For example, when you type www.google.com in your browser's url bar, a DNS server will be required to look up and resolve the domain name google.com into its corresponding IP address (173.194.36.157) .With millions of different websites on the Internet today, it would be nearly impossible for any individual or computer to store every website and their corresponding IP addresses locally; therefore, we need a service that acts as a global directory list of every single website in the world along with their corresponding IP address.
Let's talk about a couple important parts of these server types first: addresses, queries, answers, time-to-live (TTL), weighting and priority.An address in this case is just a reference to another system or network.
Queries are the request for information that you make to other computer systems; so when you go onto your favorite search engine like Google or Yahoo!, you make a query asking them to look up some information for you.
The answer is what they find as a result of your query.
Each answer has a TTL that tells you how long the server can store this information before expiring and having to be renewed again by another query; weighting is just an algorithmic process in which DNS servers can rank their responses with, taking into account various factors such as the number of times they have answered before a certain query; priority is a numeric value assigned to each DNS server which determines how it will respond to queries compared to all other servers out there (or even within its own particular domain).Now let's look at recursive and authoritative types of DNS servers.
The main difference between recursive and authoritative servers is that recursive servers are not technically supposed provide the final "answer" but instead should reference other sources for the correct answer (the "authoritative source").