More people than ever are using wireless networks as their primary
networking medium. Great programs are available under X11 that give users a
graphical interface to their wireless cards. Both GNOME and KDE include
network management utilities, and a desktop-environment-agnostic utility
called wicd also offers great functionality. But, what if you aren't running
X11 and want to manage your wireless card? I don't cover how to install and
activate your card here (for that, take a look at projects like madwifi or
ndiswrapper). I assume your card is installed and configured properly, and
that it is called wlan0. Most of the utilities mentioned below need to talk
directly to your wireless card (or at least the card driver), so they need
to be run with root privileges (just remember to use sudo).
The first step is to see what wireless networks are available in your area.
A utility called iwlist provides all sorts of information about your
wireless environment. To scan your environment for available networks, do
the following:
sudo iwlist wlan0 scan
You'll see output resembling:
Cell 01 - Address: 00:11:22:33:44:55
ESSID:"network-essid"
Mode:Master
Channel:11
Frequency:2.462 GHz (Channel 11)
Quality=100/100 Signal level:-47dBm Noise level=-100dBm
Encryption key:off
.
.
.
The details (address and essid) have been changed to protect the guilty.
Also, the ... represents extra output that may or may not be available,
depending on your hardware. You will get a separate cell entry for each
access point within your wireless card's range. For each access point, you
can find the hardware address, the essid and the channel on which it's
operating. Also, you can learn in what mode the access point is operating
(whether master or ad hoc). Usually, you will be most interested in the
essid and what encryption is being used.
Once you know what's available in your immediate environment, configure your
wireless card to use one of these access points using the iwconfig utility
to set the parameters for your wireless card. First, set the essid, which
identifies the network access point you want:
sudo iwconfig wlan0 essid network-essid
Depending on your card and its driver, you may have the option to set the
essid to the special value “any”. In this case, your card will pick the
first available access point. This is called promiscuous mode.
You also may need to set the mode to be used by your wireless card. This
depends on your network topology. You may have a central access point to
which all of the other devices connect, or you may have an ad hoc wireless
network, where all of the devices communicate as peers. You may want to have
your computer act as an access point. If so, you can set the mode to master
using iwconfig. Or, you simply may want to sniff what's happening around
you. You can do so by setting the mode to monitor and passively monitor all
packets on the frequency to which your card is set. You can set the
frequency, or channel, by running:
sudo iwconfig wlan0 freq 2.422G
Or by running:
sudo iwconfig wlan0 channel 3
You can set other parameters, but you should consider doing so only if you
have a really good reason. One option is the sensitivity threshold, which
defines how sensitive the card is to noise and signal strength, and you can
set the behavior of the retry mechanism for the wireless card. You may need
to play with this in very noisy environments. Set the maximum number of
retries with:
sudo iwconfig wlan0 retry 16
Or, set the maximum lifetime to keep retrying to 300 milliseconds with:
sudo iwconfig wlan0 retry lifetime 300m
In a very noisy environment, you also may need to play with packet
fragmentation. If entire packets can't make it from point to point without
corruption, your wireless card may have to break down packets into smaller
chunks to avoid this. You can tell the card what to use as a maximum
fragment size with:
sudo iwconfig wlan0 frag 512
This value can be anything less than the size of a packet. Some cards may
not apply these settings changes immediately. In that case, run this command
to flush all pending changes to the card and apply them:
sudo iwconfig wlan0 commit
Two other useful commands are iwspy and iwpriv. If your card supports it,
you can collect wireless statistics by using:
sudo iwspy wlan0
The second command gives you access to optional parameters for your
particular card. iwconfig is used for the generic options available. If you
run it without any parameters (sudo iwpriv wlan0), it lists all available
options for the card. If no extra options exist, you will see output like
this:
wlan0 no private ioctls
To set one of these private options, run:
sudo iwpriv wlan0 private-command [private parameters]
Now that your card is configured and connected to the wireless network, you
need to configure your networking options to use it. If you are using DHCP
on the network, you simply can run dhclient to query the DHCP server and get
your IP address and other network settings. If you want to set these options
manually, use the ifconfig command (see the man page for more information).
--
Follow me on twitter : www.twitter.com/anoovis
_______________________________________________
Indian Libre User Group Cochin Mailing List
http://www.ilug-cochin.org/mailing-list/
http://mail.ilug-cochin.org/mailman/listinfo/mailinglist_ilug-cochin.org
#[email protected]
