Originally, every server on the Internet was referred to by its IP address. This is a long number, much like a phone number, containing three dots, for example 156.65.234.86. Pretty quickly, however, people wanted to use more of these numbers than they could remember. It was at this point that someone came up with the idea of a system to match names to the numbers. This allowed not only easier web addresses, but also email addresses and many other uses besides.
DNS is a hierarchical system. At the highest level, there are a number of ‘root servers’ (currently 13), most of them in the USA. It is these servers that know what .com, .co.uk and similar things mean. At the next level down, each registry has a master server – so .co.uk has a server that can tell you any .co.uk address.
At this level, ISPs come in. They run DNS servers for their customers, updated regularly by the servers higher up the chain – this process used to take a few days, but now happens in a matter of minutes. Your ISP’s DNS server stores entries to reduce the load on the master servers, but will check occasionally to see if anything has changed, or if you type in a domain name your ISP has never seen before.
There is often a final level, which is the DNS servers that web hosts run for their customers. These are the DNS servers you will be dealing with after you register your domain name. When you type in their addresses into your domain name’s records, it tells the system that those are the servers that know the IP number for your website.
