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Thu 23 July 2015


D-Link wireless N 150 (DWA-121) Pico USB adaptor install.

[kevin@raspberrypi ~]$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp.
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
Bus 001 Device 004: ID 2001:3308 D-Link Corp. DWA-121 802.11n Wireless N 150 Pico Adapter [Realtek RTL8188CUS]

Note: If you don't see it, make sure it is the only USB device plugged in because it takes a lot of power. Otherwise attach to a powered USB hub and you should be fine.


First create a file with the following information, but substitute in the correct ssid and psk (with quotes around them) for your network.

[kevin@raspberrypi ~]$ more /etc/wpa_supplicant/wpa_supplicant.conf

    ssid="wireless access point name in quotes"
    pairwise=CCMP TKIP
    group=CCMP TKIP
    psk="pass phrase in quotes"

Note: The ssid is case sensitive!!

Static IP Address

If you will need to change your network interface for a static IP to:

[kevin@raspberrypi ~]$ more /etc/network/interfaces
auto lo
iface lo inet loopback

# dynamic interface
#iface eth0 inet dhcp

# static interface
iface eth0 inet static

auto wlan0
iface wlan0 inet static
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

Note that the wifi interface (wlan0) points to the WPA config file from above. Also there is an example dynamic interface commented out (iface eth0 inet dhcp) to show you how to use DHCP. The lo is the loopback interface, eth0 is the wired interface, with the wlan0 being the wireless interface. Also, the lines with auto in them tell linux to automatically start those interfaces during the bootup process.

Dynamic IP Address

If you are fine with DHCP determining all your IP addresses:

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp

Finally to get the wireless up and running, use ifup to get things started.

[kevin@raspberrypi ~]$ sudo ifup wlan0
ioctl[SIOCSIWAP]: Operation not permitted
ioctl[SIOCSIWENCODEEXT]: Invalid argument
ioctl[SIOCSIWENCODEEXT]: Invalid argument

These errors don't seem to effect the wifi adaptor. You can double check all is well by using iwconfig.

[kevin@raspberrypi ~]$ iwconfig
lo        no wireless extensions.

wlan0     IEEE 802.11bgn  ESSID:"GC9J2"  Nickname:"<WIFI@REALTEK>"
          Mode:Managed  Frequency:2.437 GHz  Access Point: 00:7F:28:05:4D:D9
          Bit Rate:150 Mb/s   Sensitivity:0/0
          Retry:off   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=100/100  Signal level=76/100  Noise level=0/100
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

eth0      no wireless extensions.

Looking at the wlan0 interface, it has a 150 Mb/s data rate (802.11n), and sees a signal strength of 76/100.

[kevin@raspberrypi ~]$ ifconfig wlan0
wlan0     Link encap:Ethernet  HWaddr fc:75:16:04:96:5f
          inet addr:  Bcast:  Mask:
          RX packets:59222 errors:0 dropped:63403 overruns:0 frame:0
          TX packets:11365 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:92009000 (87.7 MiB)  TX bytes:1154992 (1.1 MiB)

Notice here a lot of dropped packets on the receive (RX).

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