Status and Statistics : Switched Port Analyzer (SPAN)
 
Switched Port Analyzer (SPAN)
The SPAN feature, which is sometimes called port mirroring or port monitoring, selects network traffic for analysis by a network analyzer. The network analyzer can be a Cisco SwitchProbe device or other Remote Monitoring (RMON) probes.
Port mirroring is used on a network device to send a copy of network packets, seen on a single device port, multiple device ports, or an entire VLAN, to a network monitoring connection on another port on the device. This is commonly used when monitoring of network traffic, such as for an intrusion-detection system, is required. A network analyzer, connected to the monitoring port, processes the data packets.
The device can mirror up to four interfaces per session.
A packet, which is received on a network port and assigned to a VLAN that is subject to mirroring, is mirrored to the analyzer port even if the packet was eventually trapped or discarded. Packets sent by the device are mirrored when Transmit (Tx) mirroring is activated.
Mirroring does not guarantee that all traffic from the source port(s) is received on the analyzer (destination) port. If more data is sent to the analyzer port than it can support, some data might be lost.