netdev - Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

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Date:	Tue, 17 Nov 2009 14:42:39 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	netdev <netdev@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Felix Fietkau <nbd@...nwrt.org>
Subject: Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

On Tue, 17 Nov 2009 21:48:18 +0100
Johannes Berg <johannes@...solutions.net> wrote:

> A number of people have tried to add a wireless interface
> (in managed mode) to a bridge and then complained that it
> doesn't work. It cannot work, however, because in 802.11
> networks all packets need to be acknowledged and as such
> need to be sent to the right address. Promiscuous doesn't
> help here. The wireless address format used for these
> links has only space for three addresses, the
>  * transmitter, which must be equal to the sender (origin)
>  * receiver (on the wireless medium), which is the AP in
>    the case of managed mode
>  * the recipient (destination), which is on the APs local
>    network segment
> 
> In an IBSS, it is similar, but the receiver and recipient
> must match and the third address is used as the BSSID.
> 
> To avoid such mistakes in the future, disallow adding a
> wireless interface to a bridge.
> 
> Felix has recently added a four-address mode to the AP
> and client side that can be used (after negotiating that
> it is possible, which must happen out-of-band by setting
> up both sides) for bridging, so allow that case.
> 
> Signed-off-by: Johannes Berg <johannes@...solutions.net>

Looks good, maybe true four-address mode support will be available
more widely, and this will no longer be an issue.

Acked-by: Stephen Hemminger <shemminger@...tta.com>
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