By default, mysqld blocks a host after 10 connection errors. You can adjust the value by setting max_connect_errors at server startup:

shell> mysqld_safe –max_connect_errors=10000 &
The value can also be set at runtime:

mysql> SET GLOBAL max_connect_errors=10000;
If you get the Host ‘host_name’ is blocked error message for a given host, you should first verify that there is nothing wrong with TCP/IP connections from that host. If you are having network problems, it does you no good to increase the value of the max_connect_errors variable.