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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.

Thanks

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2 Answers 2

up vote 7 down vote accepted

When you create a MySQL user username@example.com MySQL has to do a reverse lookup on every IP address connecting to it to determine whether they are part of example.com.

Of course, there's no restriction on creating reverse lookups, so I can quite happily ask my provider to set the reverse lookup for my IP address to be google.com if I want... or example.com if I happen to know that's what the users in your database have. This won't let me in, as MySQL then does a forward lookup on the returned domain to make sure it matches the same IP address that's connecting.

You can switch this off with skip_name_resolve in your my.cnf. There are many good reasons for doing this.

The reason you are getting this error is that the IP address in question has no reverse lookup at all.

You also have malicious attackers from China trying to brute force their way into your database. That should be your top priority.

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I think it's a verry verry bad Idea to expose your database servers directly on the internet

If you are replicating to a remote host and need internet access to achive that, i suggest you setup a vpn between the two networks and bind you mysql servers to listen only to the local network.

If both of your hosts are on the same local network, you will be safe to bind your mysql servers to that network

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