Wireless NICs not obeying 'SSID' setting.

Sam Leffler sam at errno.com
Fri Jun 29 04:33:07 UTC 2007

Sam Leffler wrote:
> Kevin Gerry wrote:
>> I've noticed that in a recent patch that when you set a NIC with ifconfig
>> ath0 ssid "This One" that it won't always honor that and jump on the
>> strongest one.
>> Example:
>> 3 WAPs: SSIDs WAP1, WAP2, WAP3
>> I have set ath0's ssid to "WAP2" and ral0's ssid to "WAP3". They both will
>> honor the ssid setting for the first connection. However, after a few
>> hours/etc the drivers both associate with WAP1.
>> The settings to require the specific SSID are in
>> /etc/start_if.ral0/start_if.ath0. There aren't any conflicting
>> directives to
>> force it to go blank and select a random AP.
> You're probably roaming.  wlandebug roam will verify what's going on.
> You can disable roaming several ways:
> ifconfig ral0 roaming device
> should do the trick (if you set it to manual then you won't do what you
> want if your beacon is turned off).  Alternatively you can do
> ifconfig ral0 -bgscan
> as roaming won't take place w/o bg scanning.

If you are roaming you can also just fiddle with the roaming thresholds; 
   e.g. roam:rssi11g and roam:rate11g.  I haven't updated the man page 
for ifconfig for these yet; they are threshold settings that when 
crossed cause the system to consider roaming to a different ap.

The handling of ssid changed when roaming went in; it's now a "desired 
ssid".  That is, if the scan doesn't see an ap with the desired ssid 
then it'll associate to another ap if possible.  Should the ap w/ the 
desired ssid re-appear and roaming is enabled then you'll switch over to 
it.  There is also hysteresis to this algorithm so you don't just bounce 
around from one ap to another.


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