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original in cn Wang Xu
cn to en Wang Xu
Wang Xu is a PhD student in Beijing University of Posts and Telecommunications, China, and engages in wireless communication. He became a Linux lover since 1999 when he was a college student. Besides Linux, he also likes TeX, C/C++, Perl, etc.
WLAN (IEEE 802.11b/a/g) becomes more and more popular as WLAN devices become cheaper and more organizations provide WLAN access to their staff or to the public. Almost every new laptop computer has an embedded WLAN card and older ones may use a PCMCIA WLAN card; even desktop computers may have USB WLAN cards or even on-board WLAN cards. On the other hand, WLAN Access Points (AP) are deployed on campuses, office buildings, hotels, residences and so on. The WLAN facilitates the deployment of local networks and supports mobile/nomadic computing, which is another revolution to our working and daily life.
Thus, in the Linux world, it is also essential to support WLAN access. The rest of this article is organized as follows: let's consider how to drive the cards first; then try to access networks using authentication; and give a brief introduction of the tools for WLAN interface configuration; in the end, we will draw a conclusion.
Once you get a Wireless LAN card installed in your computer, the first step to do is to install the driver and make it work. A WLAN card implements the functions of the physical layer (PHY) and media access control sublayer (MAC) as specified in at least one of the IEEE 802.11 series of protocols, while the driver controls the card, provides a network interface identical to an ethernet interface, and provides other WLAN specific management interfaces.
There is no unified method to install drivers for the diverse number of vendors and cards. However, most of them can be driven through three methods:
Note, even if you use one of the latter two methods, you must make sure that the wireless LAN support has been set in the kernel configuration:
gnawux@APTITUDE:~$ grep CONFIG_NET_RADIO /boot/config-`uname -r` CONFIG_NET_RADIO=yIf not, you should reconfigure the kernel and enable the option "Wireless LAN (non-hamradio) Drivers and Wireless Extensions".
The drivers that are mature enough and that don't have license issues are introduced into the Linux Kernel. Therefore, the supported WLAN cards list in kernel is dependent on the version of kernel, and it is smart to check whether the new kernel has better support for your card before you install the driver.
In this section, the author will illustrate how to use the driver for WLAN cards based on the Intersil Prism chipsets (ISL38xx). The supported cards list can be found at http://prism54.org [2].
To use a Prism based card, you need the latest 2.6 kernel, and enable the "Intersil Prism GT/Duette/Indigo PCI/Cardbus" option in the Wireless LAN driver section of the kernel configuration, and re-build the kernel.
If you read the help text of the module carefully when you configure the kernel, you may find that you need to get a firmware from the prism54.org project website [2]. This is because the card does not have an EPROM to store its firmware. Therefore, it needs to download the firmware when the driver is initializing the card. The firmware can not be part of the kernel because of a license issue. After getting the firmware and putting it into "/usr/lib/hotplug/firmware/", reboot your computer, and you will find that you have an additional ethernet interface provided by the WLAN card.
Many new cards, just like other new hardware, have no GPL-compatible drivers provided by the vendors, or the drivers developed by the open source community have not become mature enough to be included in the kernel. Thus, these drivers are provided as modules, and some of them will eventually be added into future kernels when they are completed.
One of the most famous drivers is ipw2100 [3] for the Intel Pro/Wireless 2100 card, which is a part of the Intel Centrino� technology and installed in many laptop computers. In this section, the author will introduce the installation of the ipw2100 driver.
