openDNS make use of multicast IP addresses to automatically redirect your DNS requests to whichever of their servers is closest to you. They use two public IP addresses of 18.104.22.168 and 22.214.171.124. This simple setup means you don’t have to worry about finding out which of their servers is closest to you or updating your DNS settings when openDNS move their servers or take some servers down for maintenance.
While openDNS can return both the IPv4 and IPv6 addresses relating to a domain, they cannot be queried via IPv6 at the moment. Aside from listening on the standard port 53, their resolvers also listen on port 5353. This is useful if your ISP blocks port 53 to force you to use their DNS servers but aren’t blocking port 53.
For the quickest and most reliable DNS setup, you’ll want to set your ISPs DNS server to be the primary and then openDNS as secondary. Since your ISP will generally answer queries much quicker than openDNS since you’re so close to their servers. While openDNS provide the best reliability by spreading multiple servers around the world.