Why Do We Need It?

Before we go into the details of how DNS works, let's take a quick look at what we are trying to achieve and what alternative ways there may be of doing this. Let's assume we are trying to access a machine somewhere in the world that contains a software package that we need to download. To connect to it, we need to first determine its IP address, which we may be able to do by carrying out one of the tasks listed here:

• Phone the administrator and ask what the address is. Obviously this is not very practical; we probably wouldn't even be able to find out who the administrator is at most companies. Even if we got the IP address, we would have to store it (probably in our local hosts file) and then check that it hadn't altered the next time we wanted to connect to it.

• Let someone maintain a global hosts file. Not as funny as it first sounds—this is the way things used to work before DNS came around. The file was maintained by the Network Information Center (NIC) and distributed as it changed. This soon became impractical simply because of the number of hosts connected to the Internet.

So, let's see how DNS works and helps us to get around these issues. To do this, we'll break it down into some of its component parts and explain what they do, before finally bringing them all together for our system.