RSPAN
Remote Switch Port Analyzer or RSPAN is a type of SPAN that is used on Cisco switches that allows you to copy all traffic from a single or multiple source ports or source VLANs to a destination interface that is on a different switch. This is in contrast to SPAN which copies traffic to a destination interface on the same switch.
When using RSPAN you must to use a dedicated VLAN for your RSPAN traffic so that traffic can travel from the source switch to the destination switch. This dedicated RSPAN VLAN must be configured as an RSPAN VLAN on all of the intermediate switches that may carry it throughout the network. This is achieved by issuing the remote-span command under the appropriate VLAN configuration.
Switch1(config)# vlan 100 Switch1(config-vlan)# remote-span Switch1(config-vlan)# end
The above commands configure VLAN 100 as an RSPAN VLAN. This should be applied to the source switch, the destination switch, as well as on all intermediate switches between them. The VLAN should also be allowed on all the trunks in the path from source to destination.
Links:
https://forum.networklessons.com/t/cisco-ios-span-and-rspan/1096/89?u=lagapidis