https://public-dns.info/nameserver/cn.html
https://www.youtube.com/watch?v=o9fJWDoX4nE
https://linuxconfig.org/how-to-configure-static-ip-address-on-ubuntu-18-10-cosmic-cuttlefish-linux
DNS servers | set up a static ip address in Ubuntu
原文：https://www.cnblogs.com/profesor/p/13151709.html