Many people who register domain names are IT experts and need no introduction to how DNS works and how your domain names end up showing you a web page. For those who aren't, however, here's a much simplified guide to try to demonstrate what DNS is and how it brings your domain names, and your web sites, to your customers.
What is DNS?
DNS stands for Domain Name System. In short, it's the system by which computers all across the globe (that are connected to the internet) can talk to each other and be referenced. Rather than being forced to remember lots of numbers that ordinarily reference these computers, DNS provides us with names that are understandable to humans - like google.com.
Discussion of IP addresses
Before we go much further we have to introduce the concept of IP addresses. If you're not sure what an IP address is, you've still probably heard the term plenty of times. Effectively, each device that is connected to the internet is assigned its own IP address. This IP address is completely unique - it identifies each source of contact on the internet - and that's the beauty of it. In most people's homes, there's just one device that's actually connected to the internet and is either a router or a modem. This device is assigned a completely unique IP address and uses this identifier to send and receive information from around the internet.
IP addresses are most often (currently) in the form of 000.000.000.000 where each set of numbers is called an Octet. These octets can range from 0 to 255. These types of IP address are sometimes called IPv4. There is another more recent and more expandable version of IP called IPv6 which uses hexadecimal expressions to signify larger ranges.
For most people, their own IP address is assigned by their ISP (Internet Service Provider) and will rarely be forced to examine it. Where people do more often come across IP addresses is when they try to access a website - but it is the DNS system that hides this clunky bunch of numbers from sight. What users therefore usually see instead is the domain name - the web site address that we see in our browser's address bar.
So - as we can see, DNS is a sort of translation service, turning ugly numbers like 173.194.367.104 to far less cumbersome things like google.com. And aren't you happy for that?!
How does DNS tell people that my web site is at a particular IP address?
Specialised computers, more usually known as DNS servers, exist to tell people exactly which domain names map to which IP addresses. There are literally hundreds of thousands of these servers, all specifically tuned for this one purpose.
DNS servers hold lists of IP addresses and domain names. When a request is made to a DNS server to do this translation, how it responds depends on a few things:
- How old its data is for that translation
- Whether it's ever done that translation before
If its information is either deemed too old (up to 72 hours) or it's never looked it up before, the DNS server has to go and find the information from elsewhere. No DNS server holds all up-to-date information for all domain names and IP addresses... it would be a huge list and would force all internet connections to ask the same source - which would be slow and bad.
Instead DNS servers are spread across the whole globe - and they talk to each other constantly in order to retrieve the right information to map any particular domain name to its correct IP address.
How does a DNS server really know?
Each domain name will have at least one DNS server which it specifies as the authority for that domain name. That DNS server will know exactly which IP address maps to that domain name. So, if any DNS server at any point along the line doesn't have information to translate a web site address to an IP address - eventually it will ask the authority DNS server for an answer.
Real life example of DNS working
Whenever you request a web site from your internet browser (let's keep with the theme and say we're looking at www.google.com) - what actually happens is that you browser will be forced to jump through a few hoops before it can retrieve that hallowed google search page.
Please note: the following is simplified for ease of reading and understanding.
- Your browser needs to be able to ask the Google server for the page you've asked for. To do that, it needs to translate your request for www.google.com into that IP address we talked about, which is a unique identifier for the google server, and which will respond with our web page.
- Your browser may first check on your own computer to see if it already knows what IP address www.google.com uses. If it does, skip straight to number 6.
- No joy yet? If you're inside a business then it's possible that you have your own DNS server. If it has an answer for you (perhaps someone down in marketing has been googling before you!) then it'll respond without having to ask any more questions out there in the world of DNS. If so, skip to 6.
- OK, we couldn't get an answer from our local environment. Well, our next step is to ask our ISP. They have their own set of DNS servers that are assigned to us and so if anyone using the same ISP as you (eg. the whole of Virgin, BT, demon, Sky, etc.) has been on the google website in the last few hours, it's bound to already know which IP address to go to. Yes? Skip to 6.
- Wow - no-one's used Google on our ISP for a bit. So your ISP's own DNS servers are then going to go and ask another DNS server to see if they have the information they're looking for. It may go to another friendly DNS server further up the line, or may just jump straight to the authority DNS server for your domain name.
- Finally! We got an answer. www.google.com translates to 173.194.37.104. Our browser now goes and knocks at the door that's numbered with that IP address and will send you your web page.
Hope that helped clear up a few queries about DNS and domain names.
