Finding an Address on the Internet – How the DNS System Works
The Internet is a single gigantic network of networks consisting of hundreds of millions of computers, smartphones and other machines linked together by a wide variety of technologies. These include telephone lines, fiber-optic cables, microwave links, and wireless connections.
The purpose of all this hardware is to enable people and machines to communicate with each other.
Many of the computers and other devices linked to the Internet run on a variety of operating systems, such as Mac OS, UNIX, Google Chrome, Android, Windows and Linux.
These operating systems are not compatible and software designed for one operating system usually does not work, or does not work very well, on another operating system.
To enable the machines to communicate with each other, they must follow specific sets of rules. These are designed to overcome the limitations of having a variety of operating systems and are known as protocols .
Protocols provide machines with a common language and method for sending and receiving data.
Without a common set of protocols that all devices must follow, communication on the Internet just could not happen because linked machines that run on different operating systems would not be able to exchange information in any meaningful way.
The two most important protocols used on the Internet are the Internet protocol (IP) and the transmission control protocol (TCP). These protocols establish the rules by which information passes through the Internet.
Without these rules your computer would need to be connected directly to another computer in order to access the information on the other computer. In addition, to communicate with each other, the two computers would need to have a common language.
Before they begin communicating, however, the computers have to be able to find each other. They do so by following the rules of the IP protocol.
Every device on the internet has a unique identifying number without which it would be impossible to distinguish one device from another. This number is called an Internet Protocol (IP) address. A typical IP address is written as a dot-decimal number; eg 192.168.1.1.
In the early days when the Internet consisted of little more than a few computers linked together, you connected your computer with another computer by inputting that other computer's IP address in a dot-decimal format. This was easy when you only had to know a few IP addresses.
The problem with the dot-decimal format is that these kinds of numbers are hard to remember, especially now that the Internet has expanded into a network of hundreds of millions of linked devices.
In the early days Internet users had a text file that linked names to IP address, a bit like a telephone directory. To find the correct IP address for a connection you needed to consult this directory.
Then, as the number of devices linked to the Internet expanded exponentially at an ever increasing rate, keeping this directory up to date became impossible.
In 1983 the domain name system (DNS) was created. This links text names to IP addresses automatically.
Nowadays, to find another website on the Internet, all you have to do is remember its domain name, eg hispage.ie, and the DNS system will translate the domain name into the IP address needed to connect you to the site … all done automatically and invisibly.
But how does this system work? It's simple really.
The Internet includes millions of domain name servers . These are linked together via the Internet and their purpose is to jointly manage a massive distributive database that maps domain names to IP addresses. 'Maps' is geek-speak for 'links' or 'connects'.
When you are trying to access a website, your computer uses a nearby DN server to translate the domain name you enter into its related IP address. You are then connected to the website you are looking for using that IP address.
Conceptually, it's a very simple system and would be in fact except that:
- Currently there are billions of IP addresses in use.
- Millions of people are adding domain names every day.
- At any given point in time, DN servers are processing billions of requests across the Internet.
Because of the truly massive nature of the DNS database, each domain name server only holds a tiny portion of the total database.
This means that when your computer contacts its nearby domain name server, there are several possibilities:
- The server can provide the IP address because the domain is listed in its portion of the database.
- It can contact other domain name servers for the IP address.
- It can redirect the request to another domain name server.
If the IP address cannot be found, you'll probably get an error message saying that the domain name is invalid.
All the domain servers on the Internet are grouped into a hierarchy. At the highest lever are the root DN servers . Below these are the authoritative name servers . There are different root DN servers for the various suffixes (such as.com, .ie, .net, .org, .co.uk, and so on) at the ends of domain names.
The authoritative name servers contain the actual 'directory' information that links domain names with IP addresses.
However, these servers only handle domain names with particular suffixes, eg.ie or.com but not both. And indeed each authoritative name server will only hand a tiny portion of the database relating to a particular suffix.
Suppose you want to connect to hispage.ie, for example. If your local DN server does not have the IP address for hispage.ie in its own database, it will send the domain name to one of the root DN servers.
The root server will not return the address itself; instead it will send back a list of the DN servers that handle.ie suffixes. Your local DN server can ask each of these servers in turn until it gets the IP address for hispage.ie.
DN servers handle billions of requests every day. The workings of this massive distributive database are invisible to the user. The system, nevertheless, is highly efficient and extremely reliable due to redundancy and caching.
There are multiple DN servers at every level, so if one fails there are plenty of others available to handle requests.
In addition, whenever your local DN server gets an IP address from an authoritative name server, it will cache that information, ie retain it in memory for a few hours or a few days so that if it gets the same request from another user it will have the information to hand.
The DNS is a truly most amazing system – it is a database that is distributed throughout the world on millions of machines, managed by millions of people, and yet it behaves like a single, integrated database and handles billions of requests every day!
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