With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fgHaStatsSerial
fg Ha Stats Serial
1.3.6.1.4.1.12356.101.13.2.1.1.2
Serial number of the HA cluster member for this row
Back to FORTINET-FORTIGATE-MIB MIB page.
IPHost Network monitor allows you to monitor fgHaStatsSerial on Fortinet device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Fortinet switches right now.
