I have port 3306 blocked to external connections on Centos server, 3306 is open to a VPN only. I can confirm this using a port check.
But the Maria DB logs has lots of entries for DNS reverse look ups, so what is going on? The lookups aren't even that frequent so doesn't look like a brute force attempt.
Previous similar questions say to block the port but as this is already done am I missing something or is this nothing to worry about?
201211 6:38:38 [Warning] IP address '162.118.5.96' has been resolved to the host name '162.118.5.96.nwinternet.com', which resembles IPv4-address itself.
201211 16:57:22 [Warning] IP address '111.39.122.165' could not be resolved: Name or service not known
201211 16:59:38 [Warning] IP address '170.130.187.30' could not be resolved: Name or service not known
201211 21:46:03 [Warning] IP address '210.26.48.8' could not be resolved: Name or service not known
201212 11:03:35 [Warning] IP address '222.187.223.46' could not be resolved: Name or service not known
201212 16:56:15 [Warning] IP address '194.113.164.121' could not be resolved: Name or service not known
201212 20:47:09 [Warning] IP address '152.32.186.214' could not be resolved: Name or service not known
201212 22:25:32 [Warning] IP address '111.67.195.5' could not be resolved: Name or service not known
201213 1:55:14 [Warning] IP address '106.55.148.26' could not be resolved: Name or service not known
201213 2:17:48 [Warning] IP address '222.223.212.78' could not be resolved: Name or service not known
201213 13:21:20 [Warning] IP address '176.111.173.38' could not be resolved: Name or service not known
201213 18:41:24 [Warning] IP address '59.57.14.138' could not be resolved: Name or service not known
201213 20:11:21 [Warning] IP address '159.89.143.183' could not be resolved: Name or service not known
201214 2:55:37 [Warning] IP address '81.69.57.68' could not be resolved: Name or service not known
201214 6:00:45 [Warning] IP address '185.217.1.114' could not be resolved: Name or service not known
201214 11:55:44 [Note] Hostname 'server-185-153-199-76.cloudedic.net' does not resolve to '185.153.199.76'.
201214 11:55:44 [Note] Hostname 'server-185-153-199-76.cloudedic.net' has the following IP addresses:
201214 11:55:44 [Note] - 185.153.198.99
201214 23:58:44 [Warning] IP address '117.187.141.251' could not be resolved: Name or service not known
201215 4:42:12 [Warning] IP address '219.89.196.131' could not be resolved: Name or service not known
201215 18:26:12 [Note] Hostname '683b217.rederatural.com' does not resolve to '104.140.188.6'.
201215 18:26:12 [Note] Hostname '683b217.rederatural.com' has the following IP addresses:
201215 18:26:12 [Note] - 212.32.237.90
201215 20:27:16 [Warning] IP address '104.196.99.211' has been resolved to the host name '211.99.196.104.bc.googleusercontent.com', which resembles IPv4-address itself.
201216 17:34:39 [Note] Hostname 'c5486.rederatural.com' does not resolve to '104.140.188.46'.
201216 17:34:39 [Note] Hostname 'c5486.rederatural.com' has the following IP addresses:
201216 17:34:39 [Note] - 212.32.237.92
