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

From: Stephen Hemminger <[email-masked]>
Date: Tue, 17 Nov 2009 14:42:39 -0800

On Tue, 17 Nov 2009 21:48:18 +0100
Johannes Berg <[email-masked]> 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 <[email-masked]>

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 <[email-masked]>