openDNS public resolvers use BIND to answer DNS queries, listening on 184.108.40.206 and 220.127.116.11. Aside from answering requests on port 53, their servers also listen on the non-standard port 5353 for users whose ISP aggressively block third party DNS servers.
You may be thinking that since there’s only 2 IP addresses, openDNS only operate 2 servers. Those IP addresses are actually anycast IPs which magically redirect your requests to which server is physically closest to you. This means that they can point your computer in the direction of whichever server could best serve it without you having to work out for yourself which of the opendns servers are closest to you.
There’s some controversy over openDNS blocking system which abuses the NXDOMAIN option to redirect your computer to their block server as aposed to the site you really wanted to visit. Although it’s a trivial exercise to bypass openDNS blocks. There’s also been complaints in the past related to showing ad filled pages instead of a 404 when you try to visit a non-existant domain.