Ethernet-briding a MBIM-interface

Bjørn Mork bjorn at
Tue Oct 28 00:41:56 PDT 2014

Markus Gothe <nietzsche at> writes:

> The rationale for having a null mac adress as the ethernet source
> adress would be nice to know.

This just wasn't given much thought.  I couldn't imagine where it would
make a difference, and not copying anything seemed like slightly less
work than copying something which wouldn't matter anyway. The driver
give the frames to usbnet_skb_return() which does eth_type_trans() on
them.  This pulls the ethernet header from the skb after looking at the
h_proto and h_dest fields.  I obviously didn't think about what happens
to frames being snooped or bridged...

> Wouldnt it be better to keep it the same as the ethernet destination
> adress (like some CDC ECM implementations)??? This is afaik to be
> considered a bug. :-)

Yes, that would be more consistent also with the IFF_NOARP frames coming
from the modem.  I believe we can change this if you can point to any
use case where it actually matters.  I'm not sure I care enough to try
to push the change without any justification.

Is bridging such a use case?  Would it sort of work if the source
address was saner?


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