How to handle multiple SSIDs with the same BSS

Jouni Malinen j
Tue Dec 29 12:27:53 PST 2009

On Sun, Dec 27, 2009 at 05:44:38PM -0800, Marcel Holtmann wrote:

> I noticed the aging of the BSS and I do like that feature. How do you
> determinate when a BSS is too old and should be removed?

Currently, this is very simple: check every WPA_BSS_EXPIRATION_PERIOD
(10 sec by default) whether there are entries that are over
WPA_BSS_EXPIRATION_AGE (180 seconds) old and expire them if they are ot
in use (BSS entry age is the time from the last update in it, e.g.,
based on scan results). The other rule for expiring entries is based on
new scan results: expire an entry if it has not been seen in last
WPA_BSS_EXPIRATION_SCAN_COUNT (2). The latter one will eventually be
improved to handle partial scans (i.e., only some channels/SSIDs being
scanned; those should only expire matching BSS entries). In addition,
there is a maximum limit on the BSS entries (200) and new BSS entries
added above that will end up getting the oldest entry getting removed.

These values will likely end up being configurable at some point and I
have also considered providing options for controlling the BSS list
updating "mode". For example, wpa_supplicant could be requested to keep
the BSS table more frequently up-to-date for all BSSes or for specific
ESSes. This could have some connections with the bgscan mechanism. In
addition, this could get more input from things like Microsoft Wireless
Provisioning Services (multi-SSID/hidden SSID) and IEEE 802.11k neighbor
reports, etc.

Jouni Malinen                                            PGP id EFC895FA

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