Introduction to Traffic Mirroring
Switched Port Analyzer (SPAN), which is also called port mirroring, or traffic mirroring enables you to monitor network traffic passing in, or out of, a set of ports. You can then pass this traffic to a destination port on the same router.
Traffic mirroring copies traffic from one or more source ports and sends the copied traffic to one or more destinations for analysis by a network analyzer or other monitoring device. However, traffic from one source port can be copied to only one destination port. Traffic mirroring does not affect the flow of traffic on the source ports, and allows the mirrored traffic to be sent to a destination port.
For example, you need to attach a traffic analyzer to the router if you want to capture Ethernet traffic that is sent by host A to host B. Traffic between host A and host B is also seen on the destination port.