use of WLAN_EXT_CAPA8_OPMODE_NOTIF in hostapd/wpa_supplicant

Atul Joshi Atul.Joshi
Tue Apr 7 02:54:50 PDT 2015

Thanks for the answer but why should this be added to assoc request.
For HT this is not defined in the spec and with VHT, this is set for SCS,

For non VHT case, should this not be set to 0? (as it is not defined in the 11n spec)


-----Original Message-----
From: Johannes Berg [mailto:johannes at] 
Sent: Tuesday, April 07, 2015 2:14 PM
To: Atul Joshi
Cc: hostap at
Subject: Re: use of WLAN_EXT_CAPA8_OPMODE_NOTIF in hostapd/wpa_supplicant

On Mon, 2015-04-06 at 09:31 +0000, Atul Joshi wrote:
> Hi,
> Hostapd/wpa_supplicant  gets the driver capabilities as a part of 
> initilisation.
> As a part of this procedure, even extended capabilities are passed by
> mac80211/cfg80211 to the user space.
> I  can see that while other extended capabilities are filled in, in 
> main.c in mac80211 WLAN_EXT_CAPA8_OPMODE_NOTIF is also  set (it is 
> used to set bit 6 of octet 7)
> Hostpad/wpa_supplicant does not read this and just stores it, 
> resulting in extended_capabilities IE in various messages to have 8 
> octets and this the last octet set to 0x40.
> Why is this bit set and how is it supposed  to be used in 
> hostapd/wpa_supplicant?

It's not supposed to be used there, but it's a protocol bit that the remote side needs to know. As such, the kernel passes out all the bits that it supports by itself (without supplicant involvement) so that they can be sent to the AP in the assoc request frame etc.


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