In a small environment, there's very little reason to rely on DNS resolution inside MySQL. You can disable it by adding skip-name-resolve to your my.cnf or by using the --skip-name-resolve command line argument.
Remember that if you disable DNS lookups, you will need to set permissions using IP addresses rather than host names!
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https://github.com/chaoslawful/zfor
Isn't specifying the permissions by IP the real optimization? Ie. do that and you couldn't care less about DNS settings?
[...] Shared MySQL: Disable DNS Lookups. [...]