Wireless Hacks

Hack 22 Network Detection 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 client. But if you are building your own network, or troubleshooting someone else's, you need much more detail than the standard clients 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 very easy-to-use survey tools for OS X that give you a far better idea of what's really going on.

MacStumbler

Sharing nothing but a name with the very popular NetStumbler [Hack #21], MacStumbler (http://www.macstumbler.com/) is probably the most popular network scanner for OS X. It is simple to use, and 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. See Figure 3-14.

Figure 3-14. MacStumbler's main screen.

Like many OS X apps, MacStumbler is capable of text-to-speech, so it will even speak the ESSIDs of networks that it finds as they appear. Although it is still in beta, I have found MacStumbler to be a very reliable tool. It currently supports network scanning using only the built-in AirPort card.

iStumbler

Another popular network discovery tool is iStumbler (http://homepage.mac.com/alfwatt/istumbler/). This tool is even simpler than MacStumbler, in that there is really nothing to configure. Just fire it up and it will find all available networks for you, complete with a real-time signal and noise meter.

As you can see in Figure 3-15, there are plans for GPS support in the next release, but as of v0.6b and at the time of this writing, the Coordinates field is meaningless. Like MacStumbler, iStumbler supports scanning only when using the built-in AirPort card.

Figure 3-15. iStumbler's simple, brushed metal interface.

These tools will both find all available networks quickly, and will 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 are ideal.

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, since they don't respond to probe requests. This is an unfortunate side effect for people who choose to hide their networks. Since it isn't easy to tell what channel they are using, it is very 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 #24] or Kismet [Hack #31].