With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fgHaStatsSesCount
fg Ha Stats Ses Count
1.3.6.1.4.1.12356.101.13.2.1.1.6
Current session count of specified cluster member
Back to FORTINET-FORTIGATE-MIB MIB page.
IPHost Network monitor allows you to monitor fgHaStatsSesCount 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.