Re: Network Manager reason codes

[Sven Nielsen <post svennielsen de>]

On Fri, 11 Feb 2011 20:17:27 +0000
mike cloaked <mike cloaked gmail com> wrote:

> I totally agree but I would like to know where any misconfiguration
> has happened - all I do is boot the machine and NetworkManager shows
> the available connections - and I connect - where do I then have to
> look for misconfigured files? Or is this a set of standard

Misconfiguration in the way that NM's internal default values are not well chosen.

> different from configs in your operating system?  Are you also using
> Fedora or a different linux distribution?

Ubuntu 10.10

> Maybe I am missing something but presumably iwconfig is a temporary
> work around each time I boot the laptop - and it would seem that since
> NM would attempt a connection before I got a chance to set up a
> terminal and enter commands from the CLI then NM would already have
> done the wrong thing for me.
> 
iwconfig can change parameters after a connection is up.

 iwconfig is not in itself for workarounds. It is a tool for setting parameters of the
wlan card. NM also acts on these parameters, and might set them subotpimal. 
So, to analyse if your problem is hardware/driver/NM related, fiddling with iwconfig can give hints.  

> I presume you would need to enter something like "iwconfig wlan0 sens 10"
> and then restart NM to see if that helped - but it would mean doing
> this workaround each time I boot the machine?

Yo do not need to restart NM. iwconfig value changes take effect immediately while an interface is up.

No, according to "man iwconfig" it would mean setting it to some negative value:
Go to the location in the middle between your access points. You find this by issuing "iwlist <wlan_if> scan"
repeatedly. Monitor the "Signal level": If both APs show roughly the same level, say e.g. "-55 dBm", you have
found the middle. Now, set "sens" to some value a little lower, e.g. 

iwconfig <wlan_if> sens -60

Your card "should" then switch APs as soon as you "cross" this middle signal level.

You can automate this setting by adding, as root, a script in /etc/network/if-up.d/

Name it e.g. "set_sens" and, in the script:

#!/bin/bash                                                                                                                                     

if [ "$IFACE" = <wlan_if> ]; then
    iwconfig <wlan_if> sens -60
    # use this to check if script works:
    # iwconfig <wlan_if> txpower 3
fi

(Replace "<wlan_if>" with wour interface name). Make the script executable for all.

In theory, NM should then honour this script and set the sens value each time it brings up your
wlan interface.  The script should be triggered when disabling and enabling again wireless through NM tray
icon.

Check if the script works by changing a value you can monitor, e.g in the script set "txpower" to 3 instead
of the sens value. After completely disabling wireless an enabling it again, iwconfig should show 
"Tx-Power=3 dBm"

> Possibly once connected altering the value of the sens command may
> then help the roaming aspect if what you suggest will help my use
> case.

Yes, changing it after being connected should help.
And the above script should automate the process.

I hope the NM on Fedora honours the if-??.d scripts, too.

> You mean set up wpa_supplicant manually?  I used to do this but I
> thought that we had moved forward to a more modern era where doing
> this manually was a thing of the past!

No, if wireless-tools and wpasupplicant are installed you can put a simple config in /etc/network/interfaces:

iface wlan0 inet dhcp
	wpa-ssid YOUR_SSID
	wpa-passphrase <your_passphrase>
	...

This would be for wpa2, for WEP you would use "wireless-essid" etc. 
See /usr/share/doc/wpasupplicant/ and "man wireless" for more info.

Regards,
Sven