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I've set up a minecraft server (Vanilla 1.13.2). The server runs fine for local play within my LAN for a long time now but a particular outside connection just won't work.

Please feel free to migrate this to another stackexchange if this is off-topic here, but I'm desperately in need of help.

I want to make the server reachable from the internet.
To do so, I added a port forwarding rule in my router (Port 25565 TCP and UDP) and a firewall exception (allow all inbound and outbound traffic on port 25565).

Now connections work fine for a variety of scenarios:

  • localhost
  • LAN
  • LAN via public IP
  • Internet (same city, same ISP)

However, one friend can't connect to me, despite being able to join another minecraft server.

When logging in, it first seems to work fine (he sees "Downloading Terrain"). However, joining the server is never possible. The connection errors out on a ReadTimeoutException from netty.

I'm completely lost with my troubleshooting here. This is what I already tried and collected information on:

  • java -version is 1.8.0_191-b12
  • OS is Windows 7 x64 behind an AVM Fritz!Box Router
  • Uplink is 5 MBit/s - not particularly fast but should be okay for one client
  • server.properties is standard, with online-mode=true
  • The friend can join another server, also with online-mode=true
    Setting online-mode=false didn't help much - the connection still failed before he could move
  • I reset the router and restarted my PC (= Server) after all changes to network configuration
  • I captured some data transfer in wireshark, but the server IP sends a [FIN, ACK] at some point and then subsequent [RST] This makes me think something on my system must be forcibly closing the established TCP connection, but I can't figure out what it might be since Windows Defender is disabled an I even tried completely disabling Norton AV to no avail.
  • I couldn't get a Hamachi VNet to run at all (not even ping) as an alternative to port forwarding
  • All involved Internet connections are stable
  • canyouseeme.org reports an open port 25565
  • The latency between our computers was consistently about 40ms

The server is started with

java -Xmx6G -Xms6G -jar minecraft_server.1.13.2.jar nogui

And server.properties looks like this:

#Minecraft server properties
#Tue Nov 06 20:30:24 CET 2018
spawn-protection=16
max-tick-time=60000
generator-settings=
force-gamemode=false
allow-nether=true
enforce-whitelist=false
gamemode=0
broadcast-console-to-ops=true
enable-query=false
player-idle-timeout=0
difficulty=1
spawn-monsters=true
op-permission-level=4
pvp=true
snooper-enabled=true
level-type=DEFAULT
hardcore=false
enable-command-block=true
max-players=20
network-compression-threshold=256
resource-pack-sha1=
max-world-size=29999984
server-port=25565
server-ip=
spawn-npcs=true
allow-flight=false
level-name=world
view-distance=32
resource-pack=
spawn-animals=true
white-list=false
generate-structures=true
online-mode=true
max-build-height=256
level-seed=
prevent-proxy-connections=false
motd=Minecraft Server
enable-rcon=false
  • Could I read the script you are starting the server with, or are you running directly? If the latter, could you try to run the server with the nogui parameter? – Manchineel Nov 6 '18 at 20:10
  • @Manchineel I've edited the full command line in as well as dumped the server.properties if that matters. – AlexR Nov 6 '18 at 20:56
  • Any errors thrown in console? (This may help: bugs.mojang.com/browse/MC-34947) – 54D Nov 7 '18 at 13:59
  • @54D I think that‘s the exception but otherwise it just says Downloading Terrain until it disconnects. The server also only logs a timeout. – AlexR Nov 7 '18 at 17:39
  • Upvoted because these weird intermittent ambiguous issues are nightmares and I too would want to get this sorted out chop chop. – Manchineel Nov 7 '18 at 21:25

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