Debian Linux Configure Wireless Networking With WPA2

I've Atheros AR5001 wifi a/b/g card detected and supported natively under Linux. How do I configure my wireless card with WPA2 networking using /etc/network/interfaces file?

Wi-Fi Protected Access II (WPA2 i.e. IEEE 802.11i) is security protocols for wireless communication. It introduces CCMP, a new AES-based encryption mode with strong security in mind. Under Debian Linux you need to install wpasupplicant to support for WPA and WPA2 networks. Open a command-line terminal (select Applications > Accessories > Terminal), and then type the following commands as root user:

Step #1: Install wpasupplicant

To install wpasupplicant simply type the following command as root user:
# apt-get install wireless-tools
OR
# apt-get install wpasupplicant

Step #2: Verify WiFi / Wireless Card Is Detected

Use the lspci command to verify that card is detected:
# lspci
# lspci | grep -i wlan
# lspci | grep -i wireless
# lspci | grep -i wifi
# lspci -nn | grep Network
Sample outputs:

0c:00.0 Network controller: Intel Corporation Ultimate N WiFi Link 5300

This page explains the lspci command to find out Wireless driver chipset information under Linux. Or you can go to Linux wireless LAN support page and make sure your card is listed as supported device under Linux. You can also see your wireless interface name using the following command:
# ifconfig -a
OR
# dmesg | grep -i wlan
# dmesg | grep -i wireless

Step #3: Configure WPA2

Edit /etc/network/interfaces file, enter:
# vi /etc/network/interfaces
Setup wlan0 with the SSID and PSK as follows:

 
auto wlan0
iface wlan0 inet dhcp
    wpa-ssid YOUR-SSID-HERE
    wpa-psk YOUR-PASSWORD-HERE
 

Make sure you use strong pass-phrase. Save and close the file. You can now connect to the interface, enter:
# ifup wlan0
# ifconfig wlan0
# ping router-ip-here
# ping google.com
OR you can restart the networking service using any one of the following method:
# /etc/init.d/networking restart
OR
# service networking restart

Get Info About Your Network

To see more info about wifi, enter:
# iwconfig wlan0

Scan Your Wireless Network

Type the following command:
# iwlist wlan0 scan

Sample /etc/network/interface Config File

 
# The loopback network interface
auto lo
iface lo inet loopback
 
# The primary network interface
auto eth0
iface eth0 inet static
        address 192.168.1.5
        netmask 255.255.255.0
        network 192.168.1.0
        gateway 192.168.1.1
 
# The wireless network interface with dhcp
auto wlan0
iface wlan0 inet dhcp
    wpa-ssid nixcraft
    wpa-key-mgmt WPA-PSK
    wpa-group TKIP CCMP
    wpa-psk YOYR-PASSWORD-HERE
 

Troubleshooting wpa_supplicant

See wpa_supplicant log file /var/log/wpa_supplicant.*.log using the tail, more, or grep command:
# tail -f /var/log/wpa_supplicant.wlan0.log
# grep 'something' /var/log/wpa_supplicant.wlan0.log

A Note About GUI Configuration Tool

You can use NetworkManager - a graphical interfaces for GNOME and KDE. If you are using NetworkManager, avoid using Debian's /etc/network/interfaces file. See this page for more information about Gnome / KDE wireless network config tool.

Recommended readings:

Anytime you need assistance with Linux wifi configuration option, turn to the following man page first. It will give you detailed information, parameters and switches for wifi configurations. For example, man 5 interfaces opens the man page for the interfaces network configuration file:
$ man 5 interfaces
$ man 8 wpa_supplicant
$ man 8 iwconfig
$ man 8 iwlist