13 ms·

Resolving an unusual WiFi issue

594 points by emidoots 4y ago

deleted 4y ago
[deleted]
zdw 4y ago
My most unusual wifi issue was on a system that said it had a great connection (SNR) and was running at high speed, but would just not pass traffic if it was further than about 1m from a base station. Turned out to have multiple antennas, and the transmit antenna was broken, so it could receive just fine, but not transmit over anything but short distances. Sometimes the physical layer is the problem, even if the logical layer says everything is fine.
- klysm 4y ago
  I guess the logic layer only said the receive side was fine. It can’t see what’s happening within the transmit antenna I don’t think
  - Nextgrid 4y ago
    I'm surprised there isn't a mechanism for the link peer to report the SNR to the sender from its perspective. I've had the same issue without any antenna troubles - Mac would constantly connect to the 5GHz network and struggle to send any packets out, yet the displayed signal strength was good. It turns out it was able to "hear" the AP just fine, but the AP had trouble hearing back, yet somehow there's no feedback mechanism for it to know.
    - klysm 4y ago
      A kind of SNR ping seems like it would make a lot of sense. I don’t know enough about radios but anybody know why that doesn’t exist?
      - sbierwagen 4y ago
        Wifi 6 has all sorts of active sensing stuff for spatial frequency reuse, but GP didn't say what generation of wifi equipment was being used.
      - ac29 4y ago
        The industrial (non-wifi) radios I use at work have a signal/noise ping function. Its very useful.
zionic 4y ago
Wow. This should be the kind of thing windows/your OS detects and warns you about.
- unnouinceput 4y ago
  Why? Since when your OS knows what you want to do? Maybe I do intent to enumerate wifi's around me every 10 seconds, so why would OS would be bothered to do such warning? Also Windows has event viewer, you can see there what's going on anyway (consider that the OS warning you want)
jtchang 4y ago
I believe this can happen on macos as well.
- LaputanMachine 4y ago
  In macOS there are also ping spikes when you open the WiFi menu bar [1]. This still happens in macOS Monterey. [1]: https://developer.apple.com/forums/thread/97805 https://developer.apple.com/forums/thread/97805
  - walrus01 4y ago
    If I had to guess it's because the system is temporarily pausing tdd wifi traffic while it scans the 2.4 and 5.x GHz bands to see what SSIDs are broadcasting. It is a bit of a trade off since if you want to see every possible available AP, even the shitty ones with signal levels at like -80, you can't be noisy on your own radio at the same time as you scan the band. Remember it's a half duplex medium. It does it even more if you hold down option and click the wifi menu bar, to get detailed signal strength/info on the AP you're presently connected to.
  - nicoburns 4y ago
    This seems more reasonable, given that: 1. I can't see how you'd enumerate wifi networks without degrading network performance. 2. The user has specifically initiated a wifi-related action. 3. There's not generally any need to use that menu unless the network is already not working.
- icedchai 4y ago
  I've seen this happen on my Mac desktop. I eventually found a post where someone mentioned turning off "find my mac" fixing it: https://developer.apple.com/forums/thread/97805?page=2 https://developer.apple.com/forums/thread/97805?page=2
deleted 4y ago
[deleted]
naikrovek 4y ago
I don't think I would have ever figured this out, if it happened to me. the very first thing I do when I have a problem on wifi, is to remove wifi from the equation. wired Ethernet is so much better, and so far, the problem always disappears.
- massysett 4y ago
  I had this exact same problem with Citrix Workspace. I tried disabling Wi-Fi scanning but had mixed results with that for some reason. Now I have bought a cheap Wi-Fi extender for maybe $30 and plugged my desktop’s Ethernet jack into it. So far this is working extremely well. I disabled the other Wi-Fi extending features of the extender, so essentially it’s a huge Wi-Fi to Ethernet dongle. I find it stupid that I have to employ such a janky solution to this. Citrix Workspace on the Mac does not have this problem, but using an old MacBook Pro for this was undesirable for various reasons.
AnotherGoodName 4y ago
Anyone ever had arp storms on a home network? I've had something trigger every device into asking 'who has xyz ip tell [Mac]'. It made the network unusable and even rebooting systems it would come back since as soon as one device asked the question (sent the broken arp packet) all other devices decided they too needed to know. The solution that worked was to flip the circuit breaker for the whole house and reset every network device at once.
- klysm 4y ago
  I haven’t had a problem where rebooting the house has fixed it thankfully
  - somat 4y ago
    I laughed, but it made me think, with "smart" houses becoming a thing, this will one day become a common occurrence. sigh
- mh- 4y ago
  Yes, generated by AT&T's wireless STBs (cable boxes) back around 2014-15. It was a nightmare to figure out, as I recall.
- dylan604 4y ago
  That takes did you turn it off and on again to an entirely different level. What if we need to do this city wide?
  - wizofaus 4y ago
    That sounds like a good plot for a movie - the day we had to reboot the entire internet...
    - Lammy 4y ago
      "South Park already did it": https://en.wikipedia.org/wiki/Over_Logging https://en.wikipedia.org/wiki/Over_Logging
chedabob 4y ago
