Книга: Fedora™ Unleashed, 2008 edition

Support for Wireless Networking in Fedora

Support for Wireless Networking in Fedora

The Linux kernel that ships with Fedora provides extensive support for wireless networking. Related wireless tools for configuring, managing, or displaying information about a wireless connection include the following:

iwconfig — Sets the network name, encryption, transmission rate, and other features of a wireless network interface

iwlist — Displays information about a wireless interface, such as rate, power level, or frequency used

iwpriv — Uses i to set optional features, such as roaming, of a wireless network interface

iwspy — Shows wireless statistics of a number of nodes

Support varies for wireless devices — most likely in the form of a PCMCIA adapter — although some USB wireless devices now work with Linux. In general, Linux wireless device software (usually in the form of a kernel module) supports the creation of an ethernet device that can be managed by traditional interface tools such as ifconfig — with wireless features of the device managed by the various wireless software tools.

For example, when a wireless networking device is first recognized and initialized for use, the driver will most likely report a new device:

wvlan_cs: WaveLAN/IEEE PCMCIA driver v1.0.6
wvlan_cs: (c) Andreas Neuhaus <andy@fasta.fh-dortmund.de>
wvlan_cs: index 0x01: Vcc 3.3, irq 3, io 0x0100-0x013f
wvlan_cs: Registered netdevice eth0
wvlan_cs: MAC address on eth0 is 00 05 5d f3 1d da

This output (from the dmesg command) shows that the eth0 device has been reported. If DHCP is in use, the device should automatically join the nearest wireless subnet and be automatically assigned an IP address. If not, the next step is to use a wireless tool such as iwconfig to set various parameters of the wireless device. The iwconfig command, along with the device name (eth0 in this example), shows the status:

# iwconfig eth0
eth0 IEEE 802.11-DS ESSID:"GreyUFO" Nickname:"Prism I"
     Mode:Managed Frequency:2.412GHz Access Point: 00:02:2D:2E:FA:3C
     Bit Rate:2Mb/s Tx-Power=15 dBm Sensitivity:1/3
     RTS thr:off Fragment thr:off
     Encryption key:off
     Power Management:off
     Link Quality:92/92 Signal level:-11 dBm Noise level:-102 dBm
     Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
     Tx excessive retries:0 Invalid misc:4 Missed beacon:0

This example shows a 2Mbps connection to a network named GreyUFO. To change a parameter, such as the transmission rate, use a command-line option with the iwconfig command, like so:

# iwconfig eth0 rate 11M

Other options supported by the iwconfig command include essid, used to set the NIC to connect to a specific network by named; mode, used to enable the NIC to automatically retrieve settings from an access point or connect to another wireless host; or freq, to set a frequency to use for communication. Additional options include channel, frag, enc (for encryption), power, and txpower. Details and examples of these options are in the iwconfig manual page.

You can then use the ifconfig command or perhaps a graphical Fedora tool to set the device networking parameters, and the interface will work as on a hardwired LAN. One handy output of the iwconfig command is the link quality output, which can be used in shell scripts or other graphical utilities for signal monitoring purposes (refer to Chapter 15, "Remote Access with SSH," for an example).

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