FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
This article describes how to configure the Huawei E3276 USB Modem on the FortiGate and one of the most common mistakes users run into when configuring.

In order to configure the LTE Modem the following simple steps need to be followed.

1) Enable the LTE Modem on the FortiGate.
# configure system lte-modem
    set status enable
2) Attach the modem via USB.

The ‘wwan’ interface now comes up.
If the interface is still down, for the E3276 modem needs to add the following additional line:

# configure system lte-modem
    set modem-port 0

Common mistake.

One of the most common issues seen when configuring this LTE modem or others is that in addition to enabling the lte-modem, the 3G modem configuration is enabled as well:
# configure system modem
    set status enable

When both of these are enabled a conflict will be created on the USB interface the modem is connected to and will interfere with LTE messages.
Be sure that all configuration is removed from ‘config system modem’ and that the status is set to disable.
After removing everything, reboot the FortiGate in order to ensure it’s working properly.

Debugging can be done with:
# diag debug console timestamp enable
# diag debug app lted -1
# diag debug enable