Re: [Bridge] Hardware requirements for bridging wired+wireless together

[Simon Barber <simon@superduper.net>]

Unfortunately the concept of a native 802.11 interface got removed from 
the kernel a few months ago. This is a great shame, since it means that 
it's now impossible to write qdiscs that work correctly for WiFi when 
using 802.11's own priority mechanisms as well. The wlan0 interface is a 
virtual interface that works with 802.3 format frames.

Simon


On 05/19/2010 02:01 PM, Umar Qureshey wrote:
>>> -----Original Message-----
>>> From: John W. Linville [mailto:linville@tuxdriver.com]
>>> Sent: Wednesday, May 19, 2010 12:20 PM
>>> To: Umar Qureshey
>>> Cc: Stephen Hemminger; bridge@lists.linux-foundation.org
>>> Subject: Re: [Bridge] Hardware requirements for bridging
> wired+wireless together
>>>
>>> On Wed, May 19, 2010 at 10:15:35AM -0700, Umar Qureshey wrote:
>>>
>>>> What about bridging in Ad-Hoc mode?  Would that technically work?
>>>
>>> No.
>>>
>>>> I guess what I am trying to figure out is why bridging would work
> in WDS mode?  What is it about that mode that allows bridging to work?
>>>
>>> It has to do with the MAC-layer addressing on wireless LANs.
> Wireless
>>> frames can use 2, 3, or 4 MAC addresses to identify the transmitter,
>>> receiver, sender, and destination.  For most frames and most modes,
>>> 3 MAC addresses are used.  The FromDS and ToDS bits in the header
>>> are used to allow one of the MAC address fields to specify either
>>> the transmitter and sender or the destination and receiver.  This is
>>> sufficient for non-bridged cases since the wireless station is either
>>> an endpoint of the communication or possibly a router (and therefore
>>> a Layer-2 endpoint).
>>>
>>> WDS (or 4 address) mode removes this limitation by using 4 MAC
>>> addresses to identify all 4 roles independently.  So, the wireless
>>> station is able to forward frames received off the air to the
>>> appropriate destination with the correct sender information intact.
>>>
>>> mac80211-based devices can have interfaces created with support for
>>> 4 address mode using the iw command.  For this to work, your AP has
>>> to be willing to accept and forward those frames appropriately --
>>> some do, others don't.  This is only supported for "managed" mode
>>> interfaces AFAIK.
>>>
>>>> If one were to try to modify the kernel code to allow MAC-level
> NAT, which area of the kernel code would one look at?
>>>
>>> netfilter -- I thought there was already some ebtables code to
>>> do this...?
>>>
>>> John
>>> --
>>> John W. Linville		Someday the world will need a hero, and
> you
>>> linville@tuxdriver.com			might be all we have.
> Be ready.
>
> Ok thanks for the explanation about WDS.
>
> Stepping back into a Linux box with two interfaces, one Ethernet (eth0)
> and one wireless 802.11 (wlan0), and one bridge (br0) that bridges these
> two interfaces together:
>
>
>                             br0
>                              |
>                   eth0-------+-------wlan0
>
> Can one say that, in this case, the bridge is not working because br0 is
> passing to wlan0 Ethernet 802.3 frames which (naturally) the wlan0
> interface has no idea how to decode?
>
>
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