wpa_supplicant and roaming

Jouni Malinen j
Mon Jul 30 09:26:47 PDT 2012

On Mon, Jul 30, 2012 at 02:02:08PM +0000, Atul Joshi wrote:
> I was looking at ap_scan parameter in wpa_supplicant.conf. The default value of ap_scan =1, Does it mean that the driver should not support roaming and should depend on the wpa_supplicant for the AP selection? Also if ap_scan = 2, this implies the driver supports roaming, does it cause any issues in firmware especially if APs support different cipher suites?

This type of division between ap_scan 1 and 2 were pretty much the rule
in the past, but this situation has changed quite a bit over the last
year or so. Nowadays, I would much rather encourage using the default
ap_scan=1 value and make sure the driver advertises its (or well,
firmware's) roaming capability. This will result in a mix of ap_scan=1
and ap_scan=2 functionality that allows scan results to be used for
network (ESS) selection and driver/firmware for BSS selection (roaming).

One example of how this is done in the ath6kl driver. With nl80211, the
driver capability is advertised with the NL80211_ATTR_ROAM_SUPPORT
attribute which can be set with the WIPHY_FLAG_SUPPORTS_FW_ROAM flag in
a cfg80211-based driver.

That said, there is usually an assumption that driver/firmware-based
roaming will use consistent cipher suite configuration. wpa_supplicant
will configure the driver with a single option.

Jouni Malinen                                            PGP id EFC895FA

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