How to prevent wireless DoS attacks

I think it's because, um, YOU CAN'T! You simply cannot prevent a wireless DoS attack against the RF layer of the network.

Don't let wireless intrusion prevention system (WIPS) vendors fool you. You can detect a wireless denial of service (DoS) attack, but you cannot prevent it if it is an RF-level attack. Sure, if it's a frame level attack, you can prevent it through algorithms and dynamic network configuration management procedures. But if you're dealing with a physical level (RF) DoS attack, you can only remove it once the source is located – you cannot prevent it.

All I need is a 2.4 GHz RF generator and I can blanket the entire 2.4 GHz license free ISM band that is used by 802.11 b/g/n. With a 5 GHz RF generator, I could potentially do the same for the U-NII bands used by 802.11a/n. The point is that an RF generator or set of such generators can completely saturate the available spectrum with energy levels that prevent functional communications on any allowed channel. Dynamic channel management and "self-healing" solutions cannot help with this.

A good old fashioned human being with a spectrum analyzer is one of the best ways to locate a physical layer wireless DoS attack. WISP solutions may also be able to triangulate the source of the attack if sensors or multi-purpose access points (access points that both provide wireless functionality and sensing abilities) are used; however, it's not like the WIPS system can somehow zap the attacking device and kill it (though that's a nice thought for the future). The end result is that a physical layer DoS simply CANNOT be prevented. It can only be mitigated (i.e., the severity is reduced by detecting it quickly, locating it and eradicating it).

Personally, I find no greater joy in my IT work than tracking down an attacker and letting him see me with my spectrum analyzer as he flees in fear (and I memorize is license plate number to report him to the police). Would I really even want a software program and hardware set to take away that joy?

Inventors of the world, if you can find a true solution that truly prevents wireless denial of service attacks, you can make billions. Get started.

UPDATE: About an hour after first writing this post I was extremely annoyed by the following press release:

http://www.airtightnetworks.com/home/news/press-releases/pr/article/123/airtight-wireless-dos-attack-prevention-named-top-security-innovation-for-2009.html

Notice the press release uses the phrase DoS attack prevention, but then the actual press release admits frankly that all it does is "counter wireless DoS attacks". My point is still the same: On a wired network, you can immediately shut of the port from which a DoS attack is originating . This can be accomplished in just a few seconds. You cannot accomplish this today when a wireless DoS attack is launched against the entire unlicensed spectrum in which your wireless LAN operates. Please, vendors, just be honest and quit using the word prevent in relation to wireless DoS attacks!

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The wavelength is an important factor in wireless networking. The wavelength dictates the optimum size of the receiving antenna and it determines how the RF wave will interact with its environment. For example, an RF wave will react differently when it strikes an object that is large in comparison to the wavelength than when it strikes an object that is small in comparison to the wavelength.

The wavelength and the frequency are interrelated. For a given medium, if you know the wavelength, you can calculate the frequency and if you know the frequency, you can calculate the wavelength. The wavelength is directly related to the frequency and the speed of light. If you know the frequency, you can calculate the wavelength. If you know the wavelength, you can calculate the frequency.

One of the great discoveries in the history of electromagnetism is that electromagnetic waves travel at the speed of light. Since we know the speed of light to be 299,792,458 meters per second (or the simple 300,000,00 meters per second, if you prefer), we also know that this is the speed at which electromagnetic waves travel in a vacuum. This was theorized by James Clerk Maxwell and proved through experimentation by Heinrich Hertz.

You are probably familiar with measurements like 100 megahertz and 3.6 gigahertz. These measurements refer to the number of cycles per second. When we say that the access point is using the 2.45 GHz (gigahertz) spectrum, we say it is using the spectrum that uses a wave cycle rate of 2,450,000,000 times per second. This measurement is named for Heinrich Hertz and his research in electricity and magnetism. A kilohertz is 1,000 hertz or cycles per second. A megahertz is 1,000,000 hertz and a gigahertz is 1,000,000,000 hertz. A terahertz is one trillion hertz, but these frequencies are not commonly found in today’s wireless communications.

Since we know that RF waves travel at the speed of light we can calculate the frequency when we know the wavelength or the wavelength when we know the frequency. The following formula can be used to calculate the wavelength in meters when the frequency is known:

w = 299,792,458 / f

Where w is the wavelength in meters and f is the frequency in hertz and the medium is a vacuum. Therefore, the 2.45 GHz spectrum would have a wavelength that is calculated with the following formula:

w = 299,792,458 / 2,450,000,000

The result is .123 meters or approximately 12.3 centimeters in length. This translates to about 4.8 inches. To calculate inches from centimeters, just multiple the number of centimeters times 0.3937. The formal character used to represent a wavelength is the Greek lambda (λ), and the symbol for the speed of light is c. Therefore, the formal representation of the previous formula would be:

λ = c / f

The calculation for frequency is just the opposite. You will divide the speed of light by the wavelength in meters to discover the frequency. Keep in mind that the numbers we’ve been using have been rounded and that impacts the results of the following formula; however, the results are close enough to recognize that a wavelength of .123 meters would indicate a RF wave in the 2.45 GHz spectrum:

f = 299,792,458 / .123
f = 2437337056.91

Due to the complex measurement number that is the speed of light, this number is often rounded to 300 billion meters per second. While this will change formula results, the findings are close enough for understanding the behavior of RF waves; however, engineers developing RF systems must use more precise measurements. Additionally, formulas like the following simplify matters:

wavelength in inches (λ) = 11.811 / f (in GHz)
wavelength in centimeters (λ) = 20 / f (in GHz)

Because wireless networks use such high frequency ranges, formulas like this make the calculations easier.
 

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