Reminds of the issue on Mac OS where Location Services would cause ping spikes https://news.ycombinator.com/item?id=31356730 https://news.ycombinator.com/item?id=31356730
- hbn 4y ago
  Here's a spicy meatball for you: wifi lag spikes caused by placing an AirPlay button in the touchbar https://mnpn.github.io/blog/airplay-network-disaster https://mnpn.github.io/blog/airplay-network-disaster Previous discussion: https://news.ycombinator.com/item?id=31706283 https://news.ycombinator.com/item?id=31706283
  - m463 4y ago
    I wish I could decisively turn off airplay on macos. It's the source of so many weird issues. For example, locked down mac, using wifi at a friend's house and their LG tv shows up as an airplay mirroring device. Why should my machine be discovering that TV without me asking? When I'm on a public network, I'd like to make my machine output-only, not promiscuous in this way. there was also an issue where a macbook would randomly lose its onboard sound and somehow default to using a nearby appletv as the output device.
    - jabbany 4y ago
      > I'd like to make my machine output-only, not promiscuous in this way. The TV advertises itself on the network so it's the one being promiscuous. Your machine is still being passive, it just shows you the devices that are have advertised themselves. No idea about the sound thing though, I don't use any Mac stuff :)
    - month13 4y ago
      macOS is so frustrating at times, as there's some cool features that are gated by magic, so not only do they not work at times and offer no diagnostic resolutions, also cripple networks. I recall disabling the `awdl` adapter can stop a lot of this behavior, at the cost of breaking these systems. I used to do this when using Moonlight, as it would cause periodic ping spikes.
Fitilii 4y ago
brainzap 4y ago
I hate wifi issues so much, specially when you stream audio.
- wizofaus 4y ago
  Definitely my biggest bugbear with relying in streaming for music - it's the one thing I use apple hardware for (apple tv) and I can't even sync music to it anymore, plus there's no ability to control buffering that's worked so far. So I'm stuck with listening to music knowing it might stutter at any moment...
- Nextgrid 4y ago
  The main problem is that OSes do a terrible job at reporting Wi-Fi performance. RSSI is a very poor metric by itself, yet is all that's driving the wireless signal strength indicator. Most wireless links are constantly in a barely working mode that's only made usable by TCP and various retransmission/error-correction algorithms on top, so a lot of connections that people think are "fine" (especially when the signal strength meter is maxed out) are actually not fine at all. There is no magic and those workarounds don't work for real-time streams such as calls/games/etc, so those "fine" connections will crap out miserably as soon as users jump on a call or game. I'm not sure if there's a way for the OS to get any more info about the link quality/stability from the network card itself, but a purely software-level workaround could be to just track all TCP sessions (should be easy, as that's already managed by the kernel), average the percentage of retransmissions across all of them (to prevent a single bad server from skewing the result) and factor that into the "signal strength" meter. An easy way to test this yourself is to run a ping towards your default gateway (the IP of your router). You should see a consistently low latency (in the low single-digits range) and no packet loss. If you're seeing losses or significant variation in response times, your connection is bad and you should do something about it (get closer to the AP or install a second one).
valleyer 4y ago
Nice debugging. Do I understand correctly that the registry reads aren't actually the cause of the problem but rather just a signal that a QNetworkAccessManager is active and causing a scan? If so, is there a better routine to break on in the debugger to see it actually initiating a scan?
- muststopmyths 4y ago
  You can see a hint in the debugger screenshot. The call is not directly a registry read but to the iphelper API. There are functions in there that enumerate adapters. Knowing nothing about this scanning process, I’m just assuming they first enumerated wireless adapters. So you could start with iphelper and then explore deeper into how you tell the card to scan. There’s probably some API for that as well.
  - valleyer 4y ago
    Ah, good point. Wish the backtrace were fully symbolicated (for the system DLLs, at least). Thanks!
yellow_lead 4y ago
> At the exact same time the lag spikes occur, MBPP starts querying the registry keys for all of the network interfaces. Can anyone tell me why this causes the network issue? Don't understand how querying the registry can cause this.
- Arnavion 4y ago
  Querying the registry does not cause the issue. Querying the registry is a thing that Qt does as part of the code that causes the issue.
proactivesvcs 4y ago
I've got a customer enjoying this exact fault at the moment, what luck.
RicoElectrico 4y ago
The "proper" solution not depending on the application layer: https://www.reddit.com/r/GlobalOffensive/comments/3ahg59/fix_for_wireless_ping_spikes/ https://www.reddit.com/r/GlobalOffensive/comments/3ahg59/fix... Turn autoconfig back on only when you restart your PC or disconnect from the network (maybe someone can automate this by checking connectivity without scanning networks, enabling autoconfig, and then turning it back off)
networkwanderer 4y ago
