Minecraft wiki entry for Server_maintenance, associated text: If you want to ban a player from playing on your server, edit the minecraft\banned-ips.json", where "minecraft" is the folder where minecraft was installed on the server and add the user you want to ban to this banned-ips.json file. To ban an IP address from the server, the full IP address must be specified; wildcards are not valid. Players who are banned through this method will see "Your IP address is banned from this server!" when attempting to connect. Alternatively, an operator can use the "ban-ip" command via "/ban-ip ipaddress", where "ipaddress" is the IP address of the user you wish to ban. This can be undone via the operator issuing the "pardon-ip ipaddress" command or editing the server's banned-ips.json file.