Pavel, Felix thanks for the quick response. Appears that I missed the
discussion of this solution.

2012/8/23 Felix Fietkau [off-list ref]:

On 2012-08-20 5:13 PM, Pavel Roskin wrote:

quoted

On Sun, 19 Aug 2012 21:51:27 +0400
Sergey Ryazanov [off-list ref] wrote:

quoted

Hello dear all,

please tell me, why in the WDS mode, the stack creates a new interface
for each WDS station, and this interface hostapd adds to the parent AP
interface bridge? Why we couldn't simply pass this frames via AP
interface?

You may want to use a completely different IP address and netmask on the
WDS interface.  Using the AP interface would take away that option.

hostapd is not a part of the kernel.  It should be possible not to add
WDS interfaces to the bridge.

It's not just that. If the WDS station communication were done over the
AP interface, mac80211 would have to keep a table of which MAC address
is reachable behind which WDS station, which is something that the
bridge layer is supposed to do.
I've seen such a design mistake in various drivers, and I've seen the
weird quirks that this usually produces in more complex network
topologies ;)

Implementing WDS support directly in the driver (or stack) - it is
really a complex task. Several years ago, had to spend a lot of time
catching bugs in the madwifi code. But when we use virtual interfaces
and generic bridge there a few questions.
1. How to isolate the clients and hosts behind them?
2. How to tag outgoing packets with 802.1Q tags? If we do:
ip link add link wlan0 name wlan0.15 type vlan id 15
it will only tagged packets going directly to client stations, but not
to hosts behind them.

-- 
BR Sergey