In Singleplayer there is a function called "Open to LAN". Minecraft (in the serverlist) binds a UDP port and listens for connections to 224.0.2.60:4445 (Yes, that is the actual IP, no matter in what network you are or what your local IP Address is). If you click on "Open to LAN" Minecraft sends a packet every 1.5 seconds to the address: [MOTD]motd[/MOTD][AD]port[/AD]. Minecraft seems to check for the following Strings: [MOTD], [/MOTD], [AD], [/AD]. Anything you write outside of each of the tags will be ignored. Color codes may be used in the MOTD. Between [AD] and [/AD] is the servers port. If it is not numeric, 25565 will be used. If it is out of range, an error is being displayed when trying to connect. The IP Address is the same as the senders one. The string is encoded with UTF-8.