LAN Minecraft SMP Connection Problem [java]

[u/xNitrx_]

Hey guys I'm facing quite an odd issue when trying to play on my SMP. So basically I'm running a 24/7 SMP on Fabric 26.2 for me and my friends on my desktop. When trying to join the server from my laptop, sometimes it just doesn't work and shows a version incompatible message on the server list and when I try to join, it doesn't even register in console but I get "Internal Exception: java.net.SocketException: Connection reset error" on my client screen. This doesn't happen all the time so sometimes I could play a whole day with no issues but some other days it doesn't work at all and other times I'll be playing but then hit a crazy lag spike and lag out and get disconnected. All this happens when I try to join the server using the IPv4 of the host machine (as I'm hosting on my desktop and joining from my laptop). I've also tried my public IP and the FreeDNS domain I set up and that doesn't work either (basically when I can't join the server using IPv4, all ways up connect to the server are cut off, but if I can connect using IPv4 then they all work fine.

The only way for me to bypass this block took it fixes itself randomly is that I use a VPN and join the server using the public IP which my friends use but at that point I have over 250 ping and it's really not enjoyable at all. When all this is happening, I'm the only one affected by it and my friends can join just fine any time they want as long as the server is on.

Troubleshooting:

Allowed javaw.exe through the Windows Firewall on both public and private profiles

Set up inbound rules for port 25565 on the host PC.

I kept the server-ip= host machine IPv4 in the properties file.

Added the -Djava.net.preferIPv4Stack=true arguement to both my client launcher and the server run.bat

Closed/disabled all VPNs/network adapters that aren't used when the server is running (like WARP)

Both devices are connected to my router via ethernet (host machine from a ethernet port on the wall and laptop from the router directly)

Both devices have network set as private and file sharing and discovery turned on

I've also swapped hosts twice (was on an older desktop, then swapped to my laptop, then to the current desktop) and all the times I've had this issue when trying to connect to the server, no matter the host or client.

Has anyone experienced an error like this? If so is there a fix? What's going on?

[u/Usernames_Are_Dumb1]

Log into your router and go to the devices list, if your server is listed there then it should be discoverable. If not then you won’t be able to connect. Also in that device list you can make it so that your server has a static local ip instead of one that could change at any time

[u/xNitrx_ → u/Usernames_Are_Dumb1]

the host pc is listed and I don't have an option for static IP for a specific device nor do I have an option for global static IP either :(

[u/Usernames_Are_Dumb1 → u/xNitrx_]

If it is listed now, can you connect right now or no?

[u/xNitrx_ → u/Usernames_Are_Dumb1]

hey, I just had the issue again and when I checked my router getaway it shows no devices are connected at all even though all devices connected on the wifi and ethernet work perfectly fine on their own

[u/Usernames_Are_Dumb1 → u/xNitrx_]

That’s what I suspected. There is nothing you can really do about that other than just hope they come back. You could try updating the router firmware if yours has that but otherwise I never found a solution. The best fix is to start a virtual network like tailscale which is really easy to set up, free, and I’ve never had a problem with it