Firstly, you need to download the source package of the driver as well as the firmware from the project web site, http://ipw2100.sourceforge.net. After making sure your kernel is recent enough and built with support for modules, hotplug firmware, and wireless LAN as said above, uncompress the source package:
APTITUDE:/usr/src# tar -zxvf ipw2100-1.0.1.tgzThen go into the source directory to build and install it:
APTITUDE:/usr/src/ipw2100-1.0.1# make APTITUDE:/usr/src/ipw2100-1.0.1# make installHaving installed the modules, it indicates that you need to install the firmware:
Don't forget to copy firmware to /usr/lib/hotplug/firmware/ and have the hotplug tools in place.Just as the message says: uncompress the firmware into the hotplug directory, then the installation procedure is completed. Now you can enable the ipw2100 module by doing:
APTITUDE:/usr/src/ipw2100-1.0.1# modprobe ipw2100And you may add some parameters here for different configurations. For instance, the ifname parameter can specify the interface name:
APTITUDE:/usr/src/ipw2100-1.0.1# modprobe ipw2100 ifname=wlan0Thus the interface will be named as wlan0. For other parameters, you can read the documents in the source package of the ipw2100 driver.
Unfortunately, some cards have no drivers for Linux at all or the driver does not work for a certain reason. However, this does not mean that we cannot use it under Linux. At least, we have NDIS wrapper [1].
Most of the WLAN cards for desktop or laptop computers support Windows 2000/XP, which handles the WLAN support by a standard interface called NDIS. Therefore, the drivers for such cards usually support NDIS. Thus we can wrap such a driver and let it work under Linux as if it was Windows 2000/XP, which leads us to the ndiswrapper project.
In this section, the author will install the ndiswrapper for a Netgear 121 WLAN card as an example. Firstly, you should download the ndiswrapper from the project site, http://ndiswrapper.sourceforge.net and prepare the NDIS driver for Windows. The ndiswrapper consists of a kernel module and a set of tools. You should build and install it:
APTITUDE:/usr/src/ndiswrapper-0.11# make installThen you can load the windows driver in the wrapper
APTITUDE:/usr/src/ndiswrapper-0.11# ndiswrapper -i ../wg121/WG121V200/ndis5/netwg121.infwhere the .inf file is the NDIS driver for Windows. Having installed the NDIS driver, you may see
APTITUDE:/usr/src/ndiswrapper-0.11# ndiswrapper -l Installed ndis drivers: netwg121 driver present
Cheers! The installation procedure is completed.
If you access a WLAN in some public environment, the WLAN may require some authentication methods for security reasons. Most of the available authentication methods for WLAN are based on IEEE 802.1x (EAP) and IEEE 802.11i, and EAP based methods are currently the most popular.
There are many EAP based authentication methods, e.g. EAP-MD5, EAP-TLS, EAP-TTLS, EAP-SIM, LEAP, etc. Linux users can use xsupplicant provided by the Open1x project [4] to access a network that requires 802.1x based authentication. In this section, the author will use the LEAP protocol, which is proposed by Cisco corp., as an illustration. Note: whether the protocol can be supported is dependent on the card and the driver, i.e. even if your xsupplicant is correctly installed and configured, you may still be unable to access the network because of the card or driver not supporting it.
You should download xsupplicant from the project site, http://open1x.sourceforge.net, and install it. Then modify the configuration file, /etc/xsupplicant/xsupplicant.conf. Here is an example for LEAP.
#example of /etc/xsupplicant/xsupplicant.conf
#for LEAP protocol
network_list = all
#the list of networks to access
default_netname = default
#the default access network
first_auth_command = <BEGIN_COMMAND>dhclient %i<END_COMMAND>
#The command before authentication, which is usually used to get some info from
#the network
logfile = /var/log/xsupplicant.log
#log file
myssid #here is your network id, may be listed in the network list
{
type = wireless
ssid = <BEGIN_SSID>myssid<END_SSID>
allow_types = all
identity = <BEGIN_ID>aptitude<END_ID>
eap-leap {
username = <BEGIN_UNAME>aptitude<END_UNAME>
password = <BEGIN_PASS>passwd<END_PASS>
}#setup for leap
}
LEAP is a simple authentication method, and there are many other
settings for other methods, please refer to the examples and documents from
xsupplicant.
As you know, WLAN provides an network interface identical to ethernet, and you can use it as another ethernet interface. On the other hand, a WLAN card has much more features than a ethernet card because of the wireless media. Thus there is a set of tools to configure WLAN and obtain information about the status of it. You can find the wireless tools from http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Tools.html [5], which is contributed by Jean Tourrilhes.
