I've got MySQL Master/Slave setup and I've noticed the following warnings in the mysql log files on both servers:
[Warning] IP address 'xxx.xxx.xxx.xxx' could not be resolved: Name or service not known
I've checked and the DNS lookups works fine and most of these IPs are from China.
I planning to limit access on port 3306 on the firewall however could you please help me to understand what they are trying to do. Are they just trying to connect to the MySQL server. Where I can look for some more details.