sw1:
vlan 100
remote-span
monitor session 1 source vlan 20 rx
monitor session 1 destination remote vlan 100
sw2:
vlan 100
remote-span
monitor session 1 source vlan 21 rx
monitor session 1 destination remote vlan 100
sw3:
vlan 100
remote-span
monitor session 1 source remote vlan 100
monitor session 1 destination interface f0/12
monitor session 2 source interface port-channnel 1
monitor session 2 destination interface f0/10