Just in case they are useful. Some of these I never heard of.
| Provider | Primary DNS | Secondary DNS | 
|---|---|---|
| 8.8.8.8 | 8.8.4.4 | |
| Quad9 | 9.9.9.9 | 149.112.112.112 | 
| OpenDNS Home | 208.67.222.222 | 208.67.220.220 | 
| Cloudflare | 1.1.1.1 | 1.0.0.1 | 
| CleanBrowsing | 185.228.168.9 | 185.228.169.9 | 
| Verisign | 64.6.64.6 | 64.6.65.6 | 
| Alternate DNS | 198.101.242.72 | 23.253.163.53 | 
| AdGuard DNS | 176.103.130.130 | 176.103.130.131 | 
| CenturyLink (Level3) | 209.244.0.3 | 209.244.0.4 | 
| DNS.WATCH | 84.200.69.80 | 84.200.70.40 | 
| Comodo Secure DNS | 8.26.56.26 | 8.20.247.20 | 
| GreenTeamDNS | 81.218.119.11 | 209.88.198.133 | 
| SafeDNS | 195.46.39.39 | 195.46.39.40 | 
| OpenNIC | 198.206.14.241 | 172.98.193.42 | 
| SmartViper | 208.76.50.50 | 208.76.51.51 | 
| Dyn | 216.146.35.35 | 216.146.36.36 | 
| FreeDNS | 45.33.97.5 | 37.235.1.177 | 
| 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 | |
| Neustar | 156.154.70.1 | 156.154.71.1 | 
| Fourth Estate | 45.77.165.194 | |
| Tenta | 99.192.182.100 | 99.192.182.101 |