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USB Wi-Fi adapters under Linux

By Keith Winston on January 21, 2005 (8:00:00 AM)

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I needed to connect my new desktop PC wirelessly from my second floor office to my first floor network. As I started researching the options for wireless USB adapters, I realized I might have some work ahead of me. Wireless USB in Linux is still in the early stages of development. But a little searching and some trial and error led to a successful connection.

While I did not expect the configuration to be easy, I did not expect it to be especially difficult either. To be fair, a lot of the complexities have nothing to do with the USB drivers, but are more related to the device naming and mapping changes that occurred in the upgrade from the 2.4 to the 2.6 kernel.

To better handle dynamic, hotplug devices on USB and FireWire, changes were made in the 2.6 kernel to provide persistent device names. The kernel now handles device management via two subsystems called sysfs and udev. If you run a 2.6 kernel, you may notice a new virtual directory called /sys in the root of your system. The /sys directory works like /proc in that it maps directly to part of system memory. While /proc tracks kernel parameters and state, /sys tracks device names known to the system. The device names in /sys are persistent because they are based on unique hardware and bus identifiers. This allows the kernel to always assign the same name to a dynamic device, something that was not possible in the 2.4 kernel.

In the 2.4 kernel the order you plug in USB devices can affect the name that gets assigned to it. The name of a device is neither unique nor guaranteed. The sysfs subsystem in the 2.6 kernel tries to solve that problem by naming devices using a unique identifier. The result is something not very useful to humans, as the device name for my wireless USB adapter turned out to be /sys/devices/pci0000:00/0000:00:02.1/usb3/3-1/3-1:1.0. That name is not very handy to deal with, so the udev subsystem provides a mapping between the /sys device name and the more familiar device names like /dev/wlan0.

Configuration

My initial research on wireless USB adapters landed me at the hardware compatibility list maintained by Absolute Value Systems, the company that maintains the linux-wlan project and provides drivers for several wireless USB and PCMCIA chipsets. After scanning the compatibility list, I decided to get the Linksys WUSB12 802.11b adapter. It was inexpensive and seemed to be supported.

My primary desktop runs SUSE Professional 9.1 using the 2.6.5 kernel. I plugged the new wireless adapter into an open USB port and fired up the SUSE administration tool, YaST, to see if it had been recognized. No dice. I ran an lsmod command to see if the kernel had recognized it, and was pleased to see the prism2_usb kernel module loaded. I made an attempt to configure the wireless USB card in YaST anyway, and YaST dutifully created a configuration file for it, but I was no closer to getting it to work. It was time to look at the wireless USB configuration itself.

The default location for configuration files is in /etc/wlan/ and the main file is wlan.conf. Wlan.conf is a shell script, and the only thing it does is set some environment variables.

There are only three settings in wlan.conf to check:

WLAN_DEVICES="wlan0"
SSID_wlan0="stayoutofmynet"
ENABLE_wlan0="y"

The SSID_wlan0 setting is the network identifier for the wireless network. The system looks for a network-specific configuration file based on the SSID_wlan0 setting. In this example, it looks for a file called /etc/wlan/wlancfg-stayoutofmynet for additional settings. If it does not find the network-specific file, it reads the /etc/wlan/wlancfg-DEFAULT file. The wlancfg-stayoutofmynet file contains mostly WEP encryption settings, including which key to use and the key itself.

Another important file in the process is /etc/wlan/shared, a shell script that contains the functions to enable, start, and stop the network interface. There is no need to change the /etc/wlan/shared file; it is called by other scripts to do the dirty work.

In theory, when the adapter is plugged into a USB port, the hotplug system fires an event that loads the kernel modules, then the udev and sysfs subsystems assign a name to the device and interface. When the interface is registered, more hotplug events are triggered to read the configuration files. There is a lot of new code in play here, including the SUSE shell scripts that glue everything together. After much anguish and gnashing of teeth, I could not get it to work using YaST and the default SUSE configuration. Maybe it would have worked if I had turned off encryption on the access point, but I was not going to run a wireless network and be undefended.