I love these debugging stories but its a total nightmare to deal with these kinds of issues. At the moment there's this really weird network issue we're having where iPhones are unable to play Netflix on the Wifi. Every other device works fine but iphone 7, 8 (2 devices) and SE can't stream Netflix. I noticed there is other things they can't do, for example the page for the fast.com speedtest loads but the speedtest cant be performed. Same with the Google speedtest. The phones also can't access Apples update server on the wifi. Other network stuff does work fine, youtube works, browsing works, etc. The behaviour is consistent across the iphones and all these things work fine on multiple other devices on the same network. I can't make sense of it at all. Called internet provider and they didnt know either apparently other people had the same issue but nothing has changed from their side of things. Called Apple support and they are putting the blame on the network provider. Tested one of the devices on a different wifi network and works fine. AFAIK if you're an internet router the packets look the same no matter what device is being used so I think this must be some Apple software issue. Or maybe my router is cursed.
- mrb 4y ago
  I'm fairly confident you are victim of a PMTUD black hole. It's easily fixed by making your router force the TCP MSS to a slightly lower value. All your symptoms are explained by this (some but not all devices are affected, some but not all services are unreachable).
  - kalleboo 4y ago
    Yeah, not having an option to set the MTU was the reason I had to stop using the Apple AirPort Extreme when we moved to a new apartment, the symptoms were all the same as GP, limiting the MTU fixed it.
  - cryptonector 4y ago
    Or better yet, use packetization PMTUD. 15 years after that was published by the IETF, every device should implement it by default.
    - 4y ago
lobsterboix 4y ago
This is incredible, we use QT5.12 for an embedded device application, and this issue has been a really weird one for us and this spot on resolves it! See browsing HN at work does pay off!
- avg_dev 4y ago
  Haha, that’s excellent. Your coworkers will be happy I am sure. And I love a good debugging story myself.
- rurban 4y ago
  We should really upgrade our QT though
deleted 4y ago
[deleted]
josephcsible 4y ago
The "new, highly-reviewed, wifi adapter" pictured in the article looks like Alibaba garbage. I'm surprised it didn't cause some worse problem.
- jandrese 4y ago
  "Highly Reviewed" and it comes with a "leave a 5 star review for a kickback" offer. A card like that is grounds for returning the thing and leaving a 1 star review IMHO.
  - josephcsible 4y ago
    Amazon has made a habit lately of rejecting your review if you do that. It's like they want to help these scammers.
    - Nextgrid 4y ago
      Can you delete reviews? An alternative could be to take them up on the offer, post the review, cash out the kickback and then delete the review.
      - akamaozu 4y ago
        An even simpler alternative is to not accept an offer you aren't comfortable with. Two wrongs don't make a right.
  - zionic 4y ago
    - mort96 4y ago
      > First, I purchased a new, highly-reviewed, wifi adapter on Amazon. It didn’t resolve the issue. It did, however, come with an offer for a free 64GB flash drive in exchange for a good reviews. (That was a pretty terrible purchase overall) I read this as clearly making the connection; that of course the product was highly reviewed from people who wanted a free SD card even though the product was garbage. I don't see a reason to assume OP was oblivious, it's just a slightly humorous paragraph.
BruiseLee 4y ago
I have a company-issued laptop with some corporate spyware installed. I'm not actually required to use it for development, so I don't use it. But I have to switch it on from time to time or else I get a nice email from IT. Anyway whenever I switch it on my wifi goes to shit. Apparently it does some SSID scanning every 5 seconds and then keeps sending the scan result to the "mothership". So I switch it on once or twice a week for an hour or so to do its spying thing.
- m463 4y ago
  > or else I get a nice email from IT. what would it say? how ridiculous. I'll bet you can't insert USB flash drives either.
  - tenacious_tuna 4y ago
    probably something like "hey, it looks like updates haven't been installed on your corporate laptop in the last three months. Please fix that or we're going to ban it from our systems."
  - tfigment 4y ago
    My company "allows" USB sticks but they will encrypt any files on it with key tied to that machine. Had a tech updated a config file when after this was silently rolled out and poof line down for the day as it couldnt be used to reimage systems on the embedded pcs.
    - deleted 4y ago
      [deleted]
  - paranoidrobot 4y ago
    We have to have endpoint monitoring software on all employee computers for SOC2. We keep the monitoring to as minimal as needed to meet that requirement. If your workstation stops checking in, or tells us your workstation doesn't comply then we will ping you to fix it. It's always polite: Your machine is reporting X please fix that. E: I should point out that our monitoring doesn't involve wifi like the person you replied to.
noncoml 4y ago
My MacBook Pro(x86) takes 10ms to ping the Asus router. Any other router, 1-2ms. Windows takes 1-2ms for the same ASUS router.
- Nextgrid 4y ago
  Is it consistent? It's still not good and I'd be curious about the explanation, but at least if it's consistent with no packet loss it shouldn't cause any issues.
dav43 4y ago
Imagine trying to debug this on an iPad. /s
- deleted 4y ago
  [deleted]
martyvis 4y ago
