A simple SPAN (or PORT MIRROR) is
to set which port will be monitored and which port will the
sniffer attach.
from config mode
conf t
!
mon sess 1 source interface g0/22
mon sess 1 destination interface g0/24
!
exit
!
Verify with
show mon sess 1
When you are finished monitoring you
turn it off by
conf t
!
no mon sess 1
!
exit
!