Technical Tip: USB Tethering using Mobile Phone on FortiGate

USB Tethering is the process of sharing the internet connection of a mobile device to another device, like using a USB cable.

In this deployment, the mobile device is connected directly to FortiGate using a USB cable. 

Enable USB Tethering on the mobile phone. Different models of mobile phones have different ways to enable USB Tethering. Check the mobile phone manual to know how to enable this service.

Viewing the 3G/4G supported modem list on FortiGate.

To verify the supported modem list: Navigate to Network -> Modem in the GUI.

Select Configure modem to display the complete list of supported modems.

Ensure to download the latest list from FortiGuard, as this list is maintained through FortiGuard updates.

Use the search function within this list to locate specific modem models.

Check if the mobile device is connected and make sure that the mobile phone is detected with 'Driver=rndis_host'.

FortiWiFi-60E # fnsysctl cat /proc/bus/usb/devices

T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  4 Spd=480  MxCh= 0

D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1

P:  Vendor=0e8d ProdID=2004 Rev= 2.23

S:  Manufacturer=INFINIX MOBILITY LIMITED

S:  Product=Infinix X6815B

S:  SerialNumber=081XXXXXXXXXXXXXX

C:* #Ifs= 2 Cfg#= 1 Atr=80 MxPwr=500mA

A:  FirstIf#= 0 IfCount= 2 Cls=e0(wlcon) Sub=01 Prot=03

I:* If#= 0 Alt= 0 #EPs= 1 Cls=e0(wlcon) Sub=01 Prot=03 Driver=rndis_host

E:  Ad=82(I) Atr=03(Int.) MxPS=   8 Ivl=32ms

I:* If#= 1 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=rndis_host

E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms

E:  Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms

Enable LTE modem on FortiGate using the below command. This will enable the interface 'wwan'.

There are instances where 'wimax-4g-usb' should be enabled as well.

config system lte-modem

    set status enable

end

config system global

    set wimax-4g-usb enable

end

Interface 'wwan' will get an IP address and default gateway via DHCP from the mobile phone USB tethering. 

FortiWiFi-60E # get router info routing-table all

Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP

       O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       V - BGP VPNv4

       * - candidate default

Routing table for VRF=0

S*      0.0.0.0/0 [1/0] via 10.153.176.187, wwan, [1/0]

S       10.81.3.170/32 [254/0] is a summary, Null, [1/0]

C       10.153.176.0/24 is directly connected, wwan

Note that there is a known issue 1181444 (Resolved issues) related to USB-Tethering failing to work on FortiGate 91G when configuring it as a WWAN connection.

This issue has been resolved in:

• v7.4.9 (already available).
• v7.6.5 (already available).
• v8.0.0 (scheduled to be released in April 2026).

The timelines for firmware releases are estimated and may be subject to change.