When several APs run with same SSID

andrixnet · 04-01-2016, 07:41 AM

I am using a linux (slackware) box in an environment with several APs, all with same SSID and same auth. A couple of them are actually wireless repeaters.
An android phone can dynamically disconnect from an AP with very poor signal if it senses and AP of the same SSID with stronger signal (this can take up to a minute).

I have configured my linux box with rc.wireless.conf and wpa_supplicant.conf (WPA2 personal, PSK) for a stable config in this network.

How can I configure it to connect to the AP with the best signal? Apparently my box prefers only one AP, regardless the much stronger signal of another, nearby. Of course, forcing the MAC of an AP would not be preferred.

How can I reproduce the behaviour of Android phones to prefer best signal and switch AP if (significantly) better signal AP available?

I am specifically asking about rc.wireless configuration, not NetworkManager, here.

Thank you.

Paulo2 · 04-01-2016, 08:50 AM

If this doesn't exist already, you could get signal levels with iwlist in a cron job and choose the best signal.

andrixnet · 04-01-2016, 08:57 AM

My main focus is to have the network up and running at startup using rc.inet1 and rc.wireless because this ensures I have network (and I need it) before some daemons start up later.

Having NetworkManager configure the network I get connectivity about 30 sec. after the login prompt (and of course after all services have already started, but some missed a data initialization).

So the primary concern is how to connect to the best signal AP with that SSID at startup.
Second concern is switching APs later, based on signal strength.

Thank you.

Paulo2 · 04-01-2016, 11:18 AM

I'm a NetworkManager user so I don't know how to use this

Code:

iwlist_out=$(iwlist wlan0 scan);for i in $(seq $(grep -c -F Cell <<<"$iwlist_out"));do sed -nr "/Cell $(printf '%02d' $i)/,/ESSID/ { /Address/ {s/.*: (.*)/\1/;h}; /Quality/ {s/.*=([0-9]+)\/.*/\1/;x;H}; /ESSID/ {s/.*ESSID:(.*)/\1/;H;g;s/\n/\t/g;p};}" <<<"$iwlist_out";done|sort -r
70	xx:xx:xx:xx:xx:xx	"foo"
25	xx:xx:xx:xx:xx:xx	"bar"
20	xx:xx:xx:xx:xx:xx	"blah"

The output is the quality, mac and SSID.
The fist line is the AP with best signal,
you can cut that line to get SSID or mac.

dabreese00 · 04-01-2016, 02:26 PM

My brief research points to the wpa_supplicant module "bgscan" which sounds relevant. Based on what I see in /usr/doc/wpa_supplicant-[version]/wpa_supplicant.conf.sample, it might be sufficient to add

Code:

bgscan="simple:30:-45:300"

to your wpa_supplicant.conf, playing with those numbers if necessary. You can look over the documentation. Hope this helps.

Quote:

If this doesn't exist already, you could get signal levels with iwlist in a cron job and choose the best signal.

For the record, you can get signal strength readings using wpa_cli, a direct interface to wpa_supplicant, instead of iwlist (a lower-level utility which may not be 100% on the same page as wpa_supplicant). You can trigger a scan with

Code:

wpa_cli scan

and print the results with

Code:

wpa_cli scan_results

(which you can process as desired using cut, awk, or whatever if you end up having to go the cron job route).

genss · 04-01-2016, 05:09 PM

add

Code:

bssid: whateveritis

to wpa_supplicant.conf
(bssid is the mac address of the ap)

you can get the bssid from iwlist, as suggested, or

Code:

iw dev wlan0 scan