Why on earth would a paint program need to be interested in WiFi roaming? I can understand that Qt might have network management functions, and even that a paint program might want to check for updates or licensing via the Internet, but it does seem bizarre that they would chain through to something that enumerates through interfaces like that.
- brigade 4y ago
  It's not; Qt helpfully started the polling automatically when a QNetworkAccessManager was instantiated. Which is needed for network access via Qt, such as fetching ads for the free version.
Szpadel 4y ago
I had issue that sometimes whole home network had lags multiple seconds long. I noticed strange activity on all leds on ISP router/modem, Wireshark session found that NX no machine player was flooding broadcasts for local network machines discovery and apparently router tried to forward all those broadcasts to all connected devices in the network, what wouldn't be that bad, until there is some device with weak wifi connection that cannot receive them fast enough. some queue on the router filled up, and router stopped routing anything untill it delivered some of those broadcasts to everyone
throwaway09223 4y ago
I think I encountered a similar issue on android. The Alibaba app was enumerating the wireless devices periodically and causing my bluetooth headphones to de-sync. I didn't dig too far into it beyond verifying that uninstalling Alibaba fixed the problem. But it's super obnoxious that userspace apps are given handles on enough of the wireless stack such that they can break things.
Groxx 4y ago
My favorite WiFi issue: USB-3 produces 2.4GHZ noise and can disrupt WiFi, and I had a USB-3 hub plugged in much of the time to get some extra ports on my laptop: https://www.pcmag.com/opinions/wireless-witch-the-truth-about-usb-30-and-wi-fi-interference https://www.pcmag.com/opinions/wireless-witch-the-truth-abou... So now I pretty much exclusively buy USB-2 hubs. Very little saturates 2.0 speed anyway.
- oynqr 4y ago
  Bonus points for USB 3.0 wifi dongles that jam themselves.
- ReactiveJelly 4y ago
  Used to have a USB 3 device that would jam an RF keyboard if it was between the keyboard and the adapter...
hericium 4y ago
Not the same but apparently quite similar: Apple Maps location scan spikes WiFi latency every 60 seconds[1] [1] https://news.ycombinator.com/item?id=31356730 https://news.ycombinator.com/item?id=31356730
orliesaurus 4y ago
This reminds of me that I have an Ubuntu machine which connects to the WiFi and crashes the router. The worst part is that I have no clue what causes it and no clue how I would even get started analyzing why the router crashes...seconds after the Ubuntu machine connects to the network, via WiFi. I just gave up connecting to that network altogether. It works fine if I use it on other networks. lol
Springtime 4y ago
Years ago I experienced an issue with a Cyberpower UPS software update that interfered with the system's Bluetooth, causing devices to not be able to connect, inexplicably since the software doesn't use BT for anything. Only after much online searching did I stumble on another user with the same issue and after uninstalling it and reverting to an earlier version the issue immediately went away. I've since kept a more open mind as to what may be causing network issues.
pR0Ps 4y ago
This has been an issue forever (I have a similar blog post from 4+ years ago tracking down the exact same issue: https://cmetcalfe.ca/blog/diagnosing-periodic-high-ping-times-on-macos.html https://cmetcalfe.ca/blog/diagnosing-periodic-high-ping-time... ) and I can't believe it's still not fixed.
- armada651 4y ago
  It is fixed, but it requires Qt application developers to update their application to Qt6 or as a workaround they can disable bearer management in Qt5.
bykattthrow 4y ago
recalls me of the time where at office the LCD screens would sometimes turn off, at seemingly random locations. it took a long time for people to realise movement caused it, then further time to discover it was when the chair would pump when they stood up.
armada651 4y ago
The amount of hours wasted by this Qt bug is immeasurable. I'm one of the commenters on the issue 5 years ago and still people are being plagued by it. Qt should've posted a public advisory announcement when this was discovered. Instead it has plagued users for nearly a decade now because very few Qt developers even know that their Qt5 apps are ruining the WiFi connections of their users.
- rob_c 4y ago
  Would be nice if a major distro mitigated against this publicly. Why addressing this took so long I think it's worth taking a step back to look into. This isn't some small UI change it impacts system performance in a negative way for so many users.
  - armada651 4y ago
    I think the reason that it took so long is because it was actually working by design. The only reason it got fixed is because Qt6 removed the offending feature completely. The source of the problem is Bearer Management which was a feature of Qt5 where it occasionally polls the OS for WiFi networks to speed up WiFi roaming: https://doc.qt.io/qt-5/bearer-management.html#roaming https://doc.qt.io/qt-5/bearer-management.html#roaming However the result of those polling requests is that the OS might opt to drop everything else to complete the network scan. Some incomplete workarounds were implemented that mainly revolved around disabling the feature on affected systems: https://codereview.qt-project.org/c/qt/qtbase/+/214029 https://codereview.qt-project.org/c/qt/qtbase/+/214029
    - rob_c 4y ago
      > working by design Without reopening old wounds and _days_ of wasted dev effort. Defective design is still a bug.
T3RMINATED 4y ago

