6 ms·

As a total amateur when it comes to electronics, let alone radio, what do you think would be the consequences if one were to hack their openwrt router to ignore

As a total amateur when it comes to electronics, let alone radio, what do you think would be the consequences if one were to hack their openwrt router to ignore dfs and just use the reserved channels without checking for radar? Not on a huge corporate network, just something like a single suburban home. Would the interruptions from interference of radar be less intrusive than the drops from changing channel? And is that sort of violation the kind of thing your local regulator would be scanning for and send someone out to shut you down? Obviously it would be illegal, and I promise I'm not gonna do it whatever your answer is :p

quetzthecoatl 4y ago
even if you set a dfs channel manually (editing hostapd config or cli) if you are using qualcomm/atheros or broadcomm chipsets, they will automatically move you out once it detects radar. At least with QCA/Atheros chipsets they used to have both compiletime and runtime flags to enable/disable most features (including dfs). Also, FCC fines are huge when it comes to dfs violation - as dfs spectrum is for emergency communication (military, natural disasters etc). There are radar simulators with which you can test this.
nine_k 4y ago
Radars are pretty good at locating things. So, if that rogue wifi device interferes much enough to be noticed by the radar operator on some nearby airfield, the reaction from radio authorities will likely be swift.
- wkat4242 4y ago
  This is not how it works. The AP is not actually responding to or reflecting the radar ping so the range detection won't work. If it even sees it it'll show up as a line from the center of the radar screen in the direction of the AP. It won't pinpoint it. But most likely it'll just add to the noise floor. It'll still be possible to locate it with that info but it's more work unless you manage to interfere with two radars and they can triangulate. That's pretty unlikely for an indoor access point with only a few milliwatts though.
  - rini17 4y ago
    I saw meteorologists publicly shame rogue APs by name. This implies they do have means (directional antenna) to probe the source of interference and get information such as AP name, MAC address and distance. https://www.shmu.sk/sk/?page=2037 https://www.shmu.sk/sk/?page=2037
    - Jenda_ 4y ago
      Radar receivers have a secondary output (or at least a waveguide coupler) where you can connect arbitrary equipment. So you connect standard wifi card to it, enable monitor mode and listen to all the MAC addresses and SSIDs (if they are not hidden) - directly though the giant radar antenna. (I really need to try it with our radar, I currently only detect packets based on their wide spectrum, but I have never decoded them) There is even a software-based wifi demodulator (https://www.nuand.com/bladerf-wiphy/ https://www.nuand.com/bladerf-wiphy/) so you can try to decode it from the IQ data, but they usually don't have enough bandwidth.
    - wkat4242 4y ago
      They wouldn't get this from the actual radar though. It must have been the result of further investigation. I was mainly referring to the 'radars are good at pinpointing things' comment from the OP :) I wanted to clarify that an AP on this frequency won't show up as a dot on a radar screen. For the distance to be captured it must have an actual reflection. You can even see some of the lines I mentioned in that pic!
  - formerly_proven 4y ago
    The way this works is someone notices a disruption and notifies the relevant authorities, which have detector vans to track down the emission sources. And they're quite good at that, too.
    - wkat4242 4y ago
      Indeed, I just wanted to clarify that the radar itself won't identify you as a 2D dot just like that. It needs further investigation.
hansel_der 4y ago
> Would the interruptions from interference of radar be less intrusive than the drops from changing channel? depends, hence the checking. > And is that sort of violation the kind of thing your local regulator would be scanning for and send someone out to shut you down? highly doubtfull
andreareina 4y ago
The interruption when the FCC knocks on your door would be pretty damn intrusive.
patrakov 4y ago
No need to hack anything. There are countries where DFS does not exist. Move there, install OpenWrt, set the country code appropriately in the GUI for both radios, enjoy both the fast WiFi and the good weather. And regarding the reasons for DFS - it is not due to the radars posing interference for access points, it is the other way round. They are supposed to be able to pick up reflections from clouds and airplanes that literally carry less than a millionth of the power that a typical AP would radiate.
- m4rtink 4y ago
  Here in the Czech Republic you used to be able to see clear "wedges" on meteoradar images due to these types of interference, but it seems to be mostly solved now.
aeonik 4y ago
FCC fines for violating radio spectrum rules are huge, and they are authorized to confiscate equipment as well. I wouldn't recommend it. Here is an example: https://www.fcc.gov/document/fcc-fines-hinson-dangerous-misuse-public-safety-radio-system-0 https://www.fcc.gov/document/fcc-fines-hinson-dangerous-misu...
- machinawhite 4y ago
  If I didn't see the post I would never think it's illegal. Also the FCC does not exist outside the US so is this relevant elsewhere?
  - lelandfe 4y ago
    https://en.wikipedia.org/wiki/Ignorantia_juris_non_excusat https://en.wikipedia.org/wiki/Ignorantia_juris_non_excusat > the FCC does not exist outside the US so is this relevant elsewhere? Your own country likely has an analogue. Get thee to Google. Ofcom is the UK equivalent, for instance.
    - Gordonjcp 4y ago
      Given that 5.8GHz WiFi and 5.8GHz weather radar are both licence-exempt services within an ISM band, you literally cannot pay Ofcom to take an interest.
      - richardhod 4y ago
        Given the level of corruption within the current UK government, I would not necessarily agree with your use of the word literally here. But at least in law and in principle yes.
        Gordonjcp 4y ago
        [flagged]
    - machinawhite 4y ago
karteum 4y ago
Well, you are both showing that you know it is illegal, yet asking "what would be the consequences ?". Of course if you get caught you would both have your hardware confiscated and experience a very severe fine (and possibly worse than just a fine if there were consequences in terms of interferences). People who operate radars (in particular radars for weather forecasts) are now really upset of the recurring interferences that come from wifi devices with (illegally) disabled DFS. Keep in mind that weather forecasts is not only about consumer people watching TV to know whether tomorrow will be sunny or rainy, but is also safety-related (e.g. for flights and navigation. You don't want your flight to be caught in a storm !). Those issues (significant interferences that are now almost impossible to solve) are periodically raising debates within RF administrations about whether to require locked hardware (locked bootloader and signed firmwares) in order to ensure that DFS cannot be disabled. That would be a pity for any embedded linux geek (openwrt is great both with regards to freedom, privacy, long-term support with security updates and therefore avoiding obsolescence, etc.), but a lot of people now think that it is the only way... I understand the shortcomings of DFS, yet you should really understand the 5 GHz wifi band is a band dedicated to radars as primary users where wifi has been tolerated under the condition of DFS, so wifi users should really not complain too much about the consequences and limitations of DFS (if there was no DFS, there would be no 5 GHz wifi band at all ! ;)
- stefan_ 4y ago
  No, there are plenty of modern weather radars now that have nothing to do with 5 GHz. This is a good example of how the FCC managing spectrum is the furthest thing possible from a good allocation; trillions of economic activity are driven by use of unlicensed bands, yet because there is nobody in particular ready to put up billions for a slice of spectrum, we end up with the FCC "design by committee" process for releasing them. That means whoever happened to be there is considered some sort of "lifetime incumbent" that must be worked around at all costs, even if their use of prime spectrum is absurdly wasteful. Challenged with the choice between "incur $ costs on few" or "incur $$$ costs on many", the FCC will consistently pick "incur $$$$ on all".
  - karteum 4y ago
jeroenhd 4y ago
Pick a channel outside the DFS range. Not every 5GHz channel is affected, only a subset of channels is. If you do cause interference with weather radar, there's actually a chance that the authorities take action. WiFi interference isn't hard to scan for at all, even or you disable broadcasting your SSID on the channels you're interfering on.

