Ever wonder how your computer finds all those websites? : an explanation of DNS and how it works.
DNS, the Domain Name System, is the directory services of the Internet. Without it, all of those easy-to-remember names like google.com would just be a bunch of numbers.
Like the telephone system, every device attached to the Internet has a unique number, its IP address. Also like the telephone system there is a directory services to help you find those numbers called DNS.
If you have someone's name and address you can call a directory services, give them the details you know and they will (usually) give you the telephone number to call them. Likewise, if you know a server's host name (maybe http://www.google.co.uk/) you can give that name to a DNS server and it will give you the IP address of that server.
Why do we need DNS?So, DNS converts host names into numbers. What use is that? Well, humans tend to like names, they're easier to remember. Computers, on the other hand, like numbers, and since the Internet runs on computers it does things it's own way. DNS is provided purely to make things easier for us humans to understand (it's a bit like The Matrix - you can watch the numbers go past if you really want to, but its much easier to look at the translated version).
Like a physical address, Internet domain names are heirachical (only a little more strict), so while your address might look like:
| House name: | 76 Buckingham Palace Road |
| Town: | London |
| County: | London |
| Country: | England |
An Internet domain name looks like:
| Host name | www |
| Domain | |
| Second level domain | co |
| Top-level domain | uk |
As with physical addresses, the exact layout can change. Sometimes there will be more parts to the address, so in the same way that houses can be divided into condos or apartments, domains can be divided into subdomains (there could be a domain name like "www.images.google.co.uk" for example). Sometimes there will be fewer parts - typically the larger the organization, the shorter their domain name, ibm.com for example.
There are only a few top-level domains and creation of new ones tends to cause a lot of arguments so the main ones being:
- com
- org
- net
- Country codes (fr for France, it for Italy, uk for Britain, etc.)
Useless trivia: The "uk" country code should be Ukraine and Britain should be using "gb", but for historical reasons Britain uses "uk" (United Kingdon) and Ukraine ended up with "ua".
Second level domains aren't quite so restricted (you can have pretty much whatever you like under "com", "org" or "net"), although typically each country has its own version of "com", "org" and "net" and the actual domain lives under that.
There are two key parts to the DNS:
- DNS server
- The DNS server is the part of the system that stores the domain name and IP address details. It's a bit like a phone book. There are loads of DNS servers on the Internet, all looking after different domains (just like there are loads of different phone books, each covering a different region).
- DNS resolver
- The DNS resolver is responsible for looking up information in a DNS server. It's the Internet equivalent of the voice at the end of the directory service. Typically each organization has its own DNS resolver (most people use the one provided by their Internet provider).
If, for example, you wanted to speak to the sales team of a company, but didn't know their number the process would go something like this:
- You call directory services and give them the details.
- Directory services will look up those details and give you the main switchboard number.
- You call the switchboard and ask for sales.
- The switchboard connects you to someone in sales.
Now, say you wanted to find the host name of that same company's web server (we'll use www.google.com), the process is:
- You ask your local DNS resolver for the IP address of www.google.com.
- The DNS resolver asks a root name server.
- The root name server doesn't know the IP address, but responds with the name of a DNS server that looks after the .com domain instead.
- The DNS resolver asks the .com DNS server.
- The .com DNS server doesn't know the IP address, but responds with the name of a DNS server that looks after the google.com domain instead.
- The DNS resolver asks the google.com DNS server.
- The egoogle.com DNS server returns the IP address (72.14.207.99)
- The DNS resolver gives you the IP address.
It's a little more complicated, but basically the same procedure. That's how your computer knows where to go and what information to display when you type www.google.com. DNS is taking that name and pointing your internet browser to 72.14.207.99 and you see the familiar webpage we all know as Google.
Thank you for being a loyal Cetrom IT client. We will continue to provide you tips, tricks, and information regarding the IT industry so as to help your productivity at work and at home.
Sincerely,
--The Team at Cetrom Information Technology
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