域名系统（英文：Domain Name System，缩写：DNS）是互联网的一项服务。它作为将域名和IP地址相互映射的一个分布式数据，能够使人更方便地访问互联网。DNS使用TCP和UDP端口53。我们平时上网都默认使用到了，只是它自动完成罢了。
下面介绍2020年表现最佳的15项免费DNS服务器。
| DNS Provider Name | Primary DNS Server | Secondary DNS Server |
|---|---|---|
| 8.8.8.8 | 8.8.4.4 | |
| OpenDNS Home | 208.67.222.222 | 208.67.220.220 |
| CloudFlare | 1.1.1.1 | 1.0.0.1 |
| Quad9 | 9.9.9.9 | 149.112.112.112 |
| Level3 | 209.244.0.3 | 209.244.0.4 |
| Verisign | 64.6.64.6 | 64.6.65.6 |
| DNS.WATCH | 84.200.69.80 | 84.200.70.40 |
| Comodo Secure DNS | 8.26.56.26 | 8.20.247.20 |
| Norton ConnectSafe | 199.85.126.10 | 199.85.127.10 |
| GreenTeamDNS | 81.218.119.11 | 209.88.198.133 |
| SafeDNS | 195.46.39.39 | 195.46.39.40 |
| OpenNIC | 23.94.60.240 | 128.52.130.209 |
| SmartViper | 208.76.50.50 | 208.76.51.51 |
| Dyn | 216.146.35.35 | 216.146.36.36 |
| FreeDNS | 37.235.1.174 | 37.235.1.177 |
| Alternate DNS | 198.101.242.72 | 23.253.163.53 |
| Yandex.DNS | 77.88.8.8 | 77.88.8.1 |
| UncensoredDNS | 91.239.100.100 | 89.233.43.71 |
| Hurricane Electric | 74.82.42.42 | |
| puntCAT | 109.69.8.51 |
下面再附上几张效率对比图。
