hostap passive scanning.

Jouni Malinen jkmaline at cc.hut.fi
Fri Feb 11 00:13:10 EST 2005


On Thu, Feb 10, 2005 at 11:08:22AM -0500, Andrea G Forte wrote:

> In manual mode "host_roaming  2" we have "more" control on the scanning 
> process.
> In particular (as you know), in the driver there are two commands for 
> forcing the firmware to start the probing part of the scanning 
> (_RID_HOSTSCAN) and for forcing the Auth./Ass. part of the scanning 
> (_RID_JOINREQUEST). However, the first one is for active scanning only 
> (i.e. probes are sent to force APs to answer).

> Does the ap_scan functionality send probes on each channel (in which 
> case it is active scanning)? Or does it use passive scanning (listens 
> for beacons and records the results)?

It does not send Probe Requests.

> To be more clear, I would like to know if instead of triggering active 
> scanning (sending probes with _RID_HOSTSCAN), I can use the 
> hostap_passive_scan function in hostAP to change channel and then use 
> (or write if not already there) some other code to listen for beacons on 
> each channel and record the APs found with the signal strenght (measured 
> from the beacon). All of this while being in Managed mode.

Changing channels in managed mode is somewhat complex issue since this
is usually done only to go to the same channel with the current AP. In
other words, firmware may try to change channels based on this.

I'm still somewhat unclear on why you would like to use passive scanning
in this way. It takes much more time to scan passively. If you really
want to do it and don't care about the gaps in connectivity, you could
as well just move to Master mode and do the scanning there. For
Managed mode, it would probably be better to use firmware to take care
of the passive scanning.

-- 
Jouni Malinen                                            PGP id EFC895FA



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