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Setting up wireless with wpa2 on linux
Posted on 11-08-2007 06:23:00 UTC | Updated on 05-30-2016 22:50:53 UTC
Section: /software/wpa_supplicant/ | Permanent Link

This an example of connecting a linux laptop to an access point that uses WPA2. The example below will use an Dell Inspiron 9300 laptop running Kubuntu 7.10. The laptop uses a built in Intel PRO/Wireless 2200BG (Centrino) Network Connection mini PCI adapter. Kubuntu had the wireless card working on install (wireless driver is called ipw2200) but no setup for WPA2 that I could find.

The access point I'm going to connect to is a Linksys WRT54GL. It is running dd-wrt firmware version 23 sp2. The access point security is set to "wpa2 pre-shared key mixed" with the WPA algorithm set to "AES". The SSID will be set to "wpatest" for this example.

Before continuing any further, turn off an network manager services like "NetworkManager" which will mess with manual network setup like we are going to be doing. A "sudo service NetworkManager stop" should kill it.

The program we will need to connect to the access point is called wpa_supplicant. Supplicant is the IEEE 802.1X/WPA component that is used in the client machines. It implements key negotiation with a WPA Authenticator and it controls the roaming and IEEE 802.11 authentication/association of the wlan driver. Wpa_supplicant only supports certain drivers so if your having problems with this check the wpa_supplicant page (google it) to make sure your driver works with it. Kubuntu 7.10 comes with wpa_supplicant and other wireless tools installed.

First we need to generate a WPA PSK from an passphrase for a SSID so we can try to protect the network. We do this with the wpa_passphrase program using the "wpatest" SSID name I noted above with nice long passphrase. Your pass phrase should have some numbers and special characters in it if you can.

wpa_passphrase wpatest thisisanicelongpassphraseitisniceandlongforareason

This will output a long block of characters that your going to need to put in the /etc/wpa_supplicant.conf file. Keep it handy. Now open the file /etc/wpa_supplicant/wpa_supplicant.conf in your favorite editor. Remember to sudo when opening the file. Now paste the code below into it.

ctrl_interface=/var/run/wpa_supplicant
#ap_scan=2
# commented out lines are optional
network={
  ssid="wpatest"
  scan_ssid=1
  key_mgmt=WPA-PSK
  psk=""
  #proto=WPA RSN
  #pairwise=CCMP TKIP
  #group=CCMP TKIP
}

In the above config you will see the field "ssid=". Put your ssid for your network in there. Mine is "wpatest" above. Next, where you see the line "psk=" after the = sign you have to put the output from the wpa_passphrase we generated above. It would look something like

psk=a6e6af3e3d77b4c7dd6a3c292ecde36839a1f2d921"

Save that file and exit your editor. Now we need to setup the wireless interface. Use the comand "dmesg" to check for your wireless cards inteface. Look for eth0, eth1, wlan0, or something like that in the output. Your wired connections might look like this also so make sure it's your wireless interface. You could also try the command "ifconfig" to see if you see your wireless interface there. Kubuntu is pretty good about finding the wireless card. Once you know what it is lets bring it up. Mine is eth1 so the command would be the following.

sudo ifconfig eth1 up

Now we can scan for networks. This is good if you want to see information about the networks in the area. You might already know your access points info but if you don't just scan.

sudo iwlist scan

It will give the list of access points, Ad-Hoc cells in range, channels, and a lot more info. My access point was listed and showed it's name "wpatest" on channel 7. So lets configure the wireless interface for that.

sudo iwconfig eth1 essid "wpatest" channel 7

Now we need to start wpa_supplicant. You might need to modify command line switches -i and -D to work with your own setup. -D is the driver to use. My Intel card can use the wext driver which is the Linux wireless extensions (generic). Try that one first. If it does not work look at the man page for wpa_supplicant for other driver types like the more modern nl80211. Also, -i is the interface for your wireless card. Mine is eth1. Yours will be what you found in the earlier step. The line we need to run is the following.

sudo wpa_supplicant -B -Dnl80211 -ieth1 -c/etc/wpa_supplicant/wpa_supplicant.conf

If wpa_supplicant started successfully then you can make your dhcp request over the network to get an ip address with dhclient. I use eth1 because again it's my wireless cards interface. Specifying hostname to the DHCP client daemon may help to find the MAC address of a connecting laptop in DHCP logs on the server, in case there’s filtering for MAC addresses.

# simple example
sudo dhclient eth1

# dhcp hostname example using busybox and udhcpc
busybox udhcpc -x hostname iamhere -i eth1

After this you should have an ip and be on the network. Below is the shell script I use to start my wireless interface. If you know the settings of your access point just change to fit your needs.

#!/bin/sh
sudo pkill wpa_supplicant
sudo ifconfig eth1 down
sudo ifconfig eth1 up
# for iwconfig put in "channel 7" if you need to select a specific channel, try without it first
sudo iwconfig eth1 essid "wpatest" 
sudo wpa_supplicant -B -Dnl80211 -ieth1 -c/etc/wpa_supplicant/wpa_supplicant.conf
sudo dhclient eth1

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