Configuring WPA/WPA2 for WiFi access on Linux Clients - Part 1

Configuring a Linux WiFi client is not always as easy as with Windows or MAC OS X. In this first post I will show you how to configure your Linux client to associate with an access point. For this example, I use Ubuntu version 8.x. This procedure may vary from one Linux variant to another. The SSID I want to connect to is APN and my WiFi interface is wlan1. Here are the steps for WPA/WPA2 PSK (commands are in boldface):


1. Generate your WPA/WPA2 passphrase

wpa_passphrase APN

# reading passphrase from stdin

yoursecretkey

network={
        ssid="APN"
        #psk="yoursecretkey"
        psk=9ae7a5f631ecc688db8dcc6bbf317b4a551b39e9ee9c20effb5393e342bd954b
}


2. Copy your wpa_passphrase output to /etc/wpa_supplicant/wpa_supplicant.conf
From the above step, it starts with "Network={" and ends with a closing curly brace "}". You may want delete the comment "#psk=yoursecretkey"


3. Enable your wireless interface

ifconfig wlan1 up


4. Scan for existing WLANs or SSIDs

iwlist wlan1 scanning | grep -i essid

                    ESSID:"BELL078"
                    ESSID:"APN"
                    ESSID:"2mix"

You now have a confirmation your target SSID APN is detected.

5. Configure your wireless interface for your specific SSID

iwconfig wlan1 essid APN


6. Start WPA/WPA2 authentication

wpa_supplicant -iwlan1 -c /etc/wpa_supplicant/wpa_supplicant.conf

ioctl[SIOCGIWSCAN]: Resource temporarily unavailable
CTRL-EVENT-SCAN-RESULTS
Trying to associate with 00:25:4b:0a:a3:f5 (SSID='APNSmallBang' freq=2437 MHz)
CTRL-EVENT-SCAN-RESULTS
Associated with 00:25:4b:0a:a3:f5
WPA: Key negotiation completed with 00:25:4b:0a:a3:f5 [PTK=CCMP GTK=CCMP]
CTRL-EVENT-CONNECTED - Connection to 00:25:4b:0a:a3:f5 completed (auth) [id=0 id_str=]


7. Assign IP address via DHCP
Open a new shell to type the following command:

dhclient wlan1

Internet Systems Consortium DHCP Client V3.1.1
Copyright 2004-2008 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/sw/dhcp/

Listening on LPF/wlan1/00:c0:ca:2f:94:0d
Sending on   LPF/wlan1/00:c0:ca:2f:94:0d
Sending on   Socket/fallback
DHCPDISCOVER on wlan1 to 255.255.255.255 port 67 interval 3
DHCPOFFER of 172.16.22.5 from 172.16.22.1
DHCPREQUEST of 172.16.22.5 on wlan1 to 255.255.255.255 port 67
DHCPACK of 172.16.22.5 from 172.16.22.1
bound to 172.16.22.5 -- renewal in 33064 seconds.


8. Check if IP address assigned correctly

ifconfig wlan1

wlan1     Link encap:Ethernet  HWaddr 00:c0:ca:2f:94:0d
          inet addr:172.16.22.5  Bcast:172.16.22.255  Mask:255.255.255.0
          inet6 addr: fe80::2c0:caff:fe2f:940d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7 errors:0 dropped:0 overruns:0 frame:0
          TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1092 (1.0 KB)  TX bytes:1580 (1.5 KB)


>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>>>>>>At this point, you should be connected to your AP<<<<<<
>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


In a next post, I will show you how to automate these commands.

Comments

[KeithRParsons]

Steve,

I always knew there really was a lot going on in the background when I just 'clicked' to join a wireless network. This was good to remind me of all the real things that have to happen in the background.

Also reminded me of why I don't do Linux any more... that is just ridiculous.

Looking forward to the easy version next.

[Steve Williams]

Hi Keith,

Thanks for commenting. Lots of stuff in Linux is not easy. And there are so many distributions, take a look at DistroWatch http://distrowatch.com/. In comparison with MAC OS X by Apple and a few variants of Windows by Microsoft, it is difficult for Linux to be just "Linux". My favorite distro is Ubuntu, which I have been running for 5 years, mainly for security pentests and its excellent syslog-ng service. I am a *nix user since 1992... So it's part of my DNA so to speak.

In all my consulting career, I never came across an enterprise who uses Linux as client platform. I've seen many running Linux as a server platform. The majority of companies use Windows and some will use MACs. To me Linux is more a tool in my arsenal. I like to use the best of both worlds of Linux and Windows. This is why most of my PCs dual boot Win and Lin and sometimes triple boot. Besides, I run VMs both in Win and Lin. Whenever I do lab work and my PC booted in Linux, it's quicker for me to establish a WLAN connection using the directives from my post than rebooting in Windows and click the WLAN tray icon.

Fun fact is that ever since I started in the WiFi business, I noticed that all interesting WiFi commercial products only run in Windows, nothing is available in Linux (idem for MAC OS X). I am referring to AirMagnet and Cisco products. I need these products to do my job, so I need to stay more and more in Windows.

In my next post I will unveil how Ubuntu 9.10 equates Windows as far as establishing a WLAN connection.

[Mehdi]

Hey Steve
If you want an easy linux client, check Linux Mint. I even installed it on my parents laptop and they don't miss windows. Enuff said :)
http://www.linuxmint.com/

[Steve Williams]

Hi Mehdi,

Thanks for sharing. I never tried Linux Mint before, but I am glad to find out another Linux distribution bundles an easy WiFi client. Ubuntu 9.10 does this as well (plse see part 2 of my post).

However, if you *have to* use a Linux distro that does not offer a Mom & Pop WiFi client, you can rely on the command line, as described herein.