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Of course, there's always the odd issue of old microwaves and wireless telephone handsets interfering with Wi-Fi performance. And, in many areas, there's a fair chance that you're going to have to fight with some neighbors for a clear channel. This is not what I'm asking about. I'm curious to know what can be done when there is someone with an axe to grind, who has equipment capable of stomping all over your 2.4 GHz and/or 5 GHz radio space and a little too much free time on their hands.

Is there anything that can be done from a network architecture standpoint, to reduce the likelihood that such an attack will have a worthwhile effect on the performance of your Wi-Fi devices? What else can be done to reduce the impact?

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Sue them. Make your building into a Faraday cage. Use Wired connections. –  Brian Aug 31 '12 at 13:25
    
@Brian Depending on how they're operating, and in what jurisdiction, lawsuits may not be possible. FCC Part 15 requires that devices not cause harmful interference, but also requires that devices accept any interference received (including interference which may cause undesired operation). Operating under Part 15, as most Wi-Fi APs and related devices do, is essentially playing around in the Wild West of Wi-Fi. Putting a Faraday cage around a building is generally impractical. Same goes for wired connections, for some purposes. –  Iszi Aug 31 '12 at 13:29
    
In any case, lawsuits are by nature an after-the-fact measure. This question is about what you can do to prevent the attack from significantly impacting your network in the first place. –  Iszi Aug 31 '12 at 13:32
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Radio Frequency Interference (RFI) in the United States is addressed by the FCC. Attacking with RFI is known as jamming and can be quite effective. It is also a crime in the US and the FCC is equipped to deal with it. The physics of radio reception and transmission does not allow for a technical means of protecting commercial systems. –  zedman9991 Aug 31 '12 at 13:39
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@Iszi: In the US, what they were doing would constitute harmful interference. There really isn't that much you can do about interference. Consider: People already talk about the difficulties of countering accidental interference, yet it are not fully successfully. Deliberate interference is always going to be at least as difficult as countering accidental interference. –  Brian Aug 31 '12 at 13:41
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4 Answers

Ha. I pictured a DoS at the physical level as someone holding your laptop out of arms reach from you.

who has equipment capable of stomping all over your 2.4 GHz and/or 5 GHz radio space and a little too much free time on their hands.

As stated by others:

Increase the signal sensitivity and noise isolation:

  • increase the signal power
  • increase the gain in a certain direction (directional antennas)
  • Isolate the noise: Shield your house from the jammer

However, I at least on 802.11b, it used to be easy to jam using Layer 2 which is a much easier DoS than pumping out interference.

If the person is jamming as bad as you say, they are probably violating some part of the FCC regulations; especially if they are jamming all of the 2.4 and 5Ghz spectrum. If they are targeting your SSID, you should put a fake AP on channel 1 with an obvious reference to your house and put a much weaker AP (turn down the power) on channel 11 named: "Bank of America" or something like that.

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One of the two technologies used in the early 802.11 days was Direct Sequence Spread Spectrum - it had interest in military circles because it spread the signal across a wide range of frequencies with three key benefits:

  • very low signal base, making it very difficult to identify the signal in amongst RF noise
  • Resistance to intended or unintended jamming, meaning you would need to jam a wide range of frequencies in order to stop the signal
  • Sharing of a single channel among multiple users

Another solution is to use highly directional antennas - narrow point to point links require an attacker to get close to that line of sight in order to impact the signal path.

Now this may not be useful for you at a home network level, but for a home network you have very simple options - run ethernet or use powerline technology. Can be deployed within minutes.

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+1. It's incredibly difficult to jam directional signals without being in close proximity to the device. If you're 50m away, the signal strength required would knock out the local neighbourhood's wifi! –  Polynomial Aug 31 '12 at 15:15
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Unfortunately, radio signal is radio signal. If it is at or near the same frequency, its kind of like trying to talk at a rock concert. The air space is so noisy that any meaningful signal is lost. The options are to talk over the noise (requires special equipment and is illegal in many jurisdictions to increase the power too much, build a Faraday cage as previously suggested (which would block out the noise and all other outside signals at the wavelength - cool demo on that, put your phone in the microwave and watch the signal disappear, (just don't turn ON the microwave), use directional antennas to try and filter out the noise (this is really kind of a different variant of the first option since a directional signal at the same power will be easier to pick up especially if you have a directional receiver pointed at it and not the source of the jamming.)

Outside of those options, I'm not really sure of much else in the way of jamming countermeasures, which is really what you are talking about. It would also depend if they are jamming all frequency channels as there are 11 to 13 frequency channels available depending on jurisdiction.

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You can try to build Faraday cages; this would require the WiFi access point and the authorized clients to be inside the cage, while the vindicative attacker would be on the outside. The Faraday cage should be a mesh with rings substantially smaller than the wavelength of the signal which is to block (radio-astronomers would recommend a factor of 10): 5 GHz means a 6 cm wavelength, so the mesh should ideally be as small as 6 mm -- which is doable but certainly not discreet, and unlikely to work well with any tasteful interior decoration.

Threats and dissuasion will probably work better. Invest in some radio goniometers which can pinpoint the location of the bad guy -- and let it be known that you would not hesitate to send policemen or hired thugs to enforce radio silence.

Alternatively, switch back to wired ethernet. This also solves many configuration headaches: wired ethernet "just works" and will offer better bandwidth (unfortunately, many cool-looking gadgets no longer offer ethernet: there is no ethernet plug in an iPad...).

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Several cool-looking android tablets support wired ethernet, typically with an add on rj45 to USB connector e.g., transformer prime -- however this is at the cost of mobility one of the major benefits of tablets. Apple seems to have no interest in allowing networking through their dock connector. –  dr jimbob Aug 31 '12 at 14:01
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+1 for "...or hired thugs". This is the first time I've heard of foxhunting tools being called "radio goniometers" though. –  Iszi Aug 31 '12 at 14:10
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+1 on this. I have built a 2.4GHz jammer, and a Faraday cage that defeats it. It's certainly not pretty, but I was able to get a USB wifi dongle and AP to talk to each other inside the cage. Without the cage, the jammer did its job, even when the dongle was ~10cm from the AP. If I were building a house to withstand external 2.4GHz / 5GHz jamming attacks, I'd build grounded wire meshes into the external wall cavities. Whilst windows are an obvious vulnerability, it'd severely hinder most attacks. –  Polynomial Aug 31 '12 at 15:11
    
There is also RF shielding paint and paint additives. I have never used one, so I can't recommend any. –  w.c Aug 31 '12 at 22:57
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