"channel [21] (157) is disabled for use in AP mode"

Marty marty at heavyreckoning.com
Sun Apr 28 06:57:52 EDT 2013

On 04/28/2013 06:05 AM, Zack Buhman wrote:
> I'd like to use channel 157, as I've done in the past. I've read
> [1] that 157 is perfectly valid to use in the US. Apparently
> hostapd disagrees with this assesment.
> I'm using hostapd hostapd v2.0 [2] using the nl80211 driver on
> ath9k hardware.
> iw reg get: http://ix.io/5o7 iw list: http://ix.io/5o6 hostapd -dd
> /etc/hostapd/hostapd.conf: http://ix.io/5o8
> I'm not quite understanding how hostapd came to the conclusion that
> I can't use channel 157, and, more importantly, how I can fix
> this.
> [1]
> https://en.wikipedia.org/wiki/List_of_WLAN_channels#5.C2.A0GHz_.28802.11a.2Fh.2Fj.2Fn.29.5B13.5D
[2] http://w1.fi/releases/hostapd-2.0.tar.gz

This appears to be the important message in the debug output you listed:

channel [21] (157) is disabled for use in AP mode, flags: 0x77 NO-IBSS

I'm not up to speed on it, but it appears that while allowed for use
for other purposes, like DFS and TPS, it cannot be used for an access
point channel because no BSS in the sense an AP uses one is used on
that channel.  I think this might be because there have been
interference issues with satellite and radar in the 5-5.8Ghz band and
so use of some channels in the 5Ghz range have to be selected
dynamically to avoid interference with existing critical systems.  So
you shouldn't manually select them, but instead need a layer that
handles that dynamic channel selection.  Reference 802.11h


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