The most useful tool is iwconfig, which can be used similar to ifconfig. The iwconfig command without any parameters but the interface name will print the working status of the card:
gnawux@APTITUDE:~$ /sbin/iwconfig wlan0
wlan0 unassociated ESSID:off/any Nickname:"ipw2100"
Mode:Managed Channel=0 Access Point: 00:00:00:00:00:00
Bit Rate=0 kb/s Tx-Power:off
Retry:on RTS thr:off Fragment thr:off
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
With the "mode" parameter, you can change the WLAN card working mode:
APTITUDE:/home/gnawux# iwconfig wlan0 mode 1
APTITUDE:/home/gnawux# iwconfig wlan0
wlan0 unassociated ESSID:off/any Nickname:"ipw2100"
Mode:Ad-Hoc Channel=0 Cell: 00:00:00:00:00:00
Bit Rate=0 kb/s Tx-Power:off
Retry:on RTS thr:off Fragment thr:off
Encryption key:off
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
Here we change the WLAN card into "Ad Hoc" mode. We can also change
the network name through the "essid" parameter:
APTITUDE:/home/gnawux# iwconfig wlan0 essid gnawux
APTITUDE:/home/gnawux# iwconfig wlan0
wlan0 IEEE 802.11b ESSID:"gnawux" Nickname:"ipw2100"
Mode:Ad-Hoc Frequency:2.412 GHz Cell: 02:0C:F1:0F:11:2A
Bit Rate=0 kb/s Tx-Power:off
Retry:on RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=60/100 Signal level=-83 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0
You maybe have noticed that we have now more reasonable status info than
before because we have a valid ESSID. For other parameters of iwconfig,
please read iwconfig(8).
Another powerful utility is iwlist, with which we can get the list of available resources. With the "scanning" parameter, we can obtain a list of the available access points:
gnawux@APTITUDE:~$ /sbin/iwlist wlan0 scanning
wlan0 Scan completed :
Cell 01 - Address: 00:0D:BD:6F:B4:48
ESSID:"<hidden>"
Protocol:IEEE 802.11b
Mode:Master
Channel:6
Encryption key:on
Bit Rate:11 Mb/s
Extra: Rates (Mb/s): 1 2 5.5 11
Extra: Signal: -70 dBm
Extra: Last beacon: 59ms ago
Cell 02 - Address: 86:CF:C1:34:12:06
ESSID:"gnawux"
Protocol:IEEE 802.11b
Mode:Ad-Hoc
Channel:11
Encryption key:off
Bit Rate:11 Mb/s
Extra: Rates (Mb/s): 1 2 5.5 11
Extra: Signal: -37 dBm
Extra: Last beacon: 2ms ago
</hidden>
And with the "frequency" parameter (freq), we can get the frequency list:
gnawux@APTITUDE:~$ /sbin/iwlist wlan0 freq
wlan0 14 channels in total; available frequencies :
Channel 01 : 2.412 GHz
Channel 02 : 2.417 GHz
Channel 03 : 2.422 GHz
Channel 04 : 2.427 GHz
Channel 05 : 2.432 GHz
Channel 06 : 2.437 GHz
Channel 07 : 2.442 GHz
Channel 08 : 2.447 GHz
Channel 09 : 2.452 GHz
Channel 10 : 2.457 GHz
Channel 11 : 2.462 GHz
Channel 12 : 2.467 GHz
Channel 13 : 2.472 GHz
Channel 14 : 2.484 GHz
Current Channel=1
And you can refer to iwlist(8) for other parameters.
Besides the above two, there are other utilities, e.g. iwevent, iwgetid, iwpriv, iwspy, for you to obtain the working status of your WLAN card and manage it.
The author has shown the driver installation for different WLAN cards, and illustrated how to perform authentication. Powerful configuration utilities for WLAN are also introduced in the article.
Thanks to the contribution from the open source community, we can not only access Wireless LAN under Linux, but also enjoy it!