Need to restart network interfaces and kill wpa_supplicant, how to fix?

Question

My workplace uses 802.11x authentication for their WiFi network, and several times per day I get booted from the network and need to do the following:

1. Disable networking
2. sudo kill -9
3. Restart networking

At this point, the machine will connect to the network just fine. I don't see any weirdness in the syslog, and am running Ubuntu 12.04 (64-bit). What could be wrong?

Answer 1

I had the same problem. It turns out that Network manager is a little overzealous in switching between access points (AP's) when more than one are present. You have two options

1. Use iwlist to find out how many AP's are there:

   root@debian:/home/nofrills# iwlist wlan0 scan
   
   Scan completed :
     Cell 01 - Address: 00:1E:58:A1:41:87
               ESSID:"iiserk_wireless"
               Mode:Managed
               Frequency:2.462 GHz (Channel 11)
               Quality:4/5  Signal level:-64 dBm  Noise level:-92 dBm
               IE: IEEE 802.11i/WPA2 Version 1
                   Group Cipher : TKIP
                   Pairwise Ciphers (2) : TKIP CCMP
                   Authentication Suites (1) : 802.1x
                  Preauthentication Supported
               Encryption key:on
               Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
                         12 Mb/s; 24 Mb/s; 36 Mb/s; 9 Mb/s; 18 Mb/s
                         48 Mb/s; 54 Mb/s
   
     Cell 02 - Address: 00:1E:58:A1:54:7B
               ESSID:"iiserk_wireless"
               #More such details
   

   Then note the Address of the cell with the highest Quality. That is the AP nearest to you. Then click on Network manager applet, select "Edit Connections" and go to the wifi network listed. There will be a text box titled "BSSID". Paste the Cell address there.

2. Otherwise, you can ditch network manager altogether and use wpa_supplicant (Network manager uses it under the hood anyway). Just create a configuration file and edit your /etc/network/interfaces this way:

   auto lo
   iface lo inet loopback
   
   auto wlan0
   iface wlan0 inet dhcp
       pre-up wpa_supplicant -B -Dwext -i wlan0 -c/etc/wpa_supplicant.conf
       post-down killall -q wpa_supplicant 
   

Option 1 is not very useful unless you spend most of your time at workplace in roughly the same location. Option 2 is what I am using now, and it works pretty well. But wifi does not get automatically reconnected after suspend/resume, so you need to run /etc/init.d/networking/restart manually.

If you like doing things neatly, as an alternative to the generic killall command, you can use the WPA specific tool wpa_client:

wpa_cli -i wlan0 terminate

Answer 2

sudo service network-manager stop

It will stop NetworkManager