594 points by emidoots 4y ago

deleted 4y ago

[deleted]

zdw 4y ago

My most unusual wifi issue was on a system that said it had a great connection (SNR) and was running at high speed, but would just not pass traffic if it was further than about 1m from a base station. Turned out to have multiple antennas, and the transmit antenna was broken, so it could receive just fine, but not transmit over anything but short distances. Sometimes the physical layer is the problem, even if the logical layer says everything is fine.

klysm 4y ago
I guess the logic layer only said the receive side was fine. It can’t see what’s happening within the transmit antenna I don’t think
- Nextgrid 4y ago
  I'm surprised there isn't a mechanism for the link peer to report the SNR to the sender from its perspective. I've had the same issue without any antenna troubles - Mac would constantly connect to the 5GHz network and struggle to send any packets out, yet the displayed signal strength was good. It turns out it was able to "hear" the AP just fine, but the AP had trouble hearing back, yet somehow there's no feedback mechanism for it to know.
  - klysm 4y ago
    A kind of SNR ping seems like it would make a lot of sense. I don’t know enough about radios but anybody know why that doesn’t exist?
    - sbierwagen 4y ago
      Wifi 6 has all sorts of active sensing stuff for spatial frequency reuse, but GP didn't say what generation of wifi equipment was being used.
    - ac29 4y ago
      The industrial (non-wifi) radios I use at work have a signal/noise ping function. Its very useful.

zionic 4y ago

Wow. This should be the kind of thing windows/your OS detects and warns you about.

unnouinceput 4y ago
Why? Since when your OS knows what you want to do? Maybe I do intent to enumerate wifi's around me every 10 seconds, so why would OS would be bothered to do such warning? Also Windows has event viewer, you can see there what's going on anyway (consider that the OS warning you want)

jtchang 4y ago

I believe this can happen on macos as well.

LaputanMachine 4y ago
In macOS there are also ping spikes when you open the WiFi menu bar [1]. This still happens in macOS Monterey. [1]: https://developer.apple.com/forums/thread/97805 https://developer.apple.com/forums/thread/97805
- walrus01 4y ago
  If I had to guess it's because the system is temporarily pausing tdd wifi traffic while it scans the 2.4 and 5.x GHz bands to see what SSIDs are broadcasting. It is a bit of a trade off since if you want to see every possible available AP, even the shitty ones with signal levels at like -80, you can't be noisy on your own radio at the same time as you scan the band. Remember it's a half duplex medium. It does it even more if you hold down option and click the wifi menu bar, to get detailed signal strength/info on the AP you're presently connected to.
- nicoburns 4y ago
  This seems more reasonable, given that: 1. I can't see how you'd enumerate wifi networks without degrading network performance. 2. The user has specifically initiated a wifi-related action. 3. There's not generally any need to use that menu unless the network is already not working.
icedchai 4y ago
I've seen this happen on my Mac desktop. I eventually found a post where someone mentioned turning off "find my mac" fixing it: https://developer.apple.com/forums/thread/97805?page=2 https://developer.apple.com/forums/thread/97805?page=2

deleted 4y ago

[deleted]

naikrovek 4y ago

I don't think I would have ever figured this out, if it happened to me. the very first thing I do when I have a problem on wifi, is to remove wifi from the equation. wired Ethernet is so much better, and so far, the problem always disappears.

massysett 4y ago
I had this exact same problem with Citrix Workspace. I tried disabling Wi-Fi scanning but had mixed results with that for some reason. Now I have bought a cheap Wi-Fi extender for maybe $30 and plugged my desktop’s Ethernet jack into it. So far this is working extremely well. I disabled the other Wi-Fi extending features of the extender, so essentially it’s a huge Wi-Fi to Ethernet dongle. I find it stupid that I have to employ such a janky solution to this. Citrix Workspace on the Mac does not have this problem, but using an old MacBook Pro for this was undesirable for various reasons.

AnotherGoodName 4y ago

Anyone ever had arp storms on a home network? I've had something trigger every device into asking 'who has xyz ip tell [Mac]'. It made the network unusable and even rebooting systems it would come back since as soon as one device asked the question (sent the broken arp packet) all other devices decided they too needed to know. The solution that worked was to flip the circuit breaker for the whole house and reset every network device at once.

