URLs and domain names

To get to a Web site, you have to click on, or type in, its name in a Web browser. The name of the Web site is technically referred to as a URL (Uniform Resource Locator) and looks something like this:

http://example.com.

A URL consists of two parts, the "http://" which tells the browser to use the HTTP protocol to get to your site, and your site's name, "example.com" which is technically called the site's domain name. A domain name is a human-understandable and unique name for your site.

Notice that a domain name consists of a series of strings separated by dots. Each string within a domain serves to make the overall domain name unique. For instance, suppose there are two companies both called "MyCo Corporation" in, say, the US and India. Then, they could be assigned the domain names myco.us and myco.in. Thus, both of them have the string "myco" in the domain name, but the suffix "us" or "in" makes them unique.

Domain Name Registrars

To keep things manageable, the Internet authorities have created a set of "top level domains" like "com", "net", "org", "edu" and so on. A Domain Name Registrar is given control over one or more of these top-level domains.

Anyone who wants a domain within a top level domain (that is, a domain name ending in the top-level domain's name) contacts a Domain Name Registrar and asks the registrar to register their name. The registrar ensures that the name is unique, and, for a small fee, registers the name. For instance, if MyCo Corporation would want to own the domain name myco.com, it can contact the Domain Name Registrar for the ".com" domain and ask the registrar to register the domain name myco.com. Once this is done, anyone can type myco.com and get to the myco.com site. There are many Domain Name Registrars, and some of them, like register.com are very popular.

Host names and IP addresses

When you type in a URL into a browser, your computer has to contact the computer on the Internet (also called a host) that contains the Web site with that name. For example, if you type http://myco.com in your browser, your computer has to contact the computer that hosts the myco.com Web site. It does so by sending a packet (a small amount of data) to the myco.com computer saying "show me the main page of the myco.com Web site". The myco.com Web site replies with the main page. To make this work, the Internet has to somehow transmit packets from your computer to the computer that hosts the myco.com Web site. While the myco.com computer is easily identified by its unique domain name, it is really much easier to transmit the packet if the destination is identified by a number rather than a name. The number that corresponds to a domain name is called a computer's IP address, for example 129.31.212.144.

Every computer on the Internet and every Web site must correspond to an IP address. Your Web site hosting company will provide you with a set of IP addresses that you can allocate to the Web sites that you create.

IP-based and name-based Web sites

There are two ways to host domains. The first is to create the domain with its own IP address. This is called IP-based hosting. You must create IP-based domains if the domain needs anonymous FTP and its own secure-site (SSL) support.

The second way to host domains is to create a domain that shares the primary IP address of the server. This is called name-based hosting. Name-based domains receive most of the benefits of an IP-based domain without occupying an IP address.

All of the standard sets of server applications are available to IP-based and name-based sites, except SSL encryption. SSL is not supported for name-based sites.

IP addresses happen to be scarce resources. To conserve IP addresses, you can arrange to have many sites share the same IP address.