Internet connection becomes unstable when using qBittorrent

[mojo-jojo-7]

qBittorrent & operating system versions

qBittorrent: 4.5.2 x64 Operating system: Windows 10 Pro 21H2 10.0.19044 Qt: 5.15.8

What is the problem?

When qBittorrent is running, internet connection becomes unstable system-wide. It takes a couple of minutes and then webpages just give the "This site can’t be reached" page like there's no internet. While this is happening, qBittorrent seems to continue doing whatever it's doing without issues but eventually my VPN disconnects itself and gets stuck on "Waiting for usable network to connect" loading page (and qBittorrent, of course, loses the connection as well after this). Sometimes, I leave qBittorrent running overnight and I observed that it doesn't disconnect my VPN and the torrents keep running, but websites still don't load.

Steps to reproduce

No response

Additional context

I understand this is super random, probably not reproducible for debugging and that it could have something to do with my setup as well, so I'm going to provide more info on this.

• I'm using Proton VPN with qBittorrent bound to its network interface
• I have less than 50 torrents running, most of which have been stale for a long time
• Closing qBittorrent and reconnecting the VPN fixes the internet but it doesn't take long for this to repeat after starting qBittorrent client back

Would really appreciate help identifying the issue here!

Log(s) & preferences file(s)

No response

[mojo-jojo-7]

One more thing that could be relevant

This has been happening since fairly recently, I'm not quite sure exactly when, but I think it's since v4.5.1. Before that, sometimes the internet would get unstable, as if packets are getting dropped, but I was still largely able to connect. This is what used to happen then:

• Sometimes webpages wouldn't respond, but refreshing the page would fix that
• A scraping program I run used to have some failed downloads citing this error: "ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine"

I am certain that this behavior only occurred while qBittorrent is running

[wrohrb]

I have been having the same issue. Not totally sure if it is a defective network adapter or just qbitorrent, but I would gravitate towards it probably being qbittorrent. It only ever happen with the latest version of qbitorrent when I am downloading many things at once.

I start about a dozen downloads, and my internet connection inevitably drops system wide. I may be able to test with another motherboard later today to see if I can get the same behavior. I will get back to this thread if I can reproduce the error.

Edit:

I don't have time to test it on another computer until later today, but I notice in older versions qbittorrent would only juggle 3 downloads at once, and with this older version the connection never dropped from my system. Maybe the issue lies in the change from juggling only three downloads to juggling more than half a dozen at a time? I have no idea, just throwing that out there.

[mojo-jojo-7]

Is it possible that qBittorrent is somehow filling all the network connections Windows can concurrently make? I don't know the maximum number, but there does seem to be a limit on that.

@wrohrb this would support your observation because more active torrents would make more network connections. I have no idea though, just thinking out loud here

[sage-RJ]

Are you sure you’re not saturating your bandwidth? Your upload and download “speed limits” should be no more than 80% or your throughput as measured on speedtest.net for example.

[mojo-jojo-7]

@sage-RJ I don't enforce any speed limits in qBittorrent, but I'm certain it's not because my bandwidth is full. Because the behavior I described happens regardless of the upload/download activity that's happening in qBit. My internet is not bad either, it's high speed and very stable.

[wrohrb]

Are qBittorrent connection related settings default? Does it make a difference if you disable DHT and only allow TCP? Are you using Wi-Fi or Mobile internet? What network devices to you use? Can you try using different internet provider?

I did test on a second computer and couldn't reproduce the issue, though I only tested for about 10 minutes. It might be an issue with the drivers on my specific NIC. My motherboard has a "Marvell® AQtion AQC113CS 10Gb Ethernet". My internet speed is 500Mb/s fiber. I cannot use a different internet provider, and all of my qbittorrent settings are default.

Again, I am not totally sure if it is something wrong with my computer, or if it is an issue with the application. All I know is that my internet connection only drops when using that specific application and with many torrents going at once.

Update: I tried your suggestion of switching to TCP only and it seemed to completely fix it. I had over 20 torrents going at once for about 30 minutes and no connection issues whatsoever.

[darkMatterSound]

I've been having this issue every time I connect to qbit too and it's been driving me nuts! My internet works fine when connected through my VPN, but as soon as I open qbit, it becomes unstable. I just unchecked "Enable DHT" and that does seem to fix it, so thank you for this solution!

One question though, does this make a noticeable difference in how many search results you get? I'd hate to have this cut down the amount of connections and the cut down my download speed.

Thanks for the help!