Hack 27. Detect Networks on Mac OS X

Find out everything you ever wanted to know about the networks available in your area.

If you are simply looking for any available network, you can usually get by with the built-in AirPort software. However, if you are building your own network or troubleshooting wireless connections, you need much more detail than the standard tools provide. In particular, knowing which networks are in range and which channels they are using can be invaluable when determining where to put your own equipment. Here are two easy-to-use survey tools for Mac OS X that give you a far better idea of what's really going on.

2.6.1. MacStumbler

Sharing nothing but a name with the popular NetStumbler [Hack #24], MacStumbler (http://www.macstumbler.com) is the original network scanner for Mac OS X. It is simple to use, and it provides the details that you are most likely interested in: available networks, the channels they use, and their received signal strength. It also displays received noise, whether WEP is enabled, and a bunch of other useful details, as shown in Figure 2-20.

Figure 2-20. MacStumbler's main screen

Like many Mac OS X apps, MacStumbler is capable of text-to-speech, so it will speak the ESSIDs of networks that it finds as they appear. You can set the preferences to play different sounds when it detects an open network or a WEP network. MacStumbler also has GPS support, and can use GPS devices connected via serial or Bluetooth. With GPS support you can record the latitude and longitude of any access points. This feature is not only for wardriving; it is also very useful when mapping your outdoor wireless network.

Unfortunately, MacStumbler is three years oldthe last update was July 2003and it is showing its age. It supports only the Apple AirPort card, and no external PC Card or USB wireless devices. It also doesn't recognize WPA encrypted networks. Lastly, while MacStumbler does work on the latest 10.4 release of Mac OS X, there is no guarantee of future support, because development seems to have stopped.

2.6.2. iStumbler

A more up-to-date tool is iStumbler (http://istumbler.net). Just fire it up and it will find all available networks for you, complete with a real-time signal and noise meter. It scans Bluetooth and Bonjour networks and reports detailed information on both. It also works with both serial and Bluetooth-connected GPS units. Like MacStumbler, iStumbler supports scanning only when using the built-in AirPort card.

As shown in Figure 2-21, iStumbler's main window packs a lot of information into a small window. The menu on the left offers several monitoring options, including AirPort, Bluetooth, Bonjour, and GPS connections.

The connection monitor, which appears when you join a network listed in the AirPort section of iStumbler, is a nice feature. Figure 2-22 shows a sample window that you can make stay on top of other programs. You can adjust the transparency to your liking, so the monitor is always visible even if you are working on something else.

Figure 2-21. iStumbler's compact display

Figure 2-22. The handy connection monitor

iStumbler lets you join any listed AirPort network directly, without involving the AirPort configuration tools. Likewise, if you are monitoring Bluetooth, you can set up, pair with, or browse available Bluetooth devices. For Bonjour connections, there are options to connect to listed items.

A more powerful item is the Inspector, found in the Edit menu or by pressing Command-I. This is available for all modes in iStumbler, and it provides detailed information on the network or share that is highlighted in the main window. Figure 2-23 shows the detail taken by each sample of an 802.11g network.

2.6.3. Final Thoughts

Both of these tools will find all available Wi-Fi networks quickly and keep historical logs if you need to monitor wireless networks over time. If you need to find all available networks in range, either of these tools is ideal. iStumbler supports newer features of Mac OS X and is the better choice, particularly if you want to examine Bluetooth or Bonjour networks.

MacStumbler and iStumbler work by actively sending out probe requests to all available access points. The access points respond to the probes (as they would for any legitimate wireless client), and this information is then collected, sorted, and displayed by the scanners. Unfortunately, neither of these tools will find "closed" networks, because they don't respond to probe requests.

Figure 2-23. iStumbler Inspector

There is an unfortunate side effect caused by people who choose to hide their networks. Since it isn't easy to tell what channel they are using, it is likely that someone nearby will choose to use the same (or an adjacent) channel for their own network. This causes undesirable interference for everybody. To detect closed networks, you need a passive scanner, such as KisMAC [Hack #28].