Configuring Quectel EC25-EUX 4G LTE modems in OPNsense

Introduction

We now ship our OPNsense routers with Quectel EC25-EUX 4G LTE modems. The Huawei modems we used before have become rare and very expensive because of the US sanctions against Huawei.

This article shows how to configure a Quectel EC25-EUX modem in OPNsense, and what changes compared with the Huawei ME909s-120 modem you may already know.

What changes compared with the Huawei ME909s-120

The configuration is the same, except for two details.

1. The serial port of the modem

• /dev/cuaUx.3 for the Quectel EC25-EUX and the SIMCom SIM7600G-H;
• /dev/cuaUx.0 for the Huawei ME909s-120.

x is the number of the modem. With a single modem in the router, which is the most common case, x is 0: the port of the EC25-EUX is then /dev/cuaU0.3.

2. The initialisation string (Init String)

Configuration in OPNsense

In the OPNsense web interface, open Interfaces > Point-to-Point > Devices and add a device:

• Link Type: PPP;
• Link interface(s): /dev/cuaU0.3, listed as "Quectel EC25-EUX";
• Description: any name, for example the name of the carrier;
• Username, Password and Access Point Name (APN): the values given by your carrier (the example below uses the French carrier Free);
• Phone Number: *99#;
• Init String (in the advanced options): leave it empty.

Save, then assign this device to an interface in Interfaces > Assignments.

Here is the complete configuration of a Quectel EC25-EUX modem in OPNsense (click to enlarge):

The 4G link drops after a few seconds?

A user reported a backup 4G link that worked for about ten seconds, then dropped and could not come back up. His OPNsense was running in a Proxmox virtual machine on the appliance.

We have not seen any problem with the Quectel EC25-EUX when OPNsense is installed directly on the hardware. If OPNsense or pfSense runs in a virtual machine, first test the modem by booting OPNsense in live mode (VGA or serial images): you will then know whether the problem comes from the modem or from the virtualisation.