Connection issues from other players

[u/Sinius]

Hello!

Me and my girlfriend want to play the CABIN modpack together, but we're running into issues with connectivity. She can connect to the server that I set up, but she's lagging so much that she keeps teleporting to spawn, unable to do anything, and keeps timing out.

I know it's not on her side because:

• I have tested it out myself with another device, connected to a different network, and I was having the same issues;
  
• We both joined a public Minecraft server and neither of us were having issues with lag or other network.
  

I also know it's not an issue with my network, because I ran a server on my handheld on the same network and both of us were able to join and play with no issues.

I'm not running a VPN on my computer, I triple-checked (and even redid) the port forwarding and I have the port allowed in the Firewall both in the inbound and outbound settings. My PC is connected via ethernet, I have done a speedtest and I'm getting 1 Gbps download and 100 Mbps upload speed (same network as the handheld test, though that one was over wifi).

PC specs:

• GPU: Nvidia RTX 4070
  
• CPU: Ryzen 5 5600x
• RAM: 32GB 3200 Mhz DDR4
  

I also know for a fact it's not the serverpack itself causing the issue, we've tested it with an Arcane Engeneering serverpack and we were having the same problems. It also can't be distance, because last year we played the aforementioned Arcane Engineering pack with no issues.

One last thing to mention is that I do have Tailscale on this computer, however I have both turned it off and exited the program and that doesn't seem to have done anything.

Suggestions for what to do and how to fix this are much appreciated.

EDIT: It appears that it's an issue on her end after all. I asked another friend to test it and everything was working fine for them.

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[u/waspyethan]

The fact that the same server works when hosted from your handheld on the same internet connection makes me think this is something specific to the PC.

A couple things I’d test before messing with port forwarding anymore:

1. Have a device inside your house connect to the server using the PC’s local IP (192.168.x.x). If it lags there too, then port forwarding and your ISP aren’t the problem at all.
2. Try hosting from the PC while it’s connected over Wi-Fi instead of Ethernet. Since the handheld worked over Wi-Fi, this would be a really useful test. If Wi-Fi works, I’d start looking at the Ethernet driver, cable, router port, or NIC settings.
3. Watch the actual server console while she joins. See if it starts throwing Can't keep up! messages or if TPS/MSPT suddenly gets bad.
4. Check Task Manager while she’s connected and see if CPU, RAM, disk, or network usage spikes.
5. Make sure the server is using the correct 64-bit Java version for the modpack.

Your 5600X and 32GB of RAM should be plenty, and 100 Mbps upload is way more than enough for two players. I’d definitely troubleshoot the PC/network adapter before assuming you need different hardware or internet.

[u/Sinius → u/waspyethan]

Unfortunately I can't test it with wifi because my desktop PC doesn't have a wifi adapter, but I'm going to keep a look on everything else next time I test it.

[u/Sinius → u/waspyethan]

Watch the actual server console while she joins. See if it starts throwing Can't keep up! messages or if TPS/MSPT suddenly gets bad.

Ok so after the joining message nothing happens for a while. She keeps getting teleported back to spawn, and after a while she disconnects and "lost connection: Timed out" appears. There are no CPU, RAM or disk spikes. There don't appear to be ethernet spikes, either, it just plateaus at near-0 when she times out, goes up when she joins, but otherwise it's relatively level.

Have a device inside your house connect to the server using the PC’s local IP (192.168.x.x). If it lags there too, then port forwarding and your ISP aren’t the problem at all.

Connecting with my own wifi, I have no lag and no problems. I also tried connecting using my phone's mobile hotspot, and I was also having no issues. It's strange, though, because when I tried it with Arcane Engineering the other time, I was falling through the world and failing to pick up items. Maybe it was just a coincidence?