HUP not changing channel

Jouni Malinen j
Mon Jun 16 14:19:21 PDT 2014

On Thu, Jun 12, 2014 at 10:06:12AM -0700, Sean Straw wrote:
> I'm working on a project which involves running a device (presently an
> ath9k_htc based one, but plans are to support another device as well) as a
> client and a host concurrently.  There is one radio, so I have to track the
> same channel # for both configurations.  The client configuration
> (wpa_supplicant) is what I'd call the primary - I have to use whatever
> frequency is necessary for connecting to the site AP and gaining access to
> the internet.  The host config (hostapd) merely needs to track the same
> channel so that both interfaces can remain up as needed.  Ideally, this
> would be automatic, but I've been working to detect channel changes on the
> client side and regenerate the hostapd and issue a HUP.

> However, hostapd doesn't appear to change channels.

That is not supported. There is ongoing work on enabling proper channel
switch announcement and with that, dynamic changes of operating channels
in AP mode.

In general, SIGHUP can be used to update only a very limited set of
parameters reliably. I consider the WPS needs (SSID and passphrase and
security policy between open and WPA2-Personal) as the only supported
use case. Some other parameters may get updated properly, but that
should not be assumed to be the case in general.

If you want to change some radio parameters, the only supported way of
doing it now is by stopping and restarting the network (either by
stopping and restarting the hostapd process or by using the
DISABLE/ENABLE control interface commands).

Jouni Malinen                                            PGP id EFC895FA

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