klysm 4y ago
I haven’t had a problem where rebooting the house has fixed it thankfully
- somat 4y ago
  I laughed, but it made me think, with "smart" houses becoming a thing, this will one day become a common occurrence. sigh
mh- 4y ago
Yes, generated by AT&T's wireless STBs (cable boxes) back around 2014-15. It was a nightmare to figure out, as I recall.
dylan604 4y ago
That takes did you turn it off and on again to an entirely different level. What if we need to do this city wide?
- wizofaus 4y ago
  That sounds like a good plot for a movie - the day we had to reboot the entire internet...
  - Lammy 4y ago
    "South Park already did it": https://en.wikipedia.org/wiki/Over_Logging https://en.wikipedia.org/wiki/Over_Logging

chedabob 4y ago

Reminds of the issue on Mac OS where Location Services would cause ping spikes https://news.ycombinator.com/item?id=31356730 https://news.ycombinator.com/item?id=31356730

hbn 4y ago
Here's a spicy meatball for you: wifi lag spikes caused by placing an AirPlay button in the touchbar https://mnpn.github.io/blog/airplay-network-disaster https://mnpn.github.io/blog/airplay-network-disaster Previous discussion: https://news.ycombinator.com/item?id=31706283 https://news.ycombinator.com/item?id=31706283
- m463 4y ago
  I wish I could decisively turn off airplay on macos. It's the source of so many weird issues. For example, locked down mac, using wifi at a friend's house and their LG tv shows up as an airplay mirroring device. Why should my machine be discovering that TV without me asking? When I'm on a public network, I'd like to make my machine output-only, not promiscuous in this way. there was also an issue where a macbook would randomly lose its onboard sound and somehow default to using a nearby appletv as the output device.
  - jabbany 4y ago
    > I'd like to make my machine output-only, not promiscuous in this way. The TV advertises itself on the network so it's the one being promiscuous. Your machine is still being passive, it just shows you the devices that are have advertised themselves. No idea about the sound thing though, I don't use any Mac stuff :)
  - month13 4y ago
    macOS is so frustrating at times, as there's some cool features that are gated by magic, so not only do they not work at times and offer no diagnostic resolutions, also cripple networks. I recall disabling the `awdl` adapter can stop a lot of this behavior, at the cost of breaking these systems. I used to do this when using Moonlight, as it would cause periodic ping spikes.

Fitilii 4y ago

brainzap 4y ago

I hate wifi issues so much, specially when you stream audio.

wizofaus 4y ago
Definitely my biggest bugbear with relying in streaming for music - it's the one thing I use apple hardware for (apple tv) and I can't even sync music to it anymore, plus there's no ability to control buffering that's worked so far. So I'm stuck with listening to music knowing it might stutter at any moment...
Nextgrid 4y ago
The main problem is that OSes do a terrible job at reporting Wi-Fi performance. RSSI is a very poor metric by itself, yet is all that's driving the wireless signal strength indicator. Most wireless links are constantly in a barely working mode that's only made usable by TCP and various retransmission/error-correction algorithms on top, so a lot of connections that people think are "fine" (especially when the signal strength meter is maxed out) are actually not fine at all. There is no magic and those workarounds don't work for real-time streams such as calls/games/etc, so those "fine" connections will crap out miserably as soon as users jump on a call or game. I'm not sure if there's a way for the OS to get any more info about the link quality/stability from the network card itself, but a purely software-level workaround could be to just track all TCP sessions (should be easy, as that's already managed by the kernel), average the percentage of retransmissions across all of them (to prevent a single bad server from skewing the result) and factor that into the "signal strength" meter. An easy way to test this yourself is to run a ping towards your default gateway (the IP of your router). You should see a consistently low latency (in the low single-digits range) and no packet loss. If you're seeing losses or significant variation in response times, your connection is bad and you should do something about it (get closer to the AP or install a second one).

valleyer 4y ago

Nice debugging. Do I understand correctly that the registry reads aren't actually the cause of the problem but rather just a signal that a QNetworkAccessManager is active and causing a scan? If so, is there a better routine to break on in the debugger to see it actually initiating a scan?

muststopmyths 4y ago
You can see a hint in the debugger screenshot. The call is not directly a registry read but to the iphelper API. There are functions in there that enumerate adapters. Knowing nothing about this scanning process, I’m just assuming they first enumerated wireless adapters. So you could start with iphelper and then explore deeper into how you tell the card to scan. There’s probably some API for that as well.
- valleyer 4y ago
  Ah, good point. Wish the backtrace were fully symbolicated (for the system DLLs, at least). Thanks!

yellow_lead 4y ago

> At the exact same time the lag spikes occur, MBPP starts querying the registry keys for all of the network interfaces. Can anyone tell me why this causes the network issue? Don't understand how querying the registry can cause this.

Arnavion 4y ago
Querying the registry does not cause the issue. Querying the registry is a thing that Qt does as part of the code that causes the issue.

proactivesvcs 4y ago

I've got a customer enjoying this exact fault at the moment, what luck.

