You visit websites every day, sites with names like Google or Wikipedia and with addresses like google.com or wikipedia.org. Most of us don’t take the time to think about what that address means, or how the address system works. It’s a shame we don’t appreciate this more, because the Domain Name System — the system that makes it possible to find a website by typing in a name — is one of the key innovations that makes the internet work.
What is the Internet?
The internet is nothing more (or less) than a network of computers (or, more accurately, a network of networks). Lots of different computers have content — websites, documents, databases, pictures, application, videos — which the owners of those computers make publicly accessible. All these different computers are linked together to form local networks, which are linked to form regional networks, which are linked to form the world wide web — the network of networks we call “the internet.”
How Do Computers Identify Each Other?
Computers identify each other using long strings of numbers — identification numbers we call “IP Addresses.” These numbers are generated by the computers themselves according to algorithms and systems which guarantee they will be unique. Much like telephone numbers, there are tiers of uniqueness — many people may have the number
867-5309, but only one phone within the
321 area code has that number, and there is only one
321 area code within the United States.
IP Addresses, like phone numbers, make it easy for the computers to communicate with each other but — again, much like phone numbers — they are not particularly meaningful to humans. You might be able to memorize a phone number (especially if you set it to music, but it is much easier to use a phone book or directory.
The Domain Name System
The Domain Name System is that directory. Rather than requiring everyone to keep their own directory and making users type meaningless numbers into their browsers, the DNS maps domain names to IP Addresses.
The Domain Name System is a distributed directory — there is not one, single authoritative list that has every single domain name and its associated IP Address. Rather, responsibility for groups of addresses is divided into domains.
In pre-internet English, a “domain” referred to two different concepts:
- A territory over which an authority exercises control
- A body of knowledge; a subject area.
It turns out that both of these make a lot of sense for how the domain name system works: the authority for each domain exercises control over that domain by being the recognized “expert” (or authority) on a particular body of knowledge — the knowledge of which domain names should be associated with which IP Address.
You can visit Google using either a domain name or an IP address. Try clicking each to see what happens.
The root domain in the DNS is the DNS itself — the entire internet. ICAAN (the Internet Corporation for Assigned Names and Numbers) exercises authority over the domain name system as a whole.
Below the root domain are the Top Level Domains (TLDs). These are well-known as domain-name extensions:
.edu, and so forth.
ICAAN has the final authority over who manages each of those domain name extensions. It exercises that authority by managing the root nameservers. What do the root nameservers do? They tell you where to find information on the TLD nameservers.
Each TLD nameserver has information on the domains under it — or, more precisely, it has information on each domain’s nameserver. The domain nameserver is the one that finally tells you the IP Address associated with the domain name that you are looking for.
This is easier to understand if you follow how a request is made by your web browser.
Converting a Domain Name Into an IP Address
You want to visit a website with the address
example.com. The following things happen:
- Your browser sends a message to the root nameserver: “Where can I find
- The root nameserver responds with information about the
- The browser now asks the
.comnameserver the same question, “Where can I find
.comnameserver responds with information about the
- The browser send the same message to the
example.comnameserver, “Where can I find
example.comnameserver tells the browser the IP address to use for the request.
- The browser sends a message to the IP Address specified.
- The content at
example.comis delivered to the browser.
The Purpose of TLDs
The different “domain extensions” or Top Level Domains each have generally-recognized meanings, only some of which are officially enforced.
Some of the more important TLDs include:
.com— Commercial sites. This is the most popular, and most valuable, TLD.
.org— Generally understood to mean “non-profit organization,” but that is not an enforced rule. Anyone could use a
.orgdomain name for a personal or even a commerical (for-profit) business. (Though running a
.orgsite as a business seems, at the very least, misleading, and may be unethical.)
.edu— This is used only for colleges and universities, and its use is restricted.
.gov— Used only by the United States Government.
While other TLDs are growing in popularity, the .com TLD is still the most recognizable, and is used by more than 50% of all websites.
There are many other of the
gTLDs, or “Generic” Top Level Domains. There are also country-code TLDs (ccTLDs), which are used within each country —
Country code domain names are the only two-letter TLDs — all others are three letters or more. Sometimes, country-code TLDs have been used as if they were generic TLDs. This happens when the country-code has another meaning. For example, Tuvalu’s code is
.tv, which is used frequently by video sites.
There are also many “new” or “extended” gTLD names, made available over the last few years through recent action by ICANN. These gTLDs, such as
.club open up a wide range of possible domain names.