netdev - Re: cdc_ncm driver padding problem

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Message-ID: <87h99guzem.fsf@miraculix.mork.no>
Date:   Fri, 16 Sep 2016 08:33:37 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     Marek Brudka <mbrudka@...il.com>
Cc:     netdev@...r.kernel.org, linux-usb@...r.kernel.org,
        Enrico Mioso <mrkiko.rs@...il.com>
Subject: Re: cdc_ncm driver padding problem

> ==From: Marek Brudka <mbrudka@...il.com>
..
> ==The bad thing is DHCP. It seems, that cdc_ncm driver somehow consumes DHCP
> ==replies. I had to manually setup wwan0 interface as well as routing
> ==using the result
> ==of Hayes command
> ==
> ==AT^DHCP?
> ==^DHCP:
> ==EC684764,F8FFFFFF,E9684764,E9684764,356002D4,366002D4,43200000,43200000
> ==OK

Are we sure that this firmware supports DHCP?  It's not uncommon for
modem firmwares to lack such support, and I find this a much more likely
explanation than the driver somehow messing up the DHCP replies while
letting other packets through.

Unfortunately there is no easy way to tell for sure if a specific
feature is enabled or not in a specific firmware.  Is it possible to get
a snoop from Windows while connecting, using the modem in the same mode?
That would tell us whether the Windows software depends on DHCP or is
using the AT^DHCP command.

Bjørn