* Security sensor placement considerations
If you are planning to deploy a Wi-Fi intrusion detection/prevention system, how do you know where to place your sensors and how many of them to install?
Sensors, of course, are the distributed wireless devices that continually scan all Wi-Fi channels. They are looking for unauthorized devices that might be connected to your network, exposing it to denial-of-service attacks and malicious hacking.
So do you just toss a few sensors up in the ceiling, cross your fingers, and hope for the best? That’s one approach. Consider, though, that you’ll want your facility fairly well blanketed with sensor coverage, which might actually entail installing more sensors than you have access points (AP).
One reason is that the areas where you have installed no or few APs might be the very place a well-meaning (but compliance-busting) employee might plug in a home-bought AP for his or her own wireless convenience. Another reason is that – unlike with AP placement – some sensor “spillage” of radio signals outside the bounds of the corporate walls is actually desirable. This will allow detection of unauthorized devices lurking just outside corporate limits that are attempting to listen in.
Note, too, that APs don’t always blast at maximum power, so you want to be sure that the sensors can detect all of them. A clever hacker, for example, might bring in an unauthorized AP with the transmit power turned down to, say, 1 milliwatt, which would be difficult for a sensor more than a few feet away to detect. (Most 802.11-based networks transmit at about 30mW to 100mW, depending on the type of network – 11a, 11g, 11b, for example – and the transmit power regulations of the country in which they are operating.)
Also, account for anything that affects range and coverage, including the layout of your facility and the materials of floors, walls, ceilings, and windows.
