, the destination port is part of the monitoring software or security application that analyzes these data packets.
The port mirroring process is generally hidden from the source and other nodes on the network.