DNS is short for "Domain name system". It is what helps a computer find another computer on the internet.
Before we answer "what is DNS?", we need to quickly cover what an IP address is. Every device that connects to the internet has an IP address. This is equivalent to a unique phone number for every internet connected device in the world.
Now think about how you use your phone. If you have a smart phone, it's highly likely that it's not just a list of numbers you have programmed in. You will have assigned a name to each of those numbers so you know who it belongs to. Those of you using a landline probably have programmed in numbers into the phone in a similar fashion, or at least have physical list of what number belongs to what person somewhere.
DNS is the internet version of this name to number system. For instance, when you type www.google.co.uk into a browser, the browser goes and checks what IP (number) that memorable name points to (22.214.171.124 in this case), and it transparently takes you there. One could ignore the memorable name and use the internet like a series of phone numbers that you've remembered. One can access that IP directly and get to Google (try it: http://126.96.36.199/). However, as you can imagine, given the number of websites you probably access daily (let alone other services like email), this would very quickly become a lot harder than remembering a handful of phone numbers of your closest friends!
Now, going back to the phone analogy, it could well be that for some of your contacts that they have more than one phone number. They may have a landline, a mobile and a work number.
So, while in your phone, you may have:
DNS works exactly like this, allowing you to have - if desired - your email, website, FTP and any other services split across many servers. Therefore, the list will look something like:
So what if all your services are on one server (just as you may have phone contacts with just one number)? Why not just have one memorable thing listed in your DNS pointing at the one IP address and use that for everything?
There's a couple of obvious reasons for that. Firstly for those managing these services, it means we don't have to remember whether any given client's mail is hosted in the same place as their website. All we need to know is that www. will point at their website mail. will point at their email.
Secondly, it makes it easy to change things later as your organisation grows. When your website is getting a million hits a day, you would want to move your email to its own server! Imagine if you'd just used one bit of DNS for all purposes. You would now need to go into everything that you've told about your email (your PC, your phone, your tablet etc - and in the case of a large company, multiply that by the number of employees) and have to go deep into the setting to make changes. Much better to just go back to that the bit of DNS you've pointed at your email and change it there so that all the devices pick up this change.
The one other thing worth mentioning about DNS is that each DNS server remembers what it has found out for up to 24 hours. This means that when you make a change to a DNS record, it can take up to 24 hours for all the DNS servers on the internet to get your update. This doesn't really affect normal use, but is something to remember when you move a website from one server to another.
If you need help with anything DNS related, please don't hesitate to contact us.