7 ms·

As a Wi-Fi networking engineer who often scratches his head at a lot of the software posts on HN, it is super fun to be on the other side and see the types of c

As a Wi-Fi networking engineer who often scratches his head at a lot of the software posts on HN, it is super fun to be on the other side and see the types of comments being thrown around by you lot. Also FYI you can rest assured that if you've engaged a semicompetent Wi-Fi professional to design the coverage in your office/campus/warehouse/etc then you don't need to worry about "the DFS problem" as it is well known and will have been accounted for in the design.

suction 4y ago
[dead]
walrus01 4y ago
In my experience as an ISP 95% of small businesses have no money or inclination to hire someone such as yourself to architect their LAN, sadly, resulting in worse results for them. They just buy whatever has more spikey antennas at best buy and hope it works.
wheybags 4y ago
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!
- 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.
yardstick 4y ago
> then you don't need to worry about "the DFS problem" as it is well known and will have been accounted for in the design. What does this mean? The DFS check doesn’t exist? Or they just reboot nearby devices several minutes apart to allow enough time for DFS to complete?
- jhartwig 4y ago
  I was wondering the same. What does a 'competent professional' do differently here?
  - McNutty 4y ago
    Put simply there will be two aspects taken into account in the 5GHz Wi-Fi design. Firstly, a coverage aspect of the design which will ensure that any given spot has a primary and secondary (and sometimes tertiary) AP radio providing appropriate RSSI. Secondly, a channel plan that ensures that the DFS channels are not allocated to the primary and secondary radios. So if a client station's primary AP get taken offline for a minute by DFS then that station can immediately roam to the stable channel and maintain a decent RSSI. Additionally, there may be some environments where the DFS channels are not enabled on the equipment at all. For example, many cheaper devices (think low end android phones) don't support DFS channels at all, so if there are many such devices in the area (e.g. College campus populated by poor students) then every radio running a DFS channel is effectively a coverage hole and therefore better to not use those channels at all. obtaining the govt certifications for using DFS channels does add to the cost of the chipset so cheapest chipset simply don't do it.
  - TrueDuality 4y ago
    Not all 5Ghz channels are affected by the DFS requirement. The DFS channels are more country specific than other WiFi band frequency restrictions. Usually the best course of action (or at least the one my coworkers and myself take) is to simply deny the band plan the use of those channels. A lot of consumer routers I've seen don't even expose the DFS channels as an option to avoid this problem (looking at you Motorola mesh products). It's not a problem just kind of funny to see.
- 4y ago
lifeisstillgood 4y ago
As someone who just "plugs and hopes" what steps should one take in building a small network - from running basic scans to see what else is in the area, strengths, and simply going "screw it lay down some cable" What's the best practise in other words
- patrakov 4y ago
  The trick is to choose a list of potential noise-free channels in the 5 GHz band, instead of one channel. Ideally channels that require DFS in at least one country, because a lot of cheap customer-grade network equipment (other than wireless cards) has them hard-disabled. E.g. TP-Link Archer C7 cannot be set to channel 56 using the stock firmware, even though the hardware itself is perfectly capable of transmitting on this channel and of radar detection. In short, DFS channels are good because you know your neighbors will not be using them. Then install OpenWrt (even on that TP-Link Archer C7 if you want), set "channels" to the list of channels that you identified (unfortunately this property is available only from the command line), and "channel" to auto. Then OpenWrt will select one of these channels after a one-minute delay, and jump away (but only to another known-good channel) if there is a radar.
jiggawatts 4y ago
In the software world we call the overall phenomenon in the article a leaky abstraction. We all pretend that WiFi is this magic thing that allows our devices to transmit data, but in fact there are all these little details of reality "leaking through" that abstraction. For example, it seems that instead of power cycling everything at once, WiFi should be turned on first to ensure that there is sufficient time for 5 GHz to be available. I sometime reboot my TV, Router, WiFi, and set-top-box simultaneously by simply turning the power board they're all connected to off and on. From now on I'll do them separately and in sequence...
- topranks 4y ago
  I’m not really sure it’s a “leaky abstraction”. Technical detail or something, I fail to see how it’s an abstraction to have this constraint in the WiFi standard.
- codazoda 4y ago
  I started doing this about a year ago. Not because it takes longer to boot up, but because I was trying to see which single device was most often the solution. In my setup there is a fiber modem (outside the house), a Wi-Fi router, and then all the connected devices. Oddly, the one that I need to restart the most, seems to be my Mac. Realizing, of course, the problem could still be on the router side, but turning wifi on and off on the laptop usually solves my problem. I rebooted one device at a time for about a year and made notes about each failure. I didn’t see the pattern until I had done this for a long time.
  - salawat 4y ago
    I am not impressed with Macbooks networking, or specifically the wireless on the Intel Macs. I've gone through three and ended up with such severe wifi issues, that I inevitably ended up switching to a wired dongle for anything serious/in need of stability. Never really had a more fickle laptop as far as wireless goes. Only a VAIO VPCZ1 after ten years of abuse as a gaming machine/daily driver started to get close. Again though, that's after 10 years. A Macbook will manifest that behavior within the first year for me. The frustration has gotten me to the point I'm reading up on USB/PCI-E/datasheets implementation/protocol details so I can actually try figuring out WTF could be the cause.
bmitc 4y ago
Do you have a reference or setup guide that walks you through best practices on how to most efficiently setup a home WiFi network?

