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Hello everybody,
I want to use a 40Mhz width channel for my 5Ghz radio here in germany.So I'm using Band Steering and the DFS channels, but I see problems regardingApple Devices like MacBooks and iMacs regarding DFSWhen I deactivate DFS the BandSteering works fine and the Apple devices uses 5 Ghz, when DFS is enable the devices uses with 95% the 2.4 Ghz band.
Is this a Apple problem or a problem regarding the Band Steering function (Steering to 5Ghz DFS channels).
Has seen someone of you the same problem.
Best regardsDavid

I am not that familiar with Apple, but the non-DFS channels in 5GHz (36-48) should also be available and work just fine.

It could be that Apple expects problems with the (more prevalent) DFS channels (52-140) and trys to "steer" you to 2.4GHz first.   It's too bad the UNII-3 band (149- 165) aren't available to you. 

The AP may actually be picking up real radar pulses and disabling those channels.

How far from a military or civilian airport are you?   Are you using higher gain antennas than came with the AP?   Are you trying to run indoors or outdoors? 

As far as I know, all Band Steering uses proprieary algorithms, and doesn't have a defined operational standard.   It may or may not have anything to do with Apple.

Worst case scenario would be outdoors, near an airport, with high gain antennas.

As Howard said the Band Steering uses proprietary algorithms.

Band steering works in the access point by directing 5 GHz-capable clients to that band. When the access point hears a request from a client to associate on both the 2.4 GHz and 5GHz bands, it knows the client is capable of operation in 5 GHz. It steers the client by responding only to the 5 GHz association request and not the 2.4 GHz request.
1) If possible capture the packets in the wireless side and check the STA is sending the Association Request in the 5Ghz.
2)Many vendors will be having the ratio in  which they band steer. For example 1:3, 1 for 2.4Ghz and 3 STAs for 5Ghz. Check the documentation of the AP for this.
3) In some APs they set threshold for probe request/associations. for example if the STA is capable of 2.4 & 5, if it keep on sending probes/association to 2.4Ghz for 10 (threshold) probes/associations it will accept even though band steering is enabled. To be precise, in Linux you can set the BSSID of the AP. The STA keeps sending requests to same radio. Hence this feature is implementation.
It all depends on algorithm. 
If STA doesnt send request then its client problem. Otherwise you might want to check the algorithm in which they implemented.

Few Links:
http://meraki.cisco.com/blog/2011/04/using-spectrum-wisely-with-band-steering/
http://www.ruckuswireless.com/on-wireless
http://www.youtube.com/watch?v=uGmfPwbs2Jg
http://www.youtube.com/watch?v=P2vIWETyWfk