DNS, the Domain Name System, is concerned with converting domain names like menandmice.com into IP addresses that you can connect to like 193.4.171.25.

Before DNS, mapping of names to IP addresses was dealt with by a phone book like file that administrators kept a copy of and updated every few days.

As of this writing there are just under 22.4 million registered com second level domains, 4.3 million net domains, and 2.7 million org domains. The various national domains count for millions more. What is more, this vast ocean of domain names is constantly moving as hosts change IP addresses, new domains are added, and domain names are sold or re-assigned.

This is no place for a static file; what we need, and what we have in place, is a brilliantly designed distributed database called the Domain Name System.

The key to DNS is delegation. The root servers are ultimately responsible for all DNS information. However, the root servers have delegated responsibility for each top level domain to top level domain servers, like the ones that serve com. The com servers are responsible for all domains ending in com, but they delegate responsibility for second level domains like menandmice.com. The servers for menandmice.com can then delegate further. Eventually this chain of delegation will reach a server that can answer the question.

The DNS system is very robust. Most domains are delegated to more than one server. For example, the com domain delegates responsibility for menandmice.com to three different name servers. Even if two of those servers were to crash, menandmice.com’s DNS information would still be available.