Core issue
The Switched Port Analyzer (SPAN) feature, sometimes called port mirroring or port monitoring, selects network traffic for analysis by a network analyzer such as a SwitchProbe device or other Remote Monitoring (RMON) probe.
Resolution
It is normal to show the port as up/down monitoring, as long as it is functioning properly. Sometimes when you configure a monitor (SPAN) session, the destination interface shows the down status (monitoring) by design.
The port state is shown in this state to make it evident that the port is currently unusable as a production port. The SPAN session's destination port will always show up as up/down due to the fact that it does not take ingress traffic.
For detailed information, refer to the Characteristics of Destination Port section of Configuring the Catalyst Switched Port Analyzer (SPAN) Feature.
