USB Compatibility can be found here http://docs.fortinet.com/uploaded/files/2440/fortigate-modem-compatibility-matrix.pdf

A fortinet device does not recognise a Sierra Wireless 320U IMEI , you will need the following config

Source code

config system modem
    set status enable
    set auto-dial enable
    set connect-timeout 30
    set wireless-port 4
    set phone1 "*99#"
    set extra-init1 "at+cgdcont=1,\"IP\",\"telstra.internet\""
    set extra-init2 "at+cgdcont=1,\"IP\",\"telstra.internet\""
    set altmode disable
end
config system 3g-modem custom
    edit 1
        set vendor "Sierra Wireless"
        set model "320U"
        set vendor-id 1199
        set product-id 68aa
    nextconfig system lte-modemset status enableset apn “Telstra.internet”

Enable 4G/LTE:

#config system global
#set usb-lte enable
#end

Troubleshooting:

#diagnose sys modem detect wireless
#diagnose sys modem external-modem

diag sys lte-modem sim-info

See the device and see if its LTE or Modem

fnsysctl cat /proc/bus/usb/devices

The command output also shows the driver that FortiOS has assigned to this device (sierra_net). All this indicates that FortiOS has identified the modem and that it is supported as a modem and not as a USB storage device.

The last interface is a sierra_net interface, and it is an Ethernet-like interface, supported by the FortiOS LTE daemon.

Create a Policy allowing outbound through the Modem

Change the static route to 0.0.0.0 via Modem

Make sure DNS is set on Google

####### The below is the new 6.2 guide but it doesn’t work with 320U card ( its Modem not LTE modem )

https://docs.fortinet.com/document/fortigate/6.2.0/new-features/576705/direct-ip-support-for-lte-4g