Where do you use domain names?

I realize the domain name system isn’t an easy concept to understand. It took bright computer geeks years to perfect it to the point we see it today, and although it works pretty well, the volunteers who maintain the Internet are still tweaking different parts to ensure that we’ll have enough domain names for the foreseeable future.

However, it’s important to have a basic grasp of what is going on with domain names because you simply can’t avoid them in the Internet. They’re everywhere, and you use them constantly everyday, whenever you send email or connect to a web site.

In fact, that’s where we’re going to turn our attention in the next archive since domain names play a huge part in forming email addresses and the URLs (Uniform Resource Locators) that identify web pages.

How to read Domain

So, in postoffice.yahoomail.yahoo.net, the top level domain of net identifies the machine as belonging to an Internet Service provider, or ISP. Obviously, since there are a lot of other ISPs in the U.S., many other machines exist in the net Top-level domain as well.

That’s where the middle-level domains come in handy. In our sample, yahoo is the next part of the domain name (remember, we’re working backward, getting more specific as we go). Middle-level domains help differentiate all the different computers in the top-level domains. So, the word yahoo in postoffice.yahoomail.yahoo.net says that this computer is run by Yahoo. The next middle-level domain, yahoomail, makes it clear that the computer in question is part of Yahoo Service.

Domain name only require a top-level domain and a second-level domain, but there’ no limit on how many middle-level domains a full domain name can have (well, there probably is some limit, but it’s not the sort of thing normal people give a hoot about). You distinguish between middle-level domains by looking at their position in the domain name. The middle-level domain that comes in front of the top-level domain is called the second-level domain, the one before that is the third-level domain, and so on.

We still haven’t uniquely identified the postoffice machine. The remaining part of the domain name, postoffice in postoffice.yahoomail.yahoo.net, is the machine name, and uniquely differentiates that computer from all of the other computers that Yahoo runs.

Now think for a minute about how the domain name uniquely identifies this computer. If you change any part of our sample domain name, you’re referring to a different computer. And, if you change the .net top-level domain, you could be referring to a computer run by a university, government, agency, or non-profit that also has the initials Yahoo.

As a minor twist, domain names are sometimes purely geographical. For instance, a friend of mind runs a computer whose full domain name is memory.ithaca.ny.us. In this case, the top-level domain, ny, puts it in New York State, and the third-level domain, Ithaca, narrows it further to the city of Ithaca. Finally, the machine name, memory, differentiates the computer from all the other computers in Ithaca, New York.

Think about your snail mail address for a moment if you’re having trouble getting your mind around the levels of domain name. Your address identifies your house, your street, your city, your state or province, and your country. Just as each domain encompasses those before it, so does each part of your address encompass the previous parts. The state or province is inside the country, the city is inside the state or province, ad the street is inside the city.

The HIERARCHY OF DOMAIN NAMES

Starting with the top of the the hierarchy, which sits at the end of the domain name, you see the top-level domain of net. There are a small number of top-level domains on the Internet, and they fall into two categories-topical and geographic. Topical top-level domains identify the type of organization that runs the computer in question, and are used mostly in the United States. Geographic top-level domains identify the country where that computer lives, and used primarily outside of the United States. The first table shoes the main topical top-level domains(more may be coming soon, since .com in is filling up) and the second table gives some examples of common geographical top-level domains. Every country has its own top-level domain country code.

Top-level Domain	Organization Type
.com .edu .gov .mil .net .org	Commercial Educational US Government US military Network (ISPs) Non-profit organization

Top-level Domain	Country
.au .br .ca .de .fr .jp .uk .us	Australia Brazil Canada Germany France Japan United Kingdom United States

Why are Domain names important?

Every computer on the Internet needs a unique identifier-Otherwise you wouldn't be able to connect to any specific computer because you wouldn't know how to refer to it. It would be a bit like being at a party where everyone was named John and trying to get the attention of a guy on the other side of the room by calling out his first names.

To solve this problem, the clever folks who have designed and maintained the Internet over the years have come up with the domain name system. Every computer on the Internet is assigned a unique IP address, which is a set of four numbers between 0 and 255, separated by periods. No one stands a chance of remembering more than about three of these IP addresses so these same folks invented the concept of domain names, which replace the numbers with words. Software programs called domain name servers translate between domain names and IP addresses, since people prefer to use domain names when referring to computers, but computers all use IP addresses when communicating with one another.


There are a lot of computers on the Internet, probably several millions. Although there are a tremendous number of words available, especially when you take a different languages into account, there simply aren't enough unique words that are also descriptive to replace an IP address with a single word, like "Tom". The solution name could be the same while other portions could remain unique.

Domain

Imagine being able to identify a single computer on the Internet out of millions, understanding the organizational method by which computers on the Internet are named, and using a powerful database to translate between human-readable names and the numbers Internet computers use to identify themselves. Once you understand the domain name system, you can understand how computers are named on the Internet and how those names are used.



Lingua Internet

• Domain: Since there are so many millions of computers on the Internet, each of which needs its own name, domains make these names unique. Two computers can share the same name as long as they are in different domains.

• Domain name: A domain name is the full human-readable name of a specific computer on the Internet. For instance, the name of the computer that Yahoo uses to store your email is Yahoomail. Every domain name corresponds to an IP address.

• Domain name system: The domain name system converts between the names people use and the IP addresses of computers on the Internet. It has three parts: the technique for converting IP addresses to domain names, the database of IP addresses and domain names, and the domain name server that actually does the conversion when asked.

• Domain name server: A domain name server is a software program (run by Internet service providers) that converts between domain names and IP addresses.

• IP address: Every computer on the Internet has an IP address that uniquely identifies it. IP address are composed of four numbers, each between 0 and 255, separated by periods, such as 205.94.168.255

• Machine name: machine name of a computer on the Internet is the first part of the domain name and differentiates that computer from others in the same domain. For example, postoffice is the machine name of postoffice.yahoomail.yahoo.com

Types of Domain

• Middle-level domain: Domain names have one or more middle-level domains to help differentiate themselves. For example, yahoomail and yahoo are both middle-level in postoffice.yahoomail.yahoo.com

• Second-level domain: The second-level domain is the middle-level domain that comes just before the top-level domain. For example, yahoo is the second-level domain in postoffice.yahoomail.yahoo.com

• Third-level domain: The Third-level domain us the middle-level domain that sits just in front of the second-level domain. For Example, yahoomail is the Third level domain in postoffice.yahoomail.yahoo.com

• Top-level domain: The top-level domain is the final part of a domain name and puts the domain name into a realtively small set of geographic and topical categories. Examples of top-level domain are .com, .edu, .gov, .ca, and .us, which identify commercial, education, government, Canandian and United State domain names, respectively. The top-level domain in postoffice.yahoomail.yahoo.com is .com, and it places that domain name in the network domain.