I like this kind of thing. According to the ICANN blog there are – based on robust estimation techniques from collected DNS data – at least ten million DNS resolvers on the internet, yep ten million. Or more. DNS resolvers are the machines that do much of the water carrying on the internet: caching (or in English, ‘remembering’ for a few hours) results from the authoritative DNS servers on the registry (the root servers, the top level domain registry servers and so on). Without the practice of caching the internet would grind to a standstill. The principle is a pretty good one: after all the IP addresses (the numbers that machines recognise each other by) that locate http://www.google.com, for example, are very likely to be exactly the same as they were four hours ago. And they are very likely going to be exactly the same in another fours hours: Google is not going to move their hosting infrastructure very often, which is one of the reasons these IP addresses might change.
And those root servers? Many people know there are thirteen root servers. Unlucky 13 perhaps. Well not exactly, as in fact like any machine with an IP address it can be replicated. And low and behold that is exactly the case. Here is a pretty cool root server map showing the root servers and their global replications:
Take a look for yourself at the Google map here