With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fnSysNetworkVlanIf
fn Sys Network Vlan If
1.3.6.1.4.1.12356.1.3.2.1.3
The interface that receives the VLAN packets intended for this VLAN subinterface.
Back to FORTINET-MIB MIB page.
IPHost Network monitor allows you to monitor fnSysNetworkVlanIf 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.