Hack 26. Find and Join Wireless Networks with AP Radar

Use this handy GNOME application to find and join wireless networks.

From a purely functional perspective, the Wireless Tools included with Linux distributions are all you need to locate wireless networks. But as far as ease of use goes, they leave something to be desired. Unfortunately, most distributions do not install any other wireless tools.

AP Radar is an application designed to make wireless network detection and connection easier and more manageable. It is both a graphical network discovery tool and a wireless profile manager. Using the Wireless Extensions, it has the ability to watch for new networks while maintaining an association with your existing network. It automates connection tasks, so that when you come in range of your home network you are immediately associated.

2.5.1. Prerequisites

The program is the work of Don Park, and you can obtain source code from the project's development site at http://apradar.sourceforge.net. To compile successfully, you'll need to be running GNOME Version 2 or greater, and at least a 2.4.20 kernel. A 2.6 kernel is recommended.

AP Radar requires a wireless driver that is capable of running in Monitor mode. Most drivers support this mode, but there is an easy way to determine your driver's capabilities. Open a terminal and execute this command:

	iwlist ath0 scanning

You should see the following output:

	ath0		Scan completed :
				Cell 01 - Address: 00:02:2D:08:82:DA
				 ESSID:"foo"
				 Mode:Master
				 Frequency:2.442 GHz (Channel 7)
				 Quality=0/94 Signal level=-95 dBm Noise level=-95 dBm
				 Encryption key:off
				 Bit Rate:1 Mb/s
				 Bit Rate:2 Mb/s
				 Bit Rate:5 Mb/s
				 Bit Rate:11 Mb/s
				 Extra:bcn_int=100

If you see any other output, the chances are good that AP Radar will not function with your wireless driver.

There are also a number of packages that AP Radar requires to compile. Here are the Ubuntu or Debian packages that you can install with apt-get:

• libgtk-2.0
• libgtkmm-2.4.1
• libgtkmm-2.4-devel
• libiw-devel
• automake
• autoconf

RPM users can consult the README file in the source code for required RPM packages. The first two packages, libgtk and libgtkmm, should come installed by default in Ubuntu Linux.

2.5.2. Building and Using AP Radar

Once you have the necessary packages installed, you'll want to get the AP Radar source code from CVS:

cvs d:pserver:[e-mail]:/cvsroot/apradar login
		 cvs z3 d:pserver:[e-mail]:/cvsroot/apradar co P 
		 apradar

If prompted for a password during the CVS login, press Enter.

Once you're done, you'll have created an apradar directory. Change into the newly created directory, and execute these commands to configure and compile the source code:

sh autogen.sh
		 ./configure
		 make
		 make install

Assuming that you received no errors during compilation, this will place the AP Radar executable in /usr/local/bin/apradar. The program needs root privileges to run, and the best way to do that is with sudo:

	sudo apradar

If you experience problems starting AP Radar, they might be due to oddities in your wireless card driver and how it writes status to /proc/net/wireless. To avoid this problem, you can start the program by specifying the interface name:

	sudo apradari ath0

The program screen appears, as shown in Figure 2-19.

Figure 2-19. AP Radar

You should immediately see a list of all access points in range. Almost every field on the screen either is clickable or provides you with information when you hover the cursor over it.

To associate with any of the access points shown under Access Point List, click on the name of the network. By default, AP Radar associates your wireless card with the selected access point, but it also runs dhclient to obtain an IP address via DHCP.

DHCP and default gateway commands are accessed by clicking on the red symbol at the top left of the AP Radar screen:

 

Ping default gateway

This monitors the gateway set in the Linux route table. When AP Radar does not receive pings from this gateway, it assumes that the gateway is out of range.

 

Run dhclient -1 on associate

This allows you to specify whether you want AP Radar to obtain a DHCP address after it associates with an access point. Turn this off if you want static addressing.

2.5.3. Final Thoughts

AP Radar is an extremely handy little program that lets you simply join the wireless networks you need. It allows you to generally forget the Wireless Tools, unless you need to set specific wireless card parameters. What it doesn't do is provide anything in the way of diagnostic information on your wireless connectionno signal-to-noise information or any graphical display of network strength. Take a look at Kismet [Hack #29] or Wavemon [Hack #30] if you need more detailed wireless network information.