Minecraft server and IPv6
I was having trouble starting a Minecraft server in Ubuntu Natty. I could connect locally, but my friend couldn't connect over the internet.
I used the standard command to start the server.
$ java -Xmx1024M -Xms1024M \ -jar minecraft_server.jar nogui
I noticed that the server was listening on an IPv6 address. My local network and internet connection is IPv4-only, so my friend would obviously be unable to connect.
$ netstat -an | grep 25565 tcp6 0 0 :::25565 :::* LISTEN
The solution was to pass a property to Java telling it to bind to an IPv4 address.
$ java -Xmx1024M -Xms1024M -Djava.net.preferIPv4Stack=true \ -jar minecraft_server.jar nogui
With that option the server will listen on an IPv4 address.
$ netstat -an | grep 25565 tcp 0 0 0.0.0.0:25565 0.0.0.0:* LISTEN