quetzthecoatl 4y ago

even if you set a dfs channel manually (editing hostapd config or cli) if you are using qualcomm/atheros or broadcomm chipsets, they will automatically move you out once it detects radar. At least with QCA/Atheros chipsets they used to have both compiletime and runtime flags to enable/disable most features (including dfs). Also, FCC fines are huge when it comes to dfs violation - as dfs spectrum is for emergency communication (military, natural disasters etc). There are radar simulators with which you can test this.

nine_k 4y ago

Radars are pretty good at locating things. So, if that rogue wifi device interferes much enough to be noticed by the radar operator on some nearby airfield, the reaction from radio authorities will likely be swift.

wkat4242 4y ago
This is not how it works. The AP is not actually responding to or reflecting the radar ping so the range detection won't work. If it even sees it it'll show up as a line from the center of the radar screen in the direction of the AP. It won't pinpoint it. But most likely it'll just add to the noise floor. It'll still be possible to locate it with that info but it's more work unless you manage to interfere with two radars and they can triangulate. That's pretty unlikely for an indoor access point with only a few milliwatts though.
- rini17 4y ago
  I saw meteorologists publicly shame rogue APs by name. This implies they do have means (directional antenna) to probe the source of interference and get information such as AP name, MAC address and distance. https://www.shmu.sk/sk/?page=2037 https://www.shmu.sk/sk/?page=2037
  - Jenda_ 4y ago
    Radar receivers have a secondary output (or at least a waveguide coupler) where you can connect arbitrary equipment. So you connect standard wifi card to it, enable monitor mode and listen to all the MAC addresses and SSIDs (if they are not hidden) - directly though the giant radar antenna. (I really need to try it with our radar, I currently only detect packets based on their wide spectrum, but I have never decoded them) There is even a software-based wifi demodulator (https://www.nuand.com/bladerf-wiphy/ https://www.nuand.com/bladerf-wiphy/) so you can try to decode it from the IQ data, but they usually don't have enough bandwidth.
  - wkat4242 4y ago
    They wouldn't get this from the actual radar though. It must have been the result of further investigation. I was mainly referring to the 'radars are good at pinpointing things' comment from the OP :) I wanted to clarify that an AP on this frequency won't show up as a dot on a radar screen. For the distance to be captured it must have an actual reflection. You can even see some of the lines I mentioned in that pic!
- formerly_proven 4y ago
  The way this works is someone notices a disruption and notifies the relevant authorities, which have detector vans to track down the emission sources. And they're quite good at that, too.
  - wkat4242 4y ago
    Indeed, I just wanted to clarify that the radar itself won't identify you as a 2D dot just like that. It needs further investigation.