RicoElectrico 4y ago

The "proper" solution not depending on the application layer: https://www.reddit.com/r/GlobalOffensive/comments/3ahg59/fix_for_wireless_ping_spikes/ https://www.reddit.com/r/GlobalOffensive/comments/3ahg59/fix... Turn autoconfig back on only when you restart your PC or disconnect from the network (maybe someone can automate this by checking connectivity without scanning networks, enabling autoconfig, and then turning it back off)

networkwanderer 4y ago

I love these debugging stories but its a total nightmare to deal with these kinds of issues. At the moment there's this really weird network issue we're having where iPhones are unable to play Netflix on the Wifi. Every other device works fine but iphone 7, 8 (2 devices) and SE can't stream Netflix. I noticed there is other things they can't do, for example the page for the fast.com speedtest loads but the speedtest cant be performed. Same with the Google speedtest. The phones also can't access Apples update server on the wifi. Other network stuff does work fine, youtube works, browsing works, etc. The behaviour is consistent across the iphones and all these things work fine on multiple other devices on the same network. I can't make sense of it at all. Called internet provider and they didnt know either apparently other people had the same issue but nothing has changed from their side of things. Called Apple support and they are putting the blame on the network provider. Tested one of the devices on a different wifi network and works fine. AFAIK if you're an internet router the packets look the same no matter what device is being used so I think this must be some Apple software issue. Or maybe my router is cursed.

mrb 4y ago
I'm fairly confident you are victim of a PMTUD black hole. It's easily fixed by making your router force the TCP MSS to a slightly lower value. All your symptoms are explained by this (some but not all devices are affected, some but not all services are unreachable).
- kalleboo 4y ago
  Yeah, not having an option to set the MTU was the reason I had to stop using the Apple AirPort Extreme when we moved to a new apartment, the symptoms were all the same as GP, limiting the MTU fixed it.
- cryptonector 4y ago
  Or better yet, use packetization PMTUD. 15 years after that was published by the IETF, every device should implement it by default.
  - 4y ago

lobsterboix 4y ago

This is incredible, we use QT5.12 for an embedded device application, and this issue has been a really weird one for us and this spot on resolves it! See browsing HN at work does pay off!

avg_dev 4y ago
Haha, that’s excellent. Your coworkers will be happy I am sure. And I love a good debugging story myself.
rurban 4y ago
We should really upgrade our QT though

deleted 4y ago

[deleted]

josephcsible 4y ago

The "new, highly-reviewed, wifi adapter" pictured in the article looks like Alibaba garbage. I'm surprised it didn't cause some worse problem.

jandrese 4y ago
"Highly Reviewed" and it comes with a "leave a 5 star review for a kickback" offer. A card like that is grounds for returning the thing and leaving a 1 star review IMHO.
- josephcsible 4y ago
  Amazon has made a habit lately of rejecting your review if you do that. It's like they want to help these scammers.
  - Nextgrid 4y ago
    Can you delete reviews? An alternative could be to take them up on the offer, post the review, cash out the kickback and then delete the review.
    - akamaozu 4y ago
      An even simpler alternative is to not accept an offer you aren't comfortable with. Two wrongs don't make a right.
- zionic 4y ago
  - mort96 4y ago
    > First, I purchased a new, highly-reviewed, wifi adapter on Amazon. It didn’t resolve the issue. It did, however, come with an offer for a free 64GB flash drive in exchange for a good reviews. (That was a pretty terrible purchase overall) I read this as clearly making the connection; that of course the product was highly reviewed from people who wanted a free SD card even though the product was garbage. I don't see a reason to assume OP was oblivious, it's just a slightly humorous paragraph.

BruiseLee 4y ago

I have a company-issued laptop with some corporate spyware installed. I'm not actually required to use it for development, so I don't use it. But I have to switch it on from time to time or else I get a nice email from IT. Anyway whenever I switch it on my wifi goes to shit. Apparently it does some SSID scanning every 5 seconds and then keeps sending the scan result to the "mothership". So I switch it on once or twice a week for an hour or so to do its spying thing.

m463 4y ago
> or else I get a nice email from IT. what would it say? how ridiculous. I'll bet you can't insert USB flash drives either.
- tenacious_tuna 4y ago
  probably something like "hey, it looks like updates haven't been installed on your corporate laptop in the last three months. Please fix that or we're going to ban it from our systems."
- tfigment 4y ago
  My company "allows" USB sticks but they will encrypt any files on it with key tied to that machine. Had a tech updated a config file when after this was silently rolled out and poof line down for the day as it couldnt be used to reimage systems on the embedded pcs.
  - deleted 4y ago
    [deleted]
- paranoidrobot 4y ago
  We have to have endpoint monitoring software on all employee computers for SOC2. We keep the monitoring to as minimal as needed to meet that requirement. If your workstation stops checking in, or tells us your workstation doesn't comply then we will ping you to fix it. It's always polite: Your machine is reporting X please fix that. E: I should point out that our monitoring doesn't involve wifi like the person you replied to.

noncoml 4y ago

My MacBook Pro(x86) takes 10ms to ping the Asus router. Any other router, 1-2ms. Windows takes 1-2ms for the same ASUS router.

