Setting NetFlow

enable
configure terminal
ip cef                                      //enables Cisco Express Forwarding
ip flow export source vlan3
ip flow-cache timeout active 5              //active flows [minutes]
ip flow-cache timeout inactive 30           //inactive flows [seconds]
ip flow-export version 9
ip flow-export destination a.b.c.d 2055
interface FastEthernet0/0
ip flow ingress
ip flow egress
end

Use NetFlow version 5 if v9 unavailable:

interface FastEthernet 0/0
ip route-cache flow
exit
ip flow-export destination a.b.c.d
ip flow-export source vlan3
ip flow-export version 5
ip flow-cache timeout active 5
ip flow-cache timeout inactive 30
snmp-server ifindex persist

Note that older versions (eg. Catalyst 6500) used a different command for setting cache timeout:

mls aging long 300
mls aging normal 32

In this case, also make sure to set the flow mask:

mls netflow interface
mls flow ip interface-full

For CatOS device:

set mls agingtime long 300
set mls agingtime 32