hansel_der 4y ago

> Would the interruptions from interference of radar be less intrusive than the drops from changing channel? depends, hence the checking. > And is that sort of violation the kind of thing your local regulator would be scanning for and send someone out to shut you down? highly doubtfull

andreareina 4y ago

The interruption when the FCC knocks on your door would be pretty damn intrusive.

patrakov 4y ago

No need to hack anything. There are countries where DFS does not exist. Move there, install OpenWrt, set the country code appropriately in the GUI for both radios, enjoy both the fast WiFi and the good weather. And regarding the reasons for DFS - it is not due to the radars posing interference for access points, it is the other way round. They are supposed to be able to pick up reflections from clouds and airplanes that literally carry less than a millionth of the power that a typical AP would radiate.

m4rtink 4y ago
Here in the Czech Republic you used to be able to see clear "wedges" on meteoradar images due to these types of interference, but it seems to be mostly solved now.

aeonik 4y ago

FCC fines for violating radio spectrum rules are huge, and they are authorized to confiscate equipment as well. I wouldn't recommend it. Here is an example: https://www.fcc.gov/document/fcc-fines-hinson-dangerous-misuse-public-safety-radio-system-0 https://www.fcc.gov/document/fcc-fines-hinson-dangerous-misu...

machinawhite 4y ago
If I didn't see the post I would never think it's illegal. Also the FCC does not exist outside the US so is this relevant elsewhere?
- lelandfe 4y ago
  https://en.wikipedia.org/wiki/Ignorantia_juris_non_excusat https://en.wikipedia.org/wiki/Ignorantia_juris_non_excusat > the FCC does not exist outside the US so is this relevant elsewhere? Your own country likely has an analogue. Get thee to Google. Ofcom is the UK equivalent, for instance.
  - Gordonjcp 4y ago
    Given that 5.8GHz WiFi and 5.8GHz weather radar are both licence-exempt services within an ISM band, you literally cannot pay Ofcom to take an interest.
    - richardhod 4y ago
      Given the level of corruption within the current UK government, I would not necessarily agree with your use of the word literally here. But at least in law and in principle yes.
      - Gordonjcp 4y ago
        [flagged]
  - machinawhite 4y ago

karteum 4y ago

Well, you are both showing that you know it is illegal, yet asking "what would be the consequences ?". Of course if you get caught you would both have your hardware confiscated and experience a very severe fine (and possibly worse than just a fine if there were consequences in terms of interferences). People who operate radars (in particular radars for weather forecasts) are now really upset of the recurring interferences that come from wifi devices with (illegally) disabled DFS. Keep in mind that weather forecasts is not only about consumer people watching TV to know whether tomorrow will be sunny or rainy, but is also safety-related (e.g. for flights and navigation. You don't want your flight to be caught in a storm !). Those issues (significant interferences that are now almost impossible to solve) are periodically raising debates within RF administrations about whether to require locked hardware (locked bootloader and signed firmwares) in order to ensure that DFS cannot be disabled. That would be a pity for any embedded linux geek (openwrt is great both with regards to freedom, privacy, long-term support with security updates and therefore avoiding obsolescence, etc.), but a lot of people now think that it is the only way... I understand the shortcomings of DFS, yet you should really understand the 5 GHz wifi band is a band dedicated to radars as primary users where wifi has been tolerated under the condition of DFS, so wifi users should really not complain too much about the consequences and limitations of DFS (if there was no DFS, there would be no 5 GHz wifi band at all ! ;)

stefan_ 4y ago
No, there are plenty of modern weather radars now that have nothing to do with 5 GHz. This is a good example of how the FCC managing spectrum is the furthest thing possible from a good allocation; trillions of economic activity are driven by use of unlicensed bands, yet because there is nobody in particular ready to put up billions for a slice of spectrum, we end up with the FCC "design by committee" process for releasing them. That means whoever happened to be there is considered some sort of "lifetime incumbent" that must be worked around at all costs, even if their use of prime spectrum is absurdly wasteful. Challenged with the choice between "incur $ costs on few" or "incur $$$ costs on many", the FCC will consistently pick "incur $$$$ on all".
- karteum 4y ago

jeroenhd 4y ago

Pick a channel outside the DFS range. Not every 5GHz channel is affected, only a subset of channels is. If you do cause interference with weather radar, there's actually a chance that the authorities take action. WiFi interference isn't hard to scan for at all, even or you disable broadcasting your SSID on the channels you're interfering on.