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Can you explain how to understand what the 'iwconfig' command displays in Ubuntu-9.04?

Chloe Ramirez |

I'm having trouble making my wireless connection work, and I realized I don't really know how to use the tools I have, in this case, the iwconfig command in Ubuntu-9.04. Here is what I get:

***iwconfig***

-

lo no wireless extensions.
eth0 no wireless extensions.
wmaster0 no wireless extensions.
wlan0 IEEE 802.11bgn ESSID:"Network" Mode:Managed Frequency:2.412 GHz Access Point: Not-Associated Tx-Power=20 dBm Retry min limit:7 RTS thr:off Fragment thr=2352 B Power Management:off Link Quality:0 Signal level:0 Noise level:0 Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:0 Missed beacon:0
vboxnet0 no wireless extensions.
pan0 no wireless extensions.

"Network" is the name of my wireless network, btw. But what does this all mean? How can this information help me aquire a working wireless connection?

When I try associating a key using

sudo iwconfig wlan0 key s:my_key

I get the following error message:

Error for wireless request "Set Encode" (8B2A) : SET failed on device wlan0 ; Invalid argument.

I do have the right key though, so what's the problem?

4

8 Answers

wlan0 IEEE 802.11bgn ESSID:""

Means your card supports 802.11 b/g/n standards and you are currently not connected to any network (ESSID, the name identifying network is empty)

Mode:Managed

Operating mode for the device. Depending on your card, you may select one of these:

  • Ad-Hoc (network composed of only one cell and without Access Point)
  • Managed (node connects to a network composed of many Access Points, with roaming)
  • Master (the node is the synchronisation master or acts as an Access Point)
  • Repeater (the node forwards packets between other wireless nodes)
  • Secondary (the node acts as a backup master/repeater)
  • Monitor (the node is not associated with any cell and passively monitor all packets on the frequency)
  • Auto.

Frequency:2.412 GHz

Or channel - same as you see in GUI tools to manage wireless cards - you may input either frequency or channel number

Access Point: Not-Associated

Gives you exact MAC address of AP you're connecting to. If you have multiple AP's in your network and you'd like to figure out to which AP you're connected.

Tx-Power=20 dBm

This is your card's transmit power - basically the higher, the more energy your card will require.

Retry min limit:7

This option describes retry behaviour of your card.

RTS thr:off

This describes whether your card checks for clear channel every time it sends a packet. This may improve performance in some cases.

Fragment thr=2352 B

This describes maximum packet size your card will send - basically if you have a noisy environment, the smaller the packets, the less probable is that your packet would have to be retransmitted, and if it would happen, the less data would have to be transmitted. According to manual, if this value is higher than maximum packet size, the card may send several packets together.

Power Management:off

This option gives information about power management your card use. You may choose to discard some packages (ie. bcast and mcast), set your card's activity cycles and some other options.

Link Quality:0 Signal level:0 Noise level:0

If your card is connected, this is where you'd be looking for link quality:) Signal level and noise level may be given dBm or any arbitrary unit.

Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0

Some statistics about errors during receiving: nwid means that probably there's another network in your neighbourhood using the same channel as yours, invalid crypto is a number of packet you card was unable to decrypt, invalid fragmentation means there were some packets missing.

Tx excessive retries:0

This is the number of packets your card was unable to deliver.

All above is based on iwconfig manual, you may find hml version here.

If you're going to configure your card using command line tools, be sure to turn networkmanager off and use Sathya's answer. If you have your key as a text, use

sudo iwconfig wlan0 key s:your_key

instead of 

sudo iwconfig wlan0 key ABCD-1234-5678-EFG2
3

I'm surprised no one has bothered to mention this in the answers above but it sounds like you're really trying to get the wifi connection to work under linux -- not so much to understand each iwconfig parameters in all its gory details.

With this in mind it's crucially important to point out that iwconfig does not support WPA/WPA2 negotiation & authentication when connecting to a wlan network. That is to say the only wifi networks you can connect to with iwconfig are open unencrypted networks and WEP enabled networks.

Now the reason you're getting this strange error:

Error for wireless request "Set Encode" (8B2A) : SET failed on device wlan0 ; Invalid argument.

is because iwconfig is expecting a WEP-key for the key: parameter. Because of the way WEP works, this key has to meet one of these conditions:

  • ascii string that's exactly 5 characters in length
  • ascii string that's exactly 13 characters in length
  • hexidecimal string that's exactly 10 characters in length
  • hexidecimal string that's exactly 26 characters in length

Of course your key is 6 characters so this won't work and thus the error. Note that my_key technically, isn't a valid PSK either -- WPA/2 requires a minimum of 8 characters.

All this begs the question: so how do you connect to a WPA-TKIP/WPA2-AES enabled wlan? The answer is you have to use yet another program like wpa_supplicant. If you're not too crazy about the commandline method using a gui network manager like wicd manager will make this process much more seamless.

Any secure wifi network won't be using WEP since it's broken so it's important to realize iwconfig by itself can't connect to the more secure WPA/WPA2.

8

Just edit /etc/network/interfaces and write:

auto wlan0
iface wlan0 inet dhcp wpa-ssid <ssid> wpa-psk <password>

After that write and close file and use command:

dhclient wlan0
3

For people with a "Set encode" problem, try what Carlanga user wrote in this blog.

sudo gedit /etc/network/interface

Clear everything and leave only:

auto lo
iface lo inet loopback

Then, restart.

2

These are your network interfaces:

  • lo
  • eth0
  • wmaster0
  • wlan0 ( this interface is Wireless interface )
  • vboxnet0
  • pan0

The interface supports IEEE 802.11bgn.

ESSID:""
Access Point: Not-Associated

Indicates that the wireless interface is not connected to any wireless network.

To connect to a Wireless network, first type:

sudo iwlist wlan0 scan

This scans and lists all wireless networks which broadcast their ESSID. Assuming the ESSID is "Rox", then connect to the network.

sudo iwconfig wlan0 essid "Rox"

If the network requires a Key then, associate the key:

sudo iwconfig wlan0 key ABCD-1234-5678-EFG2

Finally, request for an IP:

sudo dhclient wlan0

You should be able to connect.

2

iwconfig is identical to ifconfig, although it is for wireless devices installed on your machine. It can be used to set or display parameters, and show statistics. The wireless statistics are the same as you would find in /proc/net/wireless. Your output shows you currently have 1 functioning WLAN device, wlan0.

1

Wow, for so long no has solved this problem still. If you're getting the error:

Error for wireless request "Set Encode" (8B2A) : SET failed on device wlan0 ; Invalid argument.

Instead of using "key" to include the WEP key, use "enc" instead.

iwconfig wlan0 essid "ESSID" enc "MY KEY"

.. then finish off with a

dhclient wlan0

1

Sorry dont see what you are doing with the s: try 

sudo iwconfig wlan0 essid "name"
sudo iwconfig wlan0 key "key"
sudo ifup wlan0
sudo ifdown wlan0
2

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