RSPAN 中 reflector port 使用

you can take any free port on the switch for this, you can't use that port for anyhing else when the monitor session is enabled on it. No matter whether that port is down/down or up/up.
Reflector Port
The reflector port is the mechanism that copies packets onto an RSPAN VLAN. The reflector port forwards only the traffic from the RSPAN source session with which it is affiliated. Any device connected to a port set as a reflector port loses connectivity until the RSPAN source session is disabled.
The reflector port has these characteristics:
•It is a port set to loopback.
•It cannot be an EtherChannel group, it does not trunk, and it cannot do protocol filtering.
•It can be a physical port that is assigned to an EtherChannel group, even if the EtherChannel group is specified as a SPAN source. The port is removed from the group while it is configured as a reflector port.
•A port used as a reflector port cannot be a SPAN source or destination port, nor can a port be a reflector port for more than one session at a time.
•It is invisible to all VLANs.
•The native VLAN for looped-back traffic on a reflector port is the RSPAN VLAN.
•The reflector port loops back untagged traffic to the switch. The traffic is then placed on the RSPAN VLAN and flooded to any trunk ports that carry the RSPAN VLAN.
•Spanning tree is automatically disabled on a reflector port.
If the bandwidth of the reflector port is not sufficient for the traffic volume from the corresponding source ports and VLANs, the excess packets are dropped. A 10/100 port reflects at 100 Mbps. A Gigabit port reflects at 1 Gbps.