The following error show on nagios mysql monitoring status,

Host 'host-name' is blocked because of many connection errors: unblock with 'mysqladmin flush-hosts'

The MySQL max_connect_errors variable to determines  number of succesive interrupted connection requests are allowed after over crossing max_connect_errors that connections are not successful.

To execute the below command flush all cached hosts,
# mysqladmin flush-hosts 

By default, it will blocks a host after 10 connection errors.
mysql > SET GLOBAL max_connect_errors=10000;

if you having any network connection problem, no need to increase the max_connect_error.