Newbie questions, starting point

[Dan Williams]

On Mon, 2016-05-02 at 11:31 -0400, Neil Cherry wrote:
> If this is the incorrect place to ask, please point me to the correct
> place.
> 
> I have a Netgear 341u modem and I'm trying to use it as a backup
> connection.
> I'm not sure how to begin. The modem works fine under Win7 but I want
> to
> use this with Linux (playing with a Pi at the moment but I have other
> systems). Instead of asking a lot of dumb questions can someone point
> me
> to the theory of operation? So I can at least get a clue how the QMI
> and
> the modem connect to the LTE network (has to be LTE, not 3G). So far
> I
> can see the modem and at one point I managed to get as far as
> dhcpclient
> (got a 169.x,y.z, yup failed to talk to the dhcp server). I've since
> lost
> my way.

Not all devices implement a DHCP client in firmware, and not all
devices even attempt to emulate ethernet.

What's likely happened with your 341U is that it defaults to QMI's "raw
IP" mode which doens't bother with the faked ethernet framing, but just
passed IP packets back and forth.  There's support for this mode in
recent versions of libqmi, the kernel's qmi-wwan driver, and
ModemManager.  You can try to recover ethernet emulation (802.3 mode)
with qmicli like so:

qmicli -d /dev/cdc-wdm0 --wda-set-data-format=802-3

at which point DHCP might start working again.  Very recent
ModemManager versions will try to do this automatically.

Let us know if that helps, otherwise we can dig a bit deeper.

Dan