CPS100 • INTRODUCTION TO COMPUTERS

Now you know about WANs and LANs, what a server is, and how data is exchanged using protocols.

How does that connect with the way we use the Internet? You do not, after all, type in IP addresses to look up web sites.

What is a domain? Put simply, a domain is an address on the Internet which is maintained by various servers (e.g., email servers, web servers, etc.). We usually think of a domain as containing a "web site," but domains can contain much more than just that.

For example, the domain luj.tokyo has a web site—this one. Therefore, it has a web server, software on a computer somewhere which serves web site documents to browsers making requests.

However, it also has email; I could make email accounts using the domain, like "admin@luj.tokyo"; therefore, the domain also has email servers.

The domain can have other servers as well: file servers, database servers, and so on. Each uses the domain name in its address.

If you own a domain name, then that name could be used to host a variety of different types of information—not just web pages.

Domains and IP Addresses

So, if you have various kinds of information on these servers, how do people connect to it? The servers are located on a network, therefore they have IP addresses to identify their locations.

However, IP addresses are much too difficult to remember. Seriously, could you imagine someone saying, "Check out my web site at 2001:0db8:85a3:08d3:1319:8a2e:0370:7334"? Me neither.

As a result, we needed a better way to express an address on the Internet. That's what domain names are for.

Each domain name is connected to an IP address. In a way, they are the same thing; you can type an IP address directly into a browser. Go ahead, try this address: http://205.213.172.104. That will take you to a placeholder page for Lakeland University.

lakeland.edu = 205.213.172.104

Think of it in the same way as you think about a phone number. If you want to call somebody, you tap out their telephone number. However, if your cell phone is smart enough, you would simply look up their name, and the phone would automatically find the right number and connect you.

More and more web sites are increasing their security so that direct IP address access is not possible. A few still work, for example:

That's what browsers do: when you type in a domain name, they look up the IP address for that domain name and they take you to it. This is done by the Domain Name System (DNS).

When you enter a URL, it is sent to name servers which identify the domain name, and then identify the IP address connected to the domain name. So, if you type in the domain name japan.lakeland.edu, the DNS system returns the address 119.245.180.222. That number address allows the exact computer to be identified, and the request is sent there.

A domain name has several parts:

• HTTP protocol: states that the transaction uses the HTTP protocol
• web server: defines the web server (not the mail server or FTP server)
• subdomain: a subdomain is a directory set aside to be a special part of the domain, instead of being a directory within a domain (such as http://www.lcjapan.com/cps100/)
• domain name: the name of the domain being used
• top level domain: the category of domain being used

Most people are used to typing the letters "www" before a domain name, as in "www.lcjapan.com". That "www" refers to the part of the domain "lcjapan.com" which is reserved for the web site—the web server. There may be other servers on the domain used for email and other network connections, using various protocols:

Top-level Domains (TLDs)

Top-level domains usually note which category a site belongs to. For example, a .com site is supposed to be commercial; a .org site should be an organization, usually not-for-profit. There is no rule that says a site must follow the rules for .com or .org, but it is expected that top-level domain names will be chosen to match the nature of the site.

Top-level domains come in various types, but the main ones are .com, .net, and .org for private web sites, and .gov, .edu, and .mil for government, educational, and military web sites. Some TLDs, like .gov, .mil, and .edu are reserved for special use and are only given to people or organizations that meet the requirements. For example, .edu is given only to accredited educational institutions, and only one domain name is allowed per school.

These are just a few of the many TLDs, however; there are many more:

There are more, and new ones are created from time to time. For example, this site uses .tokyo, a recently created TLD. Here are a list of some of the newer TLDs:

National Domains

Each country has a domain, which it controls. Some examples:

These are usually used with 2-letter versions of the common suffixes, such as ".co.jp", ".ne.es", and ".or.zw".

Each country controls the use of its suffix, and can charge whatever amount of money that it likes. The ".jp" suffix is sometimes pretty expensive.

One country became rich because of this naming system. The tiny country of Tuvalu did not get ".tu" because Tunisia is before it, alphabetically. So Tuvalu got ".tv". However, there are rumors that when Tuvalu eventually disappears because of global warming, the ".tv" domain suffix will also disappear.

Recently, the fact that countries control domains has hit the news. There are services which create mini-URLs, to replace longer URLs which will not fit in Twitter or other short message spaces. The most famous is called bit.ly, and an example address is one I have created for this web page: http://bit.ly/2fRHo2q. Click on that, and it will expand to "http://cps.luj.tokyo/in03.php" and take you to this web page.

The problem? Well, these shortening services decided to end with the "ly" domain, as a cute, short, and easy-to-remember suffix. But the "ly" domain is owned by Libya, not recognized as a liberal, free-wheeling place. Libya has "morality laws," and a web site with the domain "vb.ly" was seized and taken down by the Libyan government for "promoting illegal activities"—namely, shortening URLs to pornography sites.

To sum up, when you type a domain name into a browser, the name is sent to a DNS server. The DNS server identifies the TLD, and then the domain name, and then identifies the IP address of the server hosting the files for that domain name.

Domain names have several parts, including subdomains, which can be parts of a domain, and the top-level domain, or "TLD," which identifies the category of the web site. TLDs can be country names.