WPA_Supplicant used with CCKM.

Jouni Malinen jkmaline at cc.hut.fi
Thu Feb 16 21:46:53 EST 2006


On Thu, Feb 16, 2006 at 05:17:49PM +0100, Renaud Roques wrote:
> > documentation.. WPA2/IEEE 802.11i adds somewhat similar functionality
> > with PMKSA caching and RSN pre-authentication. These are both supported
> > in wpa_supplicant.
> 
> In which version of wpa_supplicant is it supported ?

PMKSA caching and RSN pre-authentication are supported in pretty much
all versions of wpa_supplicant. I don't remember when they were added or
whether they were included from the beginning.

> By "classical roaming", I was meaning of reducing the time of moving from
> one AP to another. Now, when I lose connection to the AP, I'm losing
> approximately 5 seconds for searching a new AP and then one or two seconds
> for authenticating to the new one. I have two main goals : reducing these
> two times.
> One solution to reduce the time of authentication is CCKM.
> Do you have a solution to reduce the time of research ? Is there a specific
> configuration of wpa_supplicant?

Difference between CCKM and PMKSA caching is quite small. PMKSA caching
needs extra 4-way handshake, but that should not take more than 10
milliseconds when using proper implementation in both the supplicant and
authenticator. Even full EAP authentication can be done in less than 100
milliseconds.

The main time consumer for roaming is likely in scanning and AP
selection. If wpa_supplicant is used in ap_scan=2 mode and the driver
supports background scanning and has a reasonably good roaming
implementation, there should not really be than long a gap in
connectivity when roaming to a new AP (assuming that the old and new AP
are within radio range from the client at the same time). Finding a good
roaming implementation from an open source Linux driver may be a bit
difficult, though, at the moment.

-- 
Jouni Malinen                                            PGP id EFC895FA



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