With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fnSysSesCount
fn Sys Ses Count
1.3.6.1.4.1.12356.1.10
Instantaneous session count
Back to FORTINET-MIB-280 MIB page.
IPHost Network monitor allows you to monitor fnSysSesCount on Fortinet device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Fortinet WAN extenders right now.