hostapd + channel bonding + 5GHz

Jouni Malinen j
Mon Feb 21 07:57:28 PST 2011

On Thu, Feb 17, 2011 at 05:40:14PM -0800, Lara Deek wrote:
> The ht_capab parameter in hostapd.conf enables 40MHz operation
> ([HT40-][HT40+]). I understand hostapd enables channel bonding only if there
> will be no channel/bandwidth overlap with neighboring APs (802.11n: scan for
> overlapping BSSes before starting 20/40MHz channel). Is there some way where
> I can control 40MHz vs. 20MHz operation myself without it being censored by
> hostapd?

Not without modifying the source code. hostapd will enforce 20/40 MHz
coexistence rules based on the mandatory standard requirements.

> Basically, I just want to be able to control channel bandwidth and operating
> channel using "iw dev wlan1 set freq 5745 HT20/HT40-/HT40+" while hostapd is
> running, and without being censored by hostapd.

Changing channel in that way does not work in general regardless of the
HT40 limitations. You cannot just assume that multiple programs can
control the same radio at the same time. Channel changes will need to be
initiated by hostapd so that all the needed information (e.g., Beacon
frame template and Probe Response frames) get updated properly.

> Given my hardware capabilities, I should be able to channel bond every
> channel with its adjacent channel. Hostapd restricts channel bonding to
> particular channels. Is there a reason for that? And how can I remove that
> restriction?

Yes, IEEE Std 802.11n-2009 requires this. Obviously, you can disable the
checks in the source code, but please do not expect to get any support
for that from this mailing list.

> Furthermore, according to the kernel logs, my EEPROM is set to US 0x3a (CRDA
> updates the regulatory domain for my card I guess). Is this the reason why
> the UNI-2 band is labeled as "(passive scanning, no IBSS, radar detection)"?

Yes, the UNII-2 band requires support for DFS and radar detection in US.

> I want to ask if this is a limitation set by the ath9k driver, and not my
> actual hardware. I would like to be able to use those channels to do DFS,
> and was wondering if that was a software vs. hardware limitation.

ath9k does not yet support radar detection and until support for that
gets added, we cannot enable those channels.

Jouni Malinen                                            PGP id EFC895FA

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