Great news – now Fortigate supports exporting data flows statistics to an external server using sFlow protocol (twin of Netflow from the Cisco world). I configured it in about a minute and it just works. To collect the sFlow data I use nfdump/Nfsen , that I found to be the most stable and versatile, not to mention being the rare one supporting both Netflow and sFlow.
You first set external server IP and destination port , here it is 10.99.99.158 and UDP 7774, and then enable flow export per interface. Example follows, here I did it on Fortigate 100.
set collector-ip 10.99.99.158
set collector-port 7774
# show system interface dmz1
config system interface
set vdom “root”
set ip 10.99.99.254 255.255.255.0
set allowaccess ping https ssh snmp
set type physical
set wccp enable
set sflow-sampler enable