Nextgrid 4y ago
Is it consistent? It's still not good and I'd be curious about the explanation, but at least if it's consistent with no packet loss it shouldn't cause any issues.

dav43 4y ago

Imagine trying to debug this on an iPad. /s

deleted 4y ago
[deleted]

martyvis 4y ago

Why on earth would a paint program need to be interested in WiFi roaming? I can understand that Qt might have network management functions, and even that a paint program might want to check for updates or licensing via the Internet, but it does seem bizarre that they would chain through to something that enumerates through interfaces like that.

brigade 4y ago
It's not; Qt helpfully started the polling automatically when a QNetworkAccessManager was instantiated. Which is needed for network access via Qt, such as fetching ads for the free version.

Szpadel 4y ago

I had issue that sometimes whole home network had lags multiple seconds long. I noticed strange activity on all leds on ISP router/modem, Wireshark session found that NX no machine player was flooding broadcasts for local network machines discovery and apparently router tried to forward all those broadcasts to all connected devices in the network, what wouldn't be that bad, until there is some device with weak wifi connection that cannot receive them fast enough. some queue on the router filled up, and router stopped routing anything untill it delivered some of those broadcasts to everyone

throwaway09223 4y ago

I think I encountered a similar issue on android. The Alibaba app was enumerating the wireless devices periodically and causing my bluetooth headphones to de-sync. I didn't dig too far into it beyond verifying that uninstalling Alibaba fixed the problem. But it's super obnoxious that userspace apps are given handles on enough of the wireless stack such that they can break things.

Groxx 4y ago

My favorite WiFi issue: USB-3 produces 2.4GHZ noise and can disrupt WiFi, and I had a USB-3 hub plugged in much of the time to get some extra ports on my laptop: https://www.pcmag.com/opinions/wireless-witch-the-truth-about-usb-30-and-wi-fi-interference https://www.pcmag.com/opinions/wireless-witch-the-truth-abou... So now I pretty much exclusively buy USB-2 hubs. Very little saturates 2.0 speed anyway.

oynqr 4y ago
Bonus points for USB 3.0 wifi dongles that jam themselves.
ReactiveJelly 4y ago
Used to have a USB 3 device that would jam an RF keyboard if it was between the keyboard and the adapter...

hericium 4y ago

Not the same but apparently quite similar: Apple Maps location scan spikes WiFi latency every 60 seconds[1] [1] https://news.ycombinator.com/item?id=31356730 https://news.ycombinator.com/item?id=31356730

orliesaurus 4y ago

This reminds of me that I have an Ubuntu machine which connects to the WiFi and crashes the router. The worst part is that I have no clue what causes it and no clue how I would even get started analyzing why the router crashes...seconds after the Ubuntu machine connects to the network, via WiFi. I just gave up connecting to that network altogether. It works fine if I use it on other networks. lol

Springtime 4y ago

Years ago I experienced an issue with a Cyberpower UPS software update that interfered with the system's Bluetooth, causing devices to not be able to connect, inexplicably since the software doesn't use BT for anything. Only after much online searching did I stumble on another user with the same issue and after uninstalling it and reverting to an earlier version the issue immediately went away. I've since kept a more open mind as to what may be causing network issues.

pR0Ps 4y ago

This has been an issue forever (I have a similar blog post from 4+ years ago tracking down the exact same issue: https://cmetcalfe.ca/blog/diagnosing-periodic-high-ping-times-on-macos.html https://cmetcalfe.ca/blog/diagnosing-periodic-high-ping-time... ) and I can't believe it's still not fixed.

armada651 4y ago
It is fixed, but it requires Qt application developers to update their application to Qt6 or as a workaround they can disable bearer management in Qt5.

bykattthrow 4y ago

recalls me of the time where at office the LCD screens would sometimes turn off, at seemingly random locations. it took a long time for people to realise movement caused it, then further time to discover it was when the chair would pump when they stood up.

armada651 4y ago

The amount of hours wasted by this Qt bug is immeasurable. I'm one of the commenters on the issue 5 years ago and still people are being plagued by it. Qt should've posted a public advisory announcement when this was discovered. Instead it has plagued users for nearly a decade now because very few Qt developers even know that their Qt5 apps are ruining the WiFi connections of their users.

rob_c 4y ago
Would be nice if a major distro mitigated against this publicly. Why addressing this took so long I think it's worth taking a step back to look into. This isn't some small UI change it impacts system performance in a negative way for so many users.
- armada651 4y ago
  I think the reason that it took so long is because it was actually working by design. The only reason it got fixed is because Qt6 removed the offending feature completely. The source of the problem is Bearer Management which was a feature of Qt5 where it occasionally polls the OS for WiFi networks to speed up WiFi roaming: https://doc.qt.io/qt-5/bearer-management.html#roaming https://doc.qt.io/qt-5/bearer-management.html#roaming However the result of those polling requests is that the OS might opt to drop everything else to complete the network scan. Some incomplete workarounds were implemented that mainly revolved around disabling the feature on affected systems: https://codereview.qt-project.org/c/qt/qtbase/+/214029 https://codereview.qt-project.org/c/qt/qtbase/+/214029
  - rob_c 4y ago
    > working by design Without reopening old wounds and _days_ of wasted dev effort. Defective design is still a bug.

T3RMINATED 4y ago