Minecraft wiki entry for Setting_up_a_server, associated text: The default configuration on all Windows computers (the home version) and (just about) all (SOHO) routers is to drop or time out the connections. This is called "stealth mode" and you can read more about it on superuser. Here's a brief summary: "The idea is that refusing a connection instead of timing it out will tell an attacker that there actually is a computer on that IP-Address. With the connection attempt timing out, the hope is that the attacker will ignore the computer."