Verisign

https://www.verisign.com/en_US/security-services/public-dns/index.xhtml

IPv4 DNS Server:

64.6.64.6

64.6.65.6

IPv6 DNS Server:

2620:74:1b::1:1

2620:74:1c::2:2

Verisign Public DNS is a free DNS service that offers improved DNS stability and security over other alternatives. And, unlike many of the other DNS services out there, Verisign respects your privacy. We will not sell your public DNS data to third parties nor redirect your queries to serve you any ads. See more in the Verisign Public DNS FAQ.