router#enable
Password:*****
router#configure terminal
router-2621(config)#interface FastEthernet 0/1
router-2621(config-if)#ip route-cache flow
router-2621(config-if)#exit 
router-2621(config)#ip flow-export destination 192.168.9.101 9996
router-2621(config)#ip flow-export source FastEthernet 0/1
router-2621(config)#ip flow-export version 5
router-2621(config)#ip flow-cache timeout active 1
router-2621(config)#ip flow-cache timeout inactive 15
router-2621(config)#snmp-server ifindex persist
router-2621(config)#^Z
router#write
router#show ip flow export
router#show ip cache flow

!
! Step 1: Enabling NetFlow
!
! Note: For PRTG we need NetFlow versions 5 or 9,
!       no other NetFlow version is supported currently
!
<input>ip flow-export version 5</input>
! or
! ip flow-export version 9
!
! Note: we recommend these values for the timeouts
!
! timeout active value is in minutes
<input>ip flow-cache timeout active 5</input>
!
! timeout inactive value is in seconds
<input>ip flow-cache timeout inactive 10</input> 
!
! Step 2: Setting the target address for NetFlow Packets:
!
! Replace 10.0.0.200 with the IP address of your machine running PRTG
! Replace 9991 with another port number of your choice if desired
!
<input>ip flow-export destination 10.0.0.200 9991</input>
!
! Step 3: You can optionally send all NetFlow packets to one other machine, too
!
<input>ip flow-export destination 10.0.0.201 9991</input>
!
! Step 4: Create a "NetFlow Sensor" in PRTG (V7 or later) and enter the port number set above
!
! That's it