How to handle multiple SSIDs with the same BSS

alan alan.schmitz
Wed Dec 23 14:17:48 PST 2009

On Wed, 23 Dec 2009 23:07:07 +0100
Witold Sowa <witold.sowa at> wrote:

> Marcel Holtmann pisze:
> > Hi Jouni,
> > 
> >>> 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.

> >>> Also looking into the register_bss callbacks, you only get the BSS
> >>> address and not the set of IE.
> >> I don't know how this mechanism is supposed to be used, but there needs
> >> to be a way for fetching more information about the BSS and BSSID by
> >> itself is not a sufficient key for identifying which BSS is being
> >> queried for (need to have BSSID,SSID pair or some other internally
> >> generated identifier which can be guaranteed to be unique).
> > 
> > Does wpa_supplicant already generate such unique BSS based identifier
> > somewhere internally? If not, it might make sense to do so.
> It doesn't AFAIK. We generate identifier for DBus usage only.
> Witek.
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