Wireless Tools

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To avoid having different configuration options for each make of wireless device, most wireless devices currently support the Wireless Extensions. These extensions provide a standard format for configuring all wireless devices. With the same set of configuration options, you can configure any wireless device that supports Wireless Extensions. The Wireless Tools package is a set of network configuration and reporting tools for wireless devices installed on a Linux system. They are currently supported and developed as part of the Linux Wireless Extension and Wireless Tools Project, an open source project maintained by Hewlett-Packard.

Wireless Tools consists of the configuration and report tools listed here:

Tool	Description
iwconfig	Sets the wireless configuration options basic to most wireless devices
iwlist	Displays current status information of a device
iwspy	Sets the list of IP addresses in a wireless network and checks the quality of their connections
iwpriv	Accesses configuration options specific to a particular device

The wireless LAN device will have an Ethernet name just like an Ethernet card. The appropriate modules will automatically be loaded, listing their aliases in the /etc/modules.conf file (see Chapter 32).

iwconfig

The iwconfig command works much like ifconfig, configuring a network connection. It is the tool used by the Internet Connection Wizard and by redhat-config-network to configure a wireless card. Alternatively, you can run iwconfig directly on a command line, specifying certain parameters. Added parameters let you set wireless-specific features such as the network name (nwid), the frequency or channel the card uses (freq or channel), and the bit rate for transmissions (rate). See the iwconfig Man page for a complete listing of accepted parameters. Some of the commonly used parameters are listed in Table 5-3.

Table 5-3: Commonly Used Parameters

Parameter	Description
essid	A network name
freq	The frequency of the connection
channel	The channel used
nwid or domain	The network ID or domain
mode	The operating mode used for the device, such as ad hoc, managed, or auto. Ad Hoc = one cell with no access point, Managed = network with several access points and supports roaming, Master = the node is an access point, Repeater = node forwards packets to other nodes, Secondary = backup master or repeater, Monitor = only receives packets
sens	The sensitivity, the lowest signal level at which data can be received
key or enc	The encryption key used
frag	Cut packets into smaller fragments to increase better transmission
bit or rate	Speed at which bits are transmitted. The auto option automatically falls back to lower rates for noisy channels
ap	Specify a specific access point
power	Power management for wakeup and sleep operations.

For example, to set the channel used for the wireless device installed as the first Ethernet device, you would use the following, setting the channel to 2:

iwconfig eth0 channel 2

You can also use iwconfig to display statistics for your wireless devices, just as ifconfig does. Enter the iwconfig command with no arguments or with the name of the device. Information such as the name, frequency, sensitivity, and bit rate is listed. Check also /proc/net/wireless for statistics.

Instead of using iwconfig directly to set parameters, you can specify them in the wireless device's configuration file. The wireless device configuration file will be located in the /etc/sysconfig/network-scripts directory and given a name like ifcfg-eth1, depending on the name of the device. This file will already contain many iwconfig settings. Any further setting can be set by assigning iwconfig values to the IWCONFIG parameter as shown here.

IWCONFIG="rate 11M"

iwpriv

The iwpriv command works in conjunction with iwconfig, allowing you to set options specific to a particular kind of wireless device. With iwpriv, you can also turn on roaming or select the port to use. You use the private-command parameter to enter the device-specific options. The following example sets roaming on:

iwpriv eth0 roam on

iwspy

Your wireless device can check its connection to another wireless device it is receiving data from, reporting the quality, signal strength, and noise level of the transmissions. Your device can maintain a list of addresses for different devices it may receive data from. You use the iwspy tool to set or add the addresses that you want checked. You can list either IP addresses or the hardware versions. A + sign will add the address, instead of replacing the entire list:

iwspy eth0 +192.168.2.5

To display the quality, signal, and noise levels for your connections, you use the iwspy command with just the device name:

iwspy eth0

iwlist

To obtain more detailed information about your wireless device, such as all the frequencies or channels available, you use the iwlist tool. Using the device name with a particular parameter you can obtain specific information about a device, including the frequency, access points, rate, power features, retry limits, and the encryption keys used. You can use iwlist to obtain information about faulty connections. The following example will list the frequencies used on the eth0 wireless device.

iwlist eth0 freq 

linux-wlan

The linux-wlan project (www.linux-wlan.org) has developed a separate set of wireless drivers designed for Prism-based wireless cards supporting the new 802.11 wireless standard. The linux-wlan drivers are not currently included with Red Hat. You will have to download the drivers. You can download RPM packages from people.redhat.com that include a base package, a modules packages, and packages for different kinds of hardware like PCMCIA or USB. You can also download RPM packages for specific kernels from prism2.unixguru .raleigh.nc.us.

The original source code package is available from the wlan-linux site at www.linux- wlan.org. The current package is linux-wlan-ng. You will have to unpack and compile the drivers as noted for source code software packages in the preceding chapter.

The drivers will install WLAN devices, with device configurations placed in the /etc/sysconfig/network-scripts directory. For example, the configuration for the first WLAN device will be in the ifcfg-wlan0 script. General wireless options are placed in the /etc/wlan.conf configuration file.

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