Fight 802.11 Pollution!
If you’re in a public area right now with some sort of portable wireless device, take a quick look at the list of open wireless networks. Notice those ad-hoc (peer to peer) networks all over the place?
Connect to any of those, and you’ll find nothing other than someone else’s laptop. Perhaps some services will appear via Bonjour, Rendevous, or SMB announce thanks to ‘zero-configuration’ networking, but that’s all you’re going to find. Most likely, you will find one titled “Free Public WiFi”.
What is all this rubbish, and why is it there? The answer is pretty simple, really. The Windows operating system (which I do not use, for good reasons) remembers which wireless networks you were connected to permanently. This is probably a good thing, when you are connecting to ‘infrastructure’ networks with access points; it saves you from having to manually having to reselect the network each time you move from home to school, etc.
This behavior is at the very least stupid, and at the worst, disastrous, when applied to ad-hoc networks.
On an infrastructure network, the network is announced to and detected by the clients by the periodic transmission of a beacon frame. This beacon frame transmits some basic data, such as the network name. (If you’re curious as to exactly what’s in the beacon frame, there’s a nice article on that.)
On an ad-hoc network, every client transmits a beacon frame. Windows remembers to ‘connect’ to an unused ad-hoc network by beaconing… which essentially spams the airwaves with announcements of a network that goes nowhere.
This is, at the best, an inconvenient waste of power and source of interference to existing networks, and at the worst, a gaping security flaw.
Let me elaborate on the security concerns of this for a moment:
Remember the MS Blaster worm? The Blaster worm exploited a bug in the Windows networking stack to inject and execute its code, and to spread. An infected system with one of these wireless networks left on would immediately spread it to any other system that connected to it, probably because it too had been left on there.
Fortunately, the solution to this problem seems to be simple. Don’t connect to these junk networks, like ‘Free Public WiFi’, ‘hpsetup’, etc. Any business or home installation that offers free wireless Internet access will, almost without exception, have an access point. If you do connect to one of these, be sure to disconnect from it before moving to another location.
Mac users don’t have to worry about this; OS X won’t beacon an ad-hoc network unless you’ve chosen the “Create Network…” option. It’ll only connect to one it already sees beaconing.
You too can do your part to fight wireless LAN pollution! By making sure you’re not beaconing rubbish networks, you too can protect the world from the forces of evil!