What's in a Name?

For resolution purposes, host names are read from right to left. Similar to finding a city on a world map where you first must find the country in which it is located, in DNS the first information needed is which Domain Server has the records for that top level. For this we turn to the root servers, like a world map shows countries, they tell us where to find the server for the right most part, such as .com .org etc. With that information the request is sent again but to the server returned by the root server query. This process continues until we have drilled down to the target name/IP match. That information is passed back to the client which can proceed with it's task like loading the web page, the process which started the whole DNS request. This process is called recursion or a recursive query and is usually conducted between a users first listed name server and the remote servers, not by the users DNS client itself. Although there can be many requests and responses exchanged to resolve a given host on the Internet, the whole process typically takes only a fraction of a second.

DNS Tree:

root servers
  top level domains
    second level domains
      third level domains
        . . .
          local domain for the target host
            local host

Here is an explanation of the above listing

root servers

-root servers are public servers that know about the top level domain servers. Although they are represented by a trailing dot in a URL, the '.' is implied and generally not required.

top level domains

-these are the right hand side of the name, such as com or net

second level domains

-these often represent an organization, such as example.com

third level domains

-third level domains are the first ones that can be a domain or if it is also the left most part it could represents a computer.

additional levels

-there can be any number of subdomains depending on an organizations needs.

local domain

-this is the most qualified domain that a computer is a member of. It can be any level other than root or top, but is always the second from left most part.

local host

-the left most part is usually a computer name, although it could be a domain. Internally, an operating system can be referenced as localhost.localdomain instead of it's formal name.