SPAN

Switched port analyzer. Quite a cool little feature here. Lets you configure what is basically traffic mirroring on select ports for transmission to a destination port (usually connected to some sort of network or traffic monitoring device).
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a008015c612.shtml


Command Reference:
1 switch
(config)monitor session [#] source [interface, remote, vlan]
(config)monitor session [#] destination [interface, remote, vlan]

RSPAN-remote switch
Switch 1
(config)vlan [#]
(config-vlan)remote span
(config)monitor session [#] source [interface, remote, vlan]
(config)monitor session [#] destination remote [vlan #]

Switch 2
(config)vlan [#]
(config-vlan)remote span
(config)monitor session [#] source remote vlan [#]
(config)monitor session [#] destination interface [#]

Show commands:
show monitor [session] [#]