On Monday 14 Mar 2011 8:59:10 pm Anoop Viswanath wrote: > 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).
Thanks Anoop. Really handy. -- Fayaz Yusuf Khan B.Tech. Computer Science & Engineering (2007-2011) Model Engineering College, Kochi, Kerala, India +91-9746-830-823
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