Manual labor

The configuration program for wireless USB cards is called wlanctl-ng. The configuration scripts that come with the linux-wlan package call wlanctl-ng with various non-intuitive parameters. Going back to Google, I found a few pages that showed manually constructed working configurations. I eventually distilled a script that has been working well for me:

#! /bin/sh
#
# Wireless USB setup
#

# Step 1 - enable wireless USB for wlan0
wlanctl-ng wlan0 lnxreq_ifstate ifstate=enable

# Step 2 - set SSID for your network
wlanctl-ng wlan0 lnxreq_autojoin ssid=stayoutofmynet authtype=opensystem

# Step 3 - set WEP attributes
wlanctl-ng wlan0 lnxreq_hostwep encrypt=true decrypt=true
wlanctl-ng wlan0 dot11req_mibset mibattribute=dot11PrivacyInvoked=true

# Step 4 - set WEP key
wlanctl-ng wlan0 dot11req_mibset mibattribute=dot11WEPDefaultKeyID=3
wlanctl-ng wlan0 dot11req_mibset mibattribute=dot11WEPDefaultKey3=12:34:56:78:9A

# Step 5 - set IP configuration
ifconfig wlan0 192.168.1.100 netmask 255.255.255.0 broadcast 192.168.1.255
route add default gw 192.168.1.11

I have used this script on both SUSE 9.1 and SimplyMEPIS 2004.06 and found it to work well for both. It should work on any 2.6 kernel-based distribution with the wlan-ng package installed, but you'll need to customize it for your own system:

  • Step 2 needs to be modified to match the SSID of your wireless network.
  • Step 4 needs to be modified to match your encryption key ID and key. This setting is zero-based, so the first key is KeyID=0. I was using key 4, and thus KeyID=3 in my example. On the following line, the mibattribute=dot11WEPDefaultKey3 value changes depending on which key you are using. For example, if you are using KeyID=0, then the following line would use mibattribute=dot11WEPDefaultKey0=12:34:56:78:9A. To complicate things further, the encryption key value can be extended. My example uses low-grade encryption. If you are using 128-bit encryption, extend the length of the key value.
  • Step 5 needs to be modified for the right IP address and gateway.
  • DISCLAIMER: You are free to use this script, hack it, copy it, sell it, digest it, and pass it through your body. However, it comes with zero technical support.

    I changed my boot configuration to call this script at the very end of the boot process after all the other services are up.

    The Linuxant option

    While researching, I ran across Linuxant's DriverLoader product, which allows you to use the Windows binary drivers that ship with many wireless cards in Linux. It is not free software, but has a low cost and can be used for a free 30-day trial.

    The Linuxant Web site provides binary packages for a number of Linux distributions. It also has the source available if you want to compile it to work with your custom kernel. I have not tested DriverLoader, but I have read testimonials indicating that it works well for supported hardware. NewsForge covered it recently.

    Filling the ether with bits

    After several months of continuous use, I am pleased to report the Linksys WUSB12 adapter is holding up well. It does not overheat and the throughput matches my laptop's old PCMCIA card.

    A few years ago, wireless USB was leading edge technology. I still consider it leading edge in the Linux world, but with a little elbow grease, your Linux systems can fill the ether with bits.

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    Comments

    on USB Wi-Fi adapters under Linux

    Note: Comments are owned by the poster. We are not responsible for their content.

    Hint

    Posted by: Anonymous Coward on January 22, 2005 03:52 AM
    I used "iwconfig" to set the wireless parameters for wlan0 when I used a pci Realtek adapter, using the windows sys driver with the module ndiswrapper module. Some directions on how to use it I believe were there on the directions on how to use ndiswrapper on SuSE's KB.

    #

    Wireless USB or Wireless Bridge?

    Posted by: Anonymous Coward on January 22, 2005 04:31 AM
    The reason you are having a hard time with this is the approach is wrong.

    Instead of playing with wireless USB contraptions and impossible configuration setups go get a 'Wireless Bridge' configuer it and then connect it to your system by standart eathernet cable via the RJ45 port. Mush less problamatic and much moer portable.

    #

    That's how I do it

    Posted by: Anonymous Coward on January 22, 2005 08:25 PM
    And I have no regrets whatsoever.

    #

    Re:Wireless USB or Wireless Bridge?

    Posted by: Anonymous Coward on January 23, 2005 01:40 AM
    with wireless usb bridge, you need a separate ac/dc adaptor, a pain in the carrying bag.

    #

    Re:Wireless USB or Wireless Bridge?

    Posted by: Anonymous Coward on January 24, 2005 12:51 PM
    The Asus WL330G comes with a usb power plug so you don't need to carry an adaptor. It's a WAP or a bridge depending on which way you flick the switch.

    #

    ndiswrapper

    Posted by: Anonymous Coward on January 22, 2005 05:02 AM
    Add note, I was using SuSE 9.1, upgraded to 9.2 and the wireless still works. Using ndiswrapper is just like using the mentioned software but is GPL licensed, or at least it should be because it comes bundled with SuSE.

