wpa_supplicant.: Simulating handoff between wifi's access points.

Jouni Malinen j
Fri Dec 21 15:13:56 PST 2012

On Fri, Dec 21, 2012 at 05:14:06PM -0300, Carlos Patricio Amigo Haering wrote:
> I read in other mail from this mail-list that the roam is a developer 
> command and i need to know some low-level details to be able to use it 
> in practice. I would like to know what details are these.

One detail is that you are responsible for making sure the driver is
ready for the following authentication/association command. In practice
with cfg80211, you will need to make sure the target AP is in the scan
results. The easiest way to do this is to run a single channel scan on
the target AP's frequency (e.g., "sudo iw wlan0 scan freq 2462") just
before issuing the roam command to wpa_supplicant.

> When i use the roam, the cli shows me a error about the request to the 
> driver and doesn't change of AP and reconnect again to the current one. 

That's most likely because cfg80211 did not have a valid BSS table entry
(i.e., it had expired the previously found entry from last scan
results). That iw command to scan the channel should address this.

> By otherhand i don't know what driver is using the supplicant. wext or 
> nl80211?. How can i see that? (my network controller: Intel Corporation 
> PRO/Wireless 4945ABG)

It depends on how wpa_supplicant is started (command line or dynamic
command to add the interface) since both interfaces are likely to be
available. Anyway, for this particular case you can easily see it from
the debug entries:

> <3>SME: Trying to authenticate with 20:aa:4b:48:7e:ca (SSID='OF' 

If you see the "SME:" prefix, you are using nl80211.

Jouni Malinen                                            PGP id EFC895FA

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