suction 4y ago

[dead]

walrus01 4y ago

In my experience as an ISP 95% of small businesses have no money or inclination to hire someone such as yourself to architect their LAN, sadly, resulting in worse results for them. They just buy whatever has more spikey antennas at best buy and hope it works.

wheybags 4y ago

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!
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.

yardstick 4y ago

> then you don't need to worry about "the DFS problem" as it is well known and will have been accounted for in the design. What does this mean? The DFS check doesn’t exist? Or they just reboot nearby devices several minutes apart to allow enough time for DFS to complete?

jhartwig 4y ago
I was wondering the same. What does a 'competent professional' do differently here?
- McNutty 4y ago
  Put simply there will be two aspects taken into account in the 5GHz Wi-Fi design. Firstly, a coverage aspect of the design which will ensure that any given spot has a primary and secondary (and sometimes tertiary) AP radio providing appropriate RSSI. Secondly, a channel plan that ensures that the DFS channels are not allocated to the primary and secondary radios. So if a client station's primary AP get taken offline for a minute by DFS then that station can immediately roam to the stable channel and maintain a decent RSSI. Additionally, there may be some environments where the DFS channels are not enabled on the equipment at all. For example, many cheaper devices (think low end android phones) don't support DFS channels at all, so if there are many such devices in the area (e.g. College campus populated by poor students) then every radio running a DFS channel is effectively a coverage hole and therefore better to not use those channels at all. obtaining the govt certifications for using DFS channels does add to the cost of the chipset so cheapest chipset simply don't do it.
- TrueDuality 4y ago
  Not all 5Ghz channels are affected by the DFS requirement. The DFS channels are more country specific than other WiFi band frequency restrictions. Usually the best course of action (or at least the one my coworkers and myself take) is to simply deny the band plan the use of those channels. A lot of consumer routers I've seen don't even expose the DFS channels as an option to avoid this problem (looking at you Motorola mesh products). It's not a problem just kind of funny to see.
4y ago

lifeisstillgood 4y ago

As someone who just "plugs and hopes" what steps should one take in building a small network - from running basic scans to see what else is in the area, strengths, and simply going "screw it lay down some cable" What's the best practise in other words

patrakov 4y ago
The trick is to choose a list of potential noise-free channels in the 5 GHz band, instead of one channel. Ideally channels that require DFS in at least one country, because a lot of cheap customer-grade network equipment (other than wireless cards) has them hard-disabled. E.g. TP-Link Archer C7 cannot be set to channel 56 using the stock firmware, even though the hardware itself is perfectly capable of transmitting on this channel and of radar detection. In short, DFS channels are good because you know your neighbors will not be using them. Then install OpenWrt (even on that TP-Link Archer C7 if you want), set "channels" to the list of channels that you identified (unfortunately this property is available only from the command line), and "channel" to auto. Then OpenWrt will select one of these channels after a one-minute delay, and jump away (but only to another known-good channel) if there is a radar.

jiggawatts 4y ago

In the software world we call the overall phenomenon in the article a leaky abstraction. We all pretend that WiFi is this magic thing that allows our devices to transmit data, but in fact there are all these little details of reality "leaking through" that abstraction. For example, it seems that instead of power cycling everything at once, WiFi should be turned on first to ensure that there is sufficient time for 5 GHz to be available. I sometime reboot my TV, Router, WiFi, and set-top-box simultaneously by simply turning the power board they're all connected to off and on. From now on I'll do them separately and in sequence...

topranks 4y ago
I’m not really sure it’s a “leaky abstraction”. Technical detail or something, I fail to see how it’s an abstraction to have this constraint in the WiFi standard.
codazoda 4y ago
I started doing this about a year ago. Not because it takes longer to boot up, but because I was trying to see which single device was most often the solution. In my setup there is a fiber modem (outside the house), a Wi-Fi router, and then all the connected devices. Oddly, the one that I need to restart the most, seems to be my Mac. Realizing, of course, the problem could still be on the router side, but turning wifi on and off on the laptop usually solves my problem. I rebooted one device at a time for about a year and made notes about each failure. I didn’t see the pattern until I had done this for a long time.
- salawat 4y ago
  I am not impressed with Macbooks networking, or specifically the wireless on the Intel Macs. I've gone through three and ended up with such severe wifi issues, that I inevitably ended up switching to a wired dongle for anything serious/in need of stability. Never really had a more fickle laptop as far as wireless goes. Only a VAIO VPCZ1 after ten years of abuse as a gaming machine/daily driver started to get close. Again though, that's after 10 years. A Macbook will manifest that behavior within the first year for me. The frustration has gotten me to the point I'm reading up on USB/PCI-E/datasheets implementation/protocol details so I can actually try figuring out WTF could be the cause.

bmitc 4y ago

Do you have a reference or setup guide that walks you through best practices on how to most efficiently setup a home WiFi network?