>
> > On Sun, Nov 14, 2021 at 10:40:28PM +0100, na...@poczta.fm wrote:
>> Hi misc@,
>>
>> While testing the U-blox MPCI-L210 LTE modem on OpenBSD -current
>> (the modem is attached as a cdce(4) device, the router mode is enabled;
>> other modes are also available), I noticed that the automatic configuration
>> via DHCP works correctly, but the MAC address assigned to the corresponding
>> cdce0 network interface is different from the MAC address reported by
>> lsusb -v. Unfortunately, due to this mismatch, incoming Ethernet frames
>> having the actual MAC address of the device set as the destination address
>> in the header are dropped by the kernel in the ether_input() function
>> (/src/sys/net/if_ethersubr.c).
>>
>> Based on an analysis of the source code (/sys/dev/usb/if_cdce.c) and the
>> results of the subsequent experiments, I was able to confirm that the cdce
>> driver is unable to get the MAC address of the device (in particular,
>> the usbd_get_string_desc() function returns USBD_STALLED instead of
>> USBD_NORMAL_COMPLETION), and as a result, a semi-random fake Ethernet
>> address is set:
>>
>> -----------------------------------------------------------------------------
>> 306 if (!ethd || usbd_get_string_desc(sc->cdce_udev, ethd->iMacAddress, 0,
>> 307 &eaddr_str, &len)) {
>> 308 ether_fakeaddr(ifp); // <---- Set a semi-random MAC
>> address
>> 309 } else {
>> -----------------------------------------------------------------------------
>
> Can you find out what happens on Linux?
>
> Their cdc_ether driver seems to be doing exactly the same thing. So with
> this driver you would also end up with a random MAC if the device fails
> to respond to a mac address query. In this case I have no idea what else
> could be done apart from using the workaround you have already found.
>
> But Linux has more CDC sub-drivers than we do, and runs some devices in
> specialized modes.
> Perhaps Linux performs a mode switch and uses a different driver for e.g.
> MBIM mode? If that is the case then we could change our drivers to try to
> switch this device into a mode where it works better.
>
>
Hi Stefan,
Thank you for your prompt reply.
Good point -- I remember that I tried to use this modem on Linux some time ago
and it worked with no noticeable issues. I will take a closer look again on
Friday this week, and I will summarize my findings in my next email.
Best wishes,
Andrzej
