Troubleshooting Tip: Modems on a FortiGate with a USB port

The installed modem must be able to understand standard Hayes AT commands. This ensures proper communication and configuration between the modem and the FortiGate.

• The issue may be the capability and reliability of the modem to connect to the remote modem. Fortinet has tested KeySpan and Wiretek USB-to-serial converters, versions 1.1 and 2.0 USB-to-Modem adapters.
• If the modem dials but does not connect, there may be a compatibility issue between the modem and the remote modem that attempted to connect.
• Disconnect the modem from the FortiGate, and try connecting using the preferred communication software, such as HyperTerminal or ProComm, and configure it to manually dial the provider.
• If a driver is installed for this modem on the computer, the modem may receive an initialization AT string through the driver without the intervention and/or knowledge.
• When the modem is connected to the FortiGate, this initialization string is not sent to the modem.
• If this string is required to obtain a successful modem connection, configure the modem so that the AT register values are preset upon power-up.

To determine whether the modem is configured properly to connect to a remote modem.

1. Power-cycle the modem, and communicate with it directly using the COM port. Do not select a modem type within the serial communication software.
2. Establish a modem connection manually by typing the ATDTxxx command, where xxx represents the phone number.
3. Confirm a successful PAP PPP connection, for example, Windows Dial-Up Networking from the PC.

If the connection is successful, the modem is configured properly. Connect the modem to the FortiGate unit, and retest.

Related article:
Technical Tip: How to view the 3G/4G supported modem list