I don't think you'll need a command.
MySQL doesn't care from where in the world a request comes.
If the user is recognized she'll be let in … and allowed to perfom operations according to the user configuration.
But of course your OS, networking hardware (such as routers) and software should be configured for that!
However you can configure the MySQL server to enable/disable networking.
In the latter case the server will only accept clients running on “localhost”
The easiest way to do that is to use MySQLadministrator from http://www.mysql.com.
But try to describe more in detail what is your situation and problem ?