Handbook:Parts/Networking/Wireless/ja

はじめに
Wireless networking on Linux is usually pretty straightforward. There are two ways of configuring wifi: graphical clients, or the command line.

The easiest way is to use a graphical client once a desktop environment is installed. Most graphical clients, such as wicd and NetworkManager, are pretty self-explanatory. They offer a handy point-and-click interface that gets users on a network in just a few seconds.

Wireless can also be configured from the command line by editing a few configuration files. This takes a bit more time to setup, but it also requires the fewest packages to download and install. Since the graphical clients are mostly self-explanatory (with helpful screen shots at their home pages), we'll focus on the command line alternatives.

There are two tools that support command-line driven wireless configurations: and. Of these two, is the preferred one. The important thing to remember is that wireless networks are configured on a global basis and not an interface basis.

The software supports nearly all cards and drivers, but it cannot connect to WPA-only Access Points. If the networks only offer WEP encryption or are completely open, then beats the other package over simplicity.

Some wireless cards are deactivated by default. To activate them, please consult the hardware documentation. Some of these cards can be unblocked using the rfkill application. If that is the case, use  to see the available cards and   to activate the wireless functionality. If not, then the wireless card might need to be unlocked through a button, switch or special key combination on the laptop.

WPA supplicant
The WPA supplicant project provides a package that allows users to connect to WPA enabled access points.

Next, configure so that the wpa_supplicant module is preferred over wireless-tools (if both are installed, wireless-tools is the default).

Next configure wpa_supplicant itself (which is a bit more tricky depending on how secure the Access Points are). The below example is taken and simplified from which ships with wpa_supplicant.

Initial setup and managed mode
The wireless tools project provides a generic way to configure basic wireless interfaces up to the WEP security level. While WEP is a weak security method it's still prevalent in the world.

Wireless tools configuration is controlled by a few main variables. The sample configuration file below should describe all that is needed. One thing to bear in mind is that no configuration means "connect to the strongest unencrypted Access Point" - wireless tools will always try and connect the system to something.

Fine-tune AP selection
It is possible to add some extra options to fine-tune the AP selection, but these are not required.

One way is to configure the system so it only connects to preferred APs. By default if everything configured has failed and wireless-tools can connect to an unencrypted Access Point then it will. This can be controlled by the associate_order variable. Here's a table of values and how they control this.

There is also the blacklist_aps and unique_ap selection. blacklist_aps works in a similar way to preferred_aps. unique_ap is a yes or no value that says if a second wireless interface can connect to the same Access Point as the first interface.

Ad-hoc and master modes
To set the system up as an ad-hoc node when it fails to connect to any Access Point in managed mode, use this as a fallback:

It is also possible to connect to ad-hoc networks, or to run the system in master mode so it becomes an access point itself.

Troubleshooting wireless tools
There are some more variables that can help to get the wireless up and running due to driver or environment problems. Here's a table of other things that can be tried.

Defining network configuration per ESSID
In this section, we show how to configure network settings based on the ESSID. For instance, with the wireless network with ESSID ESSID1 configure a static IP address while ESSID ESSID2 uses DHCP.