https://blog.wongcw.com/2017/12/04/dnsperf-%e5%be%9e%e5%85%a8%e4%b8%96%e7%95%8c%e5%85%a9%e7%99%be%e5%80%8b%e5%9f%8e%e5%b8%82%e7%9b%a3%e6%b8%ac-dns-%e9%80%9f%e5%ba%a6%e5%92%8c%e5%8f%8d%e6%87%89%e6%99%82%e9%96%93/