What's In a Domain Name?
Say "Webster" to an ordinary person
(that is, a person whose life has not been taken over by computers! <g>) and
they may think of the dictionary man, or perhaps the playwright John Webster,
but we, of course, know that the word is really the name for those noble
individuals who devote a part of their life to the propagation of human
knowledge and culture by designing and creating web sites on the Internet!
Names are like that. They have different meanings to different people.
There is one set of names, however, that is a little different. This set has a
specific meaning. While they may be based on words or names in one of this
planet's spoken languages, they designate specific locations on the Internet,
and are therefore held in high esteem by the aforementioned Websters. They are,
as you have already surmised, Domain Names.
"Ah yes," you nod knowingly, "Domain Names." But do you really know what a "Domain" name is and how it works? Many of you do, I'm sure, but it is surprising to me how many questions I am asked that have to do with them, so I thought a little closer look might be a good idea.
Mr. Webster, the dictionary man, tells me that a Domain is "the possessions, estate or land belonging to one person." On the Internet, real estate takes on a slightly different hue. An Internet Domain is a collection of addresses controlled by one server (under the direction, presumably, of a Server Administrator!) A Domain Name's purpose in life is to provide an easy to remember way of discovering a numerical internet address. It accomplishes this through the Domain Name System (DNS) which is a clever, distributed system (meaning it is made up of a lot of computers working together) for translating the name into an address. The translation process is called "Resolving" a Domain Name. A computer involved in the DNS system runs a program called a DNS Resolver. Here's how it works:
A domain name is made up of two parts, separated by a period, like this: domainname.com Technically, this is actually two domains, as you will see, but that's too picky for this type of description! The part following the period is known as the Top Level Domain, or TLD. In this example the TLD is com -- known as "dot com" because it always follows the period (dot). Every DNS Resolver has addresses for "Root" DNS resolvers. These Root resolvers point to computers that can resolve the Top Level Domains. In our example, they would point to one that knows about ".com"s, which would in turn have the address of the system that knows about "domainname". The ".com" resolver is given the information about "domainname" when "domainname" is registered as "domainname.com". This updating is performed by a group of service providers known as "Domain Name Registrars". You go to a Registrar and register your domain name. When you do, they update the TLD resolvers.
Part of the information required in the registration process is the name of the DNS resolver(s) that will hold information about domainname.com. The first of these is called the Primary DNS Server. Information about the domain is updated in the Primary DNS Server, which will then provide this to "Secondary" DNS Servers that will hold a copy of the information for use in the event the Primary becomes unavailable. The TLD servers usually require information about a Primary and at least one Secondary DNS Server, though several Secondaries can be provided.
The Primary DNS Server (and subsequently, the Secondaries) stores information about addresses within the domain. One of the types of address that can be stored is a "Host" address. There are several others, but that's a story for another day! A Host is usually a particular computer. For example, you could have a hostname called "www" (which is very common!) Taken from the initials of the World Wide Web, this name is frequently used to point to a computer that houses (hosts) the web site for the domain. By "point to", I mean that the name is associated with the address of the computer. This association allows a DNS Resolver to translate www.domainname.com into the address of the computer hosting the website. When you type "www.domainname.com" into the address bar of your browser, the first thing the browser does is to use DNS to translate the name into an address to which it can send a request for a web page.
In this way, the Primary DNS Server for a Domain controls all addresses within the Domain. By the way, a Domain can contain a "Sub-Domain" -- as in sub.domainname.com -- which in turn contains Hosts, such as www.sub.domainname.com That too, is a story for another day. Think about it though, and you will probably be able to figure out how it works!