    #

    Re:ndiswrapper

    Posted by: hosh on January 22, 2005 05:43 AM
    Yes, ndiswrapper is GPL'ed. I used it with some Belkin 54G cards I had. It worked pretty good after I figured out how to load the driver without hanging the kernel. Because there was no signal strength support (implemented in a non-standard way in Windoze) and other issues I returned them to the store.

    #

    Re: Hardware List.

    Posted by: Anonymous Coward on January 22, 2005 06:09 AM
    That particular hardware list is outdated. The currently shipping Linksys WPC54G does not have the Broadcom Chipset, it has the RaLink RT2500.

    Unfortunately, as the wireless manufacturers do not always announce when chipsets have been changed, following one of the hardware compatibility lists found on various websites amounts to a crap-shoot if you are expecting compatibility with Linux.

    #

    wlan included in your distribution

    Posted by: Anonymous Coward on January 22, 2005 06:42 AM
    You were fortunate to have linux-wlan-ng modules included in your distribution. Those of us using PPC don't have it so easy.

    Having said that, it is not impossible to set up. I think I covered it in my blog pycs.net/users/0000337. The keys are:

    Use your package management tool to install kernel source, must be same version as your running kernel. Yellowdog users can do sudo yum install kernel-source.

    Get the linux-wlan-ng source. Follow the steps to install it. It will build your kernel module.

    Some of us have an old dhclient that will not work with devices like wlan0. It wants ethn. I easily built and installed a new dhcp from ISC. The new version accepts devices like wlan0.

    Make a little file called wistart or something:<nobr> <wbr></nobr>/sbin/modprobe prism2_usb
    sleep 10<nobr> <wbr></nobr>/sbin/dhclient wlan0

    Make it executable chmod +x wistart

    sudo<nobr> <wbr></nobr>./wistart

    It automatically grabs an access point and gets a dhcp address. That's it.

    You can follow the story's mods if it grabs your neighbor's access point or something.

    I wish someone had instructions up somewhere, it took me months to get it working. I was surprised that it was so easy in Yellowdog, as most people doing experimental things tend to be Debian'ers.

    Enjoy.

    #

    overloaded terminology

    Posted by: Anonymous Coward on January 22, 2005 10:09 AM
    At first I thought this was about Intel's Ultra-Wideband Bluetooth replacement called
    "Wireless USB": http://www.intel.com/pressroom/archive/releases/2<nobr>0<wbr></nobr> 040218corp_c.htm
    I thought "What?! Did this tech make it to production without me noticing?". Then I looked up
    the Linksys device and realized it was a USB WiFi (802.11) adaptor...
    Guess I didn't miss anything after all.

    #

    Re:overloaded terminology

    Posted by: Derge on January 23, 2005 04:48 AM
    Amen! He picked the wrong title for his little story. I thought he was talking about Wireless USB, not stupid USB Wi-Fi adaptors. And yes, a previous poster who suggested a wireless bridge is right on. Linksys WET11 and a bunch of others allows the computer to think it is just using normal ethernet.

    #

    Re:overloaded terminology

    Posted by: Lee Schlesinger on January 27, 2005 04:47 AM
    Per your comments, we changed the title.

    Lee Schlesinger,
    Executive Editor, NewsForge.com

    #

    No WPA?

    Posted by: Anonymous Coward on January 22, 2005 11:32 PM
    I wouldn't use a wireless LAN connection unless I could get WPA-PSK to work. WEP is just too easy to break.

    #

    Re:No WPA?

    Posted by: Anonymous Coward on January 24, 2005 10:41 AM
    I have this similar model mentioned in the article and on the box, it says that you can use wpa on it. As to whether or not it works is something that I would have to experiment with.

    #

    Why USB?

    Posted by: Anonymous Coward on January 23, 2005 02:07 AM
    Just curious: why did it have to be USB?

    #

    Re:Why USB?

    Posted by: Keith Winston on January 24, 2005 09:49 PM


    There was a choice between using a PCI or USB 802.11b adapter. The desktop PC did not have a PCMCIA slot.



    I mentioned in the article that I chose USB because I could use it in future machines, including a laptop if my next PC turned out to be a laptop.

    #

    ndiswrapper?

    Posted by: Anonymous Coward on January 24, 2005 08:07 PM
    Why not try ndiswrapper, ndiswrapper.sf.net.

    #

    Re:ndiswrapper?

    Posted by: Keith Winston on January 24, 2005 09:51 PM


    Ndiswrapper would be a good option if I had not been able to get the native drivers to work.

    #

    PrismGT Linux driver doesn't support WPA yet

    Posted by: Anonymous Coward on January 24, 2005 11:55 PM
    They're still working on WPA support according to this page:
    http://prism54.org/

    #

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