EM7355 - MAC Address Assignment

IoT Modules MC/EM Series
1

Hey everyone - I’m looking for information on how the MAC address is assigned to this adapter, specifically in windows systems.

Currently all our devices are being provisioned with the same MAC address on the windows adapter. I’m not sure if this is a driver setting or a firmware setting.
HP Support is not sure where this is set either, so I’m hoping to find some help here.

Details:
Name : Mobile Broadband Connection 2
Description : HP lt4111 LTE/EV-DO/HSPA+ Mobile Broadband Module Network Device
GUID : {63EBCB87-F5AF-46B6-A257-5110985437CD}
Physical Address : 00:a0:c6:xx:xx:xx
State : Not connected
Device type : Mobile Broadband device is embedded in the system
Cellular class : GSM
Device Id :
Manufacturer : Sierra Wireless, Incorporated
Model : EM7355
Firmware Version : SWI9X15C_05.05.58.01 9902405 01

2

I don’t actually know how WIndows does this, but based on the behaviour I’ve seen in Linux I think this address is hardcoded in both firmware and driver. The firmware has some additional code to pick up whatever MAC address the driver decides to use. But that will sometimes fail, making it a safer choice for the driver to go with that well known address. I don’t know if you can make the WIndows driver pick some other address. Maybe you can in some driver setting. But it won’t be a good hardware ID in any case.

A little background:

If you look at the Linux qmi_wwan driver, you’ll find that address hard coded as “buggy_fw_addr”:
git.kernel.org/cgit/linux/kerne … wan.c#n154

The reason is simply that we want to avoid using this address, even for devices advertising it in USB decriptors. No Sierra device does that AFAIK, but the issue and the address is the same for all devices based on the same Qualcomm firmware. Note that there is nothing wrong about this. There aren’t really any technical reasons why the address can’t be the same for all devices. It is only used on the USB link between host and modem (if at all - it is completely unused in MBIM or QMI raw-ip mode). And even with multiple identical modems installed in the same host, you will still have a unique link and host network interface per modem. They could all be using the same MAC address without any conflict.

But as you note, it is sometimes confusing to provisioning software etc, which like to use the MAC address as a hardware ID. I think the real solution is to fix the provisioning software. The real hardware IDs of a mobile network adapter is one of IMEI, MEID, serial number or, if you want to identify the connection and not the modem, the SIM ICCID. The MAC address is a fake value used only for host<->firmware communcation, and willl not identify the adapter.

3

Thanks dl5162, you hit the nail on the head with the provisioning software piece. We’re pursing that route with a feature request, however that has a tail of 9+ months to get that implemented from the software manufacturer. Somehow these devices in windows when coming OEM from HP have unique MAC addresses assigned. After we format them and put our corporate image on them along with the default HP driver, the MAC address reverts to the buggy_fw address style mac.

While I agree the ultimate fix would be to identify clients with a unique guid and not by their mac address of the adapter they chose to connect with, it’s just not something we can do within our timetable.

Hoping someone might be familiar with the windows drivers and perhaps know of some kind of software switch that will allow us to set the mac, there’s nothing in the exposed advanced properties.