How to handle multiple SSIDs with the same BSS

Marcel Holtmann marcel at holtmann.org
Fri Dec 25 18:29:00 EST 2009


Hi Dan,

> > > > >>> BSS 00:1a:a1:53:50:a0 (on wlan0)
> > > > >>> 	SSID: Private
> > > > >>> BSS 00:1a:a1:53:50:a0 (on wlan0)
> > > > >>> 	SSID: Public
> > > > >>> When using the wpa_supplicant D-Bus interface, every BSS can only be
> > > > >>> listed once and so we either see "Private" or "Public", but never
> > > > >>> actually both of them. How should this be handled.
> > > > >> I wasn't aware that there is this kind of limitation in the D-Bus
> > > > >> interface. It is clearly broken if it cannot include both of those
> > > > >> networks.
> > > > > 
> > > > > from what I have read so far while going through the code, it is not
> > > > > possible. The BSSID is used as unique path in D-Bus terms and because of
> > > > > that there is no way both networks could be listed at the same time.
> > > > > 
> > > > Precisely. Path of DBus object representing BSS is based on BSSID. Since
> > > > the path must be unique we can't have both networks listed.
> > > > I think that we can change a path format quite easy in the new DBus API,
> > > > but I'm afraid that changes in the old API may may brake it.
> > > > Actually, I was sure that BSSID is an unique identifier, but obviously
> > > > we need to think out something else. Is the pair of BSSID and SSID
> > > > unique? I'm not sure.
> > > 
> > > I missed the beginning of this, but the BSSID *should* be unique unless
> > > someone is spoofing their mac.  If it is two separate APs each
> > > providing the same SSID, the BSSID should be the mac and that should be
> > > unique.  If it is virtual APs providing the same SSID, the BSSID should
> > > be unique.  I apologize for missing the beginning of this, but
> > > something seems strange with the AP setup.
> > 
> > the BSSID is unique, but an access point can broadcast two different
> > SSIDs via the same BSSID.
> > 
> > This is not about the same SSID. We are talking about different SSIDs
> > from the same access point.
> 
> This used to be used for Cisco APs where the main broadcasted SSID was
> the "public" SSID (Guest SSID) and there was a second non-broadcast SSID
> using the same BSSID.  Of course, the public SSID shows up in the scan
> results unless you probe-scan for the hidden one.  Yay.

I have all variations of these Cisco APs around. When both are hidden
then you are also going to have fun. So far it is just pure luck which
one shows up first. Especially with Intel wireless cards where you
always get the full set of scan results after a probe scan.

Regards

Marcel




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