APs and multiple BSSID support (OT?)

Bob Carlson rjc at sigpro.com
Wed Feb 7 11:53:56 EST 2007


> -----Original Message-----
> From: Bryan Kadzban [mailto:bryan at kadzban.is-a-geek.net]
> Sent: Wednesday, February 07, 2007 5:10 AM
> To: bob.carlson at sigpro.com
> Cc: 'Jouni Malinen'; hostap at shmoo.com
> Subject: Re: APs and multiple BSSID support (OT?)
> 
> Bob Carlson wrote:
> > The problem with mult. SSID/BSSIDs is that there is no way to make
> > the hardware aware of 2 different BSSIDs for things like timing
> > derived from the beacons.
> 
> Your multiple-BSSID APs don't send out different beacons for each
> virtual BSSID?  Ours do (Cisco 1100s and 1231s).  I suspect it's an
> option in the AP setup, but I'm not sure why you'd turn that option off.

On the Ciscos, multiple BSSIDs can be enabled or not. When enabled, I
believe they send a beacon for each BSSID in all cases. Since they come
from the same radio and mac, certain items will always be in sync, the
channel of course, the TSF, supported rates, WMM, etc. At least I believe
this pretty much has to be the case. My hardware, I'm pretty sure, can only
be set up to notice one set of beacons, even though I am connected to two
BSSIDs. It is the timing and WMM I am most worried about, but there may be
other subtleties of which I am ignorant. As long as the timing between the
BSSIDs is the same, I think I should be alright. If the BSSIDs are on
different APs, I have little confidence that it would work, since the HW
would not be aware of one of the beacons. Luckily I do not need to support
power same mode or things would get MUCH more complicated.

I need to support 2 virtual clients in 3 cases. Case 1 is 1 SSID/1 BSSID/1
AP. That's working. Second is 2 SSID/1 BSSID/1 AP. This should be a pretty
straightforward enhancement of the first case. Third is 2 SSID/2 BSSID/1
AP. That's the one I am worried about. Another case, 2 SSID/2 BSSID/2 AP, I
don't believe I can support. I might also see 1 SSID/2 BSSID/2 AP. I don't
ever want to connect the virtual clients to 2 different APs in this case
either. I believe 1 SSID/2 BSSID/1 AP is not legal or reasonable.

Cheers, Bob

> 
> > That's a long winded explanation for a simple need. Because I can
> > only successfully connect to 2 different BSSIDs if they are supported
> > by the same physical AP,
> 
> I guess I don't see why this is necessary from your explanation.  It
> should work whether your client is connecting to two BSSIDs on one AP or
> on two APs; the client shouldn't care.
> 
> Unless you mean that a single client radio can't operate on multiple
> frequencies at once?  In that case, just look at the channel number
> given in the beacons, and refuse to connect to multiple BSSIDs that are
> on different channels.  Do the same for other parameters that affect
> whether your code works or not (e.g. maybe DTIM interval matters).





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