Query: can wpa_supplicant set up an ad-hoc network

Dan Williams dcbw
Wed Oct 21 10:52:52 PDT 2009

On Mon, 2009-10-19 at 11:14 +0800, Soh Kam Yung wrote:
> On Sat, Oct 17, 2009 at 12:08 AM, Dan Williams <dcbw at redhat.com> wrote:
> >
> > Yes.  There is no real difference between starting and joining an adhoc
> > network.  Except a scan is done first (usually in the driver) to
> > determine whether there is an existing IBSS with that SSID and security
> > settings, and if so, that IBSS's BSSID is used.
> >
> > Remember, ad-hoc is *ad-hoc*.  There's no central controller to say who
> > can join the network and who cannot.  The only access restriction is by
> > SSID and encryption key.
> >
> > Is there some specific reason you are thinking you need to distinguish
> > between the operations?
> >
> > Dan
> Dan,
> It's more of trying to understand how an ad-hoc network works.  Thanks
> for the info.
> One more question: if the initial scan does not reveal an existing
> IBSS and one is created instead by wpa_supplicant, how is the RF
> channel selected?  Is this at random or are there specific rules that
> determine which channel will be used?

Again, it's usually the *driver* that handles IBSS creation after the
scan, not the supplicant.  The RF channel is either auto-selected by the
driver, or you can specify a "frequency=" option in the supplicant's
network block to lock the IBSS to a channel of your choice.  If the
driver does not honor that channel after creating the new IBSS, then
it's a driver bug that needs to be fixed in the kernel.

> Is there a wpa_supplicant option to configure the channel to be used for a IBSS?

I believe it's 'frequency=2412' where of course you replace '2412' with
your desired channel center frequency in MHz.  We can't use channels
there, because channels overlap depending on your band.


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