Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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 '' 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.


share|improve this question
up vote 19 down vote accepted

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

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 if I want... or 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.

share|improve this answer

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

If you are replicating to a remote host and need internet access to achieve that, I suggest you setup a VPN between the two networks and bind your 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.

share|improve this answer

When connecting to Mysql remotely, I got an error. I had this warning in /var/log/mysqld.log:

[Warning] IP address 'X.X.X.X' could not be resolved: Temporary failure in name resolution

I just added this line to /etc/hosts file:

X.X.X.X some_name

Problem solved! without using skip-name-resolve, it caused some errors in my local app, when connecting to mysql.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.