This config provides info on data coming from my FWSM trusted-interface vlan destined to my internal network.
VlanXXXX is the management vlan of my 7613, VlanYYYY is the FWSM's trusted interface
mls flow ip full
ip flow-export source VlanXXXX
ip flow-export version 5
ip flow-export destination a.b.c.d 2055
ip flow ingress