No beacon activity

Jouni Malinen j
Sun Feb 13 10:20:19 PST 2011

On Wed, Feb 09, 2011 at 03:19:28PM -0800, Lara Deek wrote:
> The beacons I would like machine A to capture are those of its neighboring
> APs, to identify which APs can potentially conflict with it if they are on
> the same channel. A does not capture any beacons, but only captures probe
> request (broadcast) and response messages.

Which kernel (mac80211) version are you using? Until very recently,
mac80211 filtered out received Beacon frames in AP mode. That was
changed by commit 771bbd09f7febb854dd7c30f983aa57535f9e8c9 (Feb 1). I'm
not sure I understood the setup you are using, but if this device is
indeed in AP mode, that change would be needed to receive the Beacon
frames from other APs.

> Yes, I have used another device in monitor mode (with an Ubiquiti SRC
> 802.11a/b/g MCX card with an AR5004 chipset), which captures beacons from
> sources but never from A. A has an AirMagnet
> card<>which
> has an AR5416+AR5133 ath9k supported chipset. I am not sure whether
> the issues I am facing are actually due to limitations of the 802.11n PC
> card I am using. Unfortunately, the card has no online support.

I'm not aware of any special limits like that, i.e., any AR5416-based
card should be able to work in AP mode and send out Beacon frames.

> Otherwise, I am correctly configuring hostapd on A to run in master mode.
> After running hostapd, running iwconfig on A indicates that it is in master
> mode. The only problem is that there is no beacon activity. I would
> appreciate any insight on what the problem could be.

Please verify that the driver is seeing software beacon alert (SWBA)
interrupts when hostapd is running. There is a counter for this which is
available in debugfs, e.g., in the following file

The SWBA counter should be increasing by one for every Beacon frame sent

Jouni Malinen                                            PGP id EFC895FA

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