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On Sun, Jan 30, 2011 at 07:49:35PM +0000, mike cloaked wrote:
> I have a question for any wireless expert who can help.
> 
> At home I have two wireless access points - one upstairs and one
> downstairs - to give a good signal anywhere in the house.
> 
> What I would like is to have a seamless wireless access from any
> laptop whether mine or a visitor with the appropriate encryption
> password.
> 
> Now my thinking is that using the *same* ssid and encryption protocol
> and password for both APs should do the trick nicely - so that is how
> I have things set up (with different channel for each AP's output) and
> indeed if I power up a laptop running F14 upstairs it connects nicely
> with a lovely strong signal - but if I then go downstairs and boot the
> same machine then it tries to connect to the upstairs AP despite the
> nearest signal about 10 feet away being a great deal stronger!   So
> the system tries to connect to the last AP it connected to even if a
> local signal is stronger - this is illogical behaviour and it is not
> clear if NetworkManager or wpa_supplicant is the culprit - or if I am
> not supposed to expect things to work that way!

Roaming and initial AP selection are really different topics.
Neither is as simple as some of the responders have asserted.

For roaming "seamlessly", simply using the same ssid and encryption
info won't matter much if the AP's aren't bridged.  Most consumer
APs out of the box use a routed NAT configuration.  This means that
when you switch between APs you will get a different IP address and
connection disruptions will result.  To avoid that, you need to make
sure the APs are bridging between wireless and ethernet, and further
you must ensure that both APs plug into the same bridged segment
on the ethernet side.  Somewhere on that network there needs to be
a single (or several coordinated) DHCP servers so that the same IP
address is equally valid on the wireless sides of either AP.  In the
best cases the APs will runn IAPP or something similar to smooth the
wireless handoffs between the two APs, but in practice that is not
entirely essential.

As for the inital AP selection...you assert that it is illogical to
select an AP you know over a stronger AP you may not know.  I'm not
sure I agree.  So long as the known AP remains serviceable, there is no
particular reason to switch to another AP simply because he registers
a stronger signal.  In a perfect world you could easily determine
which AP is "better" simply by the signal strength of a beacon,
but in reality a number of factors can effect real world "better"-ness.

I would only consider the AP selection issue a bug if NM insists on
using an unreachable AP even when the other is reachable.  In either
case, if you want to roam between the APs you should ensure that
they are both bridging the wireless connections to the same ethernet
subnet.[1]

John

[1] There are other potential configurations for roaming, including
mobile IP and the like.  If you (i.e. anyone reading) feels like
trying to explain them in an email then feel free. :-)
-- 
John W. Linville		The truth will set you free, but first it will
[email protected]			make you miserable. -- James A. Garfield
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