Is wpasupplicant 0.7.3-6 compatible with 5Ghz band steering?

Marc MERLIN marc
Sat Mar 31 11:24:22 PDT 2012


Thank you for your answer.

On Sat, Mar 31, 2012 at 08:43:42PM +0300, Jouni Malinen wrote:
> On Sat, Mar 31, 2012 at 08:10:57AM -0700, Marc MERLIN wrote:
> > My company recently turned on band steering to redirect 5Ghz capable clients
> > from 2.4Ghz to 5Ghz.
> > 
> > This is causing no end of trouble for my 5300AGN linux client.
> It is a bit unfortunate that some AP vendors have introduced this type
> of proprietary functionality on their own without going through proper
> standardization and just hoping that stations behave in the way that
> works with their not necessarily even publicly documented mechanism..
Yeah, the more things change...

Now, can you quickly correct or confirm my understanding of wpa_supplicant?
I'll bef for your patience with my questions since I'm somewhat of a newbie
in this field.

I was surprised that I had to use it to connect to an unencrypted
network. I thought the driver by itself would enumerate the APs available
and pick the best one.
When signal strength dipped too low, I thought the driver would then itself
rescan and find the next best AP with best signal.

However, if I didn't use wpa_supplicant and just used iwconfig to connect
(again, this is an unencrypted network, so I can do that), I noticed the
driver picked a crappy and far away 2.4Ghz signal (30/70) instead of the AP
it was sitting right next to.

So, does it mean that the driver is too dumb to pick the best AP, and it
does require wpa_supplicant to enumerate the APs and pick the best one?

Then, do you have an idea why wpa_supplicant would forcibly disconnect from
a 5Ghz 70/70 signal to go seek a 2.4Ghz signal?
Is it hardcoded to always pick 2.4Ghz if it finds it? 
If so, can that be turned off?
Is disconnecting from 5Ghz to connect to 2.4Ghz even though auth was denied
on 2.4 a bug, or a problem in the protocol?

And to get the basics right: does linux wireless actually need
wpa_supplicant to find the closest AP and manage handoffs when moving
laptops around? Does it mean the driver can't do it itself, or as well?

> > I'm running 3.2.8 kernel with iwlwifi-5000-5.ucode and wpasupplicant 0.7.3-6 
> I would suggest testing with a newer wpa_supplicant snapshot and nl80211
> driver interface. It's likely to handle this type of networks quite a
> bit better.

Ok, it seems that the  debian unstable package, 0.7.3-6,
does support this already, it's running fine.
/sbin/wpa_supplicant -u -onl80211 -O/var/run/wpa_supplicant -f /var/log/wpa_supplicant.log

So it seems that my version already supports the new interface.

I also found
thank you, but it doesn't really explain why one would want to switch
to the nl80211 driver.

Now, this problem will likely affect a bunch of ubuntu laptops at work
(lucid or precise) and it's not very practical for me to go and give them
all git checkout code, although that can be done if it's the only resort.

Can you briefly explain how changing the control interface helps in this
Are you hopeful that new communication interface will stop telling the
driver to disconnect from 5Ghz and back to 2.4Ghz, assuming that's what's
going on?

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