我在 Centos 服务器上阻止了 3306 端口的外部连接，3306 端口仅对 VPN 开放。我可以使用端口检查来确认这一点。
但是 Maria DB 日志中有很多 DNS 反向查找条目，那么到底发生了什么？查找频率甚至不是那么频繁，所以看起来不像是暴力破解。
以前类似的问题都说要阻止端口，但是由于这已经完成了，我是否遗漏了什么，或者这没什么可担心的？
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