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Overview

We've been playing together with friends on a server I host for a week or so now, since I'm running the server 24-0 people started noticing that whenever I connect to it, they'll instantly start noticing very bad connection problems, however I wasn't experiencing that, since I'm connected locally. The moment I disconnect, the issue stops, and everyone goes back to having good connection. This made me curious to why this happens, so I started monitoring the network traffic of the server PC and turns out they're correct.

The server when I'm not on:

send data: 448Kbps, receive data: 32Kbps

The server when I'm on:

send data: 10.7Mbps, receive data: 912Kbps

I just couldn't find why this is happening. I got Wireshark and started monitoring what really happens. It's basically a billion packets with [ACK] and [PSH,ACK] tags, using TCP (the data itself is encrypted).

The worst part is, that I increase everyone else's internet use with this, because clients communicate between each other too, so the images you see there, the big network spike happens to all my friends too, when I'm on the server. It's like my Minecraft wants to DDOS everyone.

So I assume two things.:

  1. There's a network loop somewhere and I don't know where or how could I find that.
  2. Since I'm connecting locally, the server detects low latency and thinks it's ok to update everything about my connection every nanosecond, and just floods the router with packets, choking everyone else out.

I couldn't find any solution to that, not even this happening to anyone else, so I'm turning to this forum. If you have any idea why this could be happening, please help.


Specifications

The server is running on a completely different PC on my local network and is connected to the same router as my client PC. The server has a static IP address.

  • Server: FTB direwolf20 modpack(v 1.10.1)
    • RAM: 24GB (18 utilized)
    • Processor: Intel i5 6600
  • Internet Connection
    • Download Speed: 500mbps
    • Upload Speed: 20mbps
  • Minecraft Version: 1.16.5
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  • Have you tried connecting from your public IP? That might fix the problem if its your second theory
    – c1uq92
    Aug 9, 2021 at 14:40
  • My router forbids going out to the internet, if I want to connect to something on my local network. That being said. I did try to use VPN to bypass that, and connected to the public IP, the issue was the same. And the network traffic went way up again.
    – Guest
    Aug 9, 2021 at 15:32
  • Welp, that's all I can tell you lol. I haven't really dipped my feet into too much networking, but I'm sure there are other people here who can help :\
    – c1uq92
    Aug 9, 2021 at 23:44
  • 1
    Do you run any mods or funky resource packs? Xray etc will massively increase amount of data being sent.
    – SF.
    Aug 10, 2021 at 2:54
  • Other than Optifine, I wasn't running anything. The mods were exactly the same as everyone else's. We did install 2 mods on top of the base direwolf20 modpack, that being Origins and Immersive Portals. But since everyone else is using those too, I assume they cannot be the issue, because the server only starts flooding packets when I join. I did try reinstalling the modpack completely, deleting optifine too with it, at first it didn't solve it, I was still making others lag, then it seemed like it got better a bit. though it's still way higher than compared to others' network traffic.
    – Guest
    Aug 10, 2021 at 7:24

1 Answer 1

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I found out what the issue was. It was me using a custom datapack race for the Origins mod.

For people who might end up in this thread in the future because of high network traffic with minecraft:

For diagnostics, I used Wireshark, and NetLimiter 4.0, but any programs should do that are able to monitor your network/packet traffic.

I suggest you try to isolate the issue as much as possible. For me, I knew the issue was with me, because the network traffic only spiked when I joined, not when others.

I ran a barebone minecraft server on the same version as the modpack (for me 1.16.5) to see if the issue was related to the modpack, or if it occurs in vanilla minecraft too, thus further isolating the problem. It was only with the modpack. After this it clicked, that the issue could be with my custom race that I added to the Origins mod, but if your case is different, or for any reason doesn't apply here, the next step I'd do is temporarily moving my player file out of the server, so when you join back into the game, the server generates a completely new player file for you. This is useful, because your previous player file might be "corrupted" by mods, or just bugs in general, just so it doesn't crash the game, but it creates large amounts of traffic. (keep in mind, this resets everything about your in game character, things like your inventory, level will be deleted.)

As previously mentioned in the comments by the user SF. Xrays, or other cheats massively increase the amount of network traffic. So if you use anything like those, I'd suggest trying to disable them first.

Hope this helps anyone else, having similar problems in the future! :)

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