The port-list is a list of monitor ports that transmit identical copies of mirrored packets. The loopback-port is an unused port that is required when you mirror to a port-list. The loopback-port is not available for switching user data traffic.
Note
When you change the mirroring configuration, the switch stops sending egress packets from the monitor port until the change is complete. The ingress mirroring traffic to the monitor port and regular traffic are not affected.