I am trying to attach a network interfaces (Ethernet Port and mobile Broadband) to my Pi through USB. When I do this on my Pi 1 or Pi Zero it shows up and works without a hitch, but with the exact same installation on the same SD card on a Pi 3, the interfaces do not work.

On the Pi 3, they are detected as a USB devices but do not show up when I query using commands like ip and ifconfig, even ifconfig -a.

I noticed that when attempting this on the Pi 3, the output from dmesg lacks the lines containing register 'asix' at usb-xxxx:xx:xx-x.x CDC_Ethernet Device ... (for the USB Etherne)
register 'cdc_ether' at usb-xxxx:xx:xx-x.x CDC_Ethernet Device ... (for the mobile broadband)

If it's relevant, I have removed the Pi 3's Ethernet port in order to slim down its profile.

Why is the same installation behaving differently on different Pis?

  • Paste into the question the output of lsusb when the ethernet dongle is attached. If the command is not found, sudo apt install usbutils.
    – goldilocks
    Apr 29 '19 at 22:21

It seems for me that you try to use OTG Gadget ether mode. This mode emulates a USB connection as ethernet connection so you can use it like a normal network connection. This only works if the USB port is direct connected to the USB on-board device. Only on a Raspberry Pi Zero and Pi Zero W is it the case. I don't know but it seems also be the case with a Raspberry Pi 1.

A Raspberry Pi 3B has more than one USB port so it uses internal an additional USB hub to split the one USB port from the on-board device. This is the reason why OTG Gadget mode doesn't work with a RPi 3B. It cannot manage a USB hub.

To have a wired ethernet connection with a RPi 3B just use its ethernet port. Btw. this ethernet port is also connected to the USB hub and shares its bandwidth with other connected USB devices.

  • You should be able to use a USB ethernet dongle on any model. Telling someone to just use the eth jack is not really a good answer...
    – goldilocks
    Apr 29 '19 at 22:20
  • @goldilocks The question was "Why is the same installation behaving differently on different Pis?". Do you mean the side note isn't a good answer because the other end may not have an ethernet port? Using an USB ethernet dongle is of course a better answer if it was asked ;-). Thanks for the idea. I will update my answer ...
    – Ingo
    Apr 29 '19 at 22:35
  • @goldilocks I'm just a bit unsure: where and how do you want to use a USB ethernet dongle in conjunction with a RPi 3B to be used for Gadget mode?
    – Ingo
    Apr 29 '19 at 22:43
  • The OP never mentions gadget mode (cdc_ether is not specific to that). Why s/he wants to use a dongle on a board that already has an ethernet jack of course remains a mystery...
    – goldilocks
    Apr 30 '19 at 2:40
  • @goldilocks Ah.. now it gets clearer. I misunderstood "attach a network interface (Ethernet Port) to my Pi through USB". I don't read that to use an USB/WiFi dongle. I read that to use an USB connection to emulate ethernet - what's doable with Gadget mode. And with this I confused cdc_ether with g_ether Raspberry Pi Zero OTG Mode.
    – Ingo
    Apr 30 '19 at 8:18

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