Right, and furthermore an address in 3.0.0.0/8 isn't likely to be added on any of your interfaces, so attempting to bind/listen on that will just fail. Even if

Right, and furthermore an address in 3.0.0.0/8 isn't likely to be added on any of your interfaces, so attempting to bind/listen on that will just fail. Even if you add it yourself, there's a tiny chance you might start redirecting some traffic you care about (say, facebook) to a local interface where facebook services are definitely not running. :-P Fortunately, the whole 127.0.0.0/8 block is automatically added to the loopback interface (edit: on Linux at least), so you can bind away to your heart's content.