~~NOTOC~~
====== Automatic Network selection ======



The following article explains how to use the linux network configuration scripts to automatically select the correct network/settings according to the location (i.e. avilable essid).

===== Procedure =====

This is the /etc/network/interfaces file :


  auto ath1
  
  iface jaist inet dhcp
       wireless-essid JAISTALL
  
  iface home inet dhcp
       wireless-essid MyPlace pre-up /sbin/wpa_supplicant_5.4 -Bw -dd -Dwext -iath1 -c/etc/fonera.conf 
       post-down killall -q wpa_supplicant_5.4
  
   
  # For temporary locations using wep
  #     iface temp inet dhcp
  #     wireless-essid TMP
  #     wireless-key1 s:password
  #     wireless-defaultkey 1
  #     wireless-keymode open
  
  
  mapping ath1
       script /mapper
       map MyPlace                   ,, home
       map JAISTALL 00:0F:23:A4:A4:00,, jaist
       map TMP                       ,, temp
  
  # Add MAC addresses after the SSID, if the wireless network does not broadcast
  # essid, at least one MAC address of one accesspoint must be defined. On
  # networks that boradcast the essid, there is no need to configure MAC
  # addresses.
  
  
  iface ath0 inet dhcp
       wireless-essid MyPlace
       pre-up /sbin/wpa_supplicant_5.4 -Bw -dd -Dwext -iath1 -c/etc/fonera.conf 
       post-down killall -q wpa_supplicant_5.4


 

The "MyPlace" is the essid that I use at home and "JAISTALL" is the essid at school. At home I use WPA (wpa_supplicant) while in JAIST its MAC based access control.

The mapper file selects the virtual interface according to which essid is available 

  #! /bin/bash
  
  ifname=$1
  
  ifconfig $ifname up
  
  function log { 
  
    time=$(date +%d%m%y-%H:%M:%S)
    echo $time   $@ >> /tmp/res
  
  }
  
    function TestMac {
    
    ifname=$1
    vifname=$2
    mac=$3
    
    
    
  if [ "$mac" != "" ]
  
  then
  
       log "Looking for MAC address $mac using $ifname"
       res=$(iwlist $1 ap | grep $mac)
       if [ "$res" != "" ]
       then
               log "MAC address found, mapping $ifname to $vifname"
               echo $vifname
       else 
               log "Not found"
       fi
  fi
  
  }
    
  while read ssid mac vifname 
  do
       log "Mapping $ifname to $vifname {$ssid}"
  
       if [ "$(iwlist $ifname scanning | grep $ssid)"  != "" ]
       then
               log "$ssid found mapping $ifname to $vifname !"
               echo $vifname
               exit
       fi
  
       # process mac addresses if they exist
  
       MAC1=$(echo $mac | cut -d"," -f1)
       MAC2=$(echo $mac | cut -d"," -f2)
       MAC3=$(echo $mac | cut -d"," -f3)
  
       TestMac $ifname $vifname $MAC1
       TestMac $ifname $vifname $MAC2
       TestMac $ifname $vifname $MAC3
  
  done




===== Usage =====

When your laptop boots, the interface ath1 will be configured according to your location. At anytime, you can run "ifup ath1" to setup your interface by hand. You can enforce some location for example by issuing "ifup ath1=jaist" in order to connect to essid JAISTALL when both essids (JAISTALL and MyPlace) are available ...





===== Note =====

If you are planning to use these files, be sure to change the following items accorsing to your own setup.

    * ath1 : the wireless interface name
    * MyPlace : The essid at your home, or location 1
    * JAISTALL : The essid of your second location
    * /sbin/wpa_supplicant_5.4 : Path to the wpa_supplicant program
    * /etc/fonera.conf : path to the configuration file for the wpa_supplicant program


{{tag>howto wireless unix}}