Saturday, 26th August 2006IP Addresses and Network Basics Explained

For those wanted a basic understanding of what IP addresses are, both Public and Private.

Due to the recent explosion of home networks (probably in part due to the ease of deployment provided by wireless networks), I found myself being asked on a regular basis to explain what IP addresses are - this article is my attempt at saving some time. It is by no means comprehensive but simply seeks to offer a vague understanding to those who have never looked under the networking "bonnet" (or "hood" to my American friends!). To get you started, this is what an IP address looks like:

192.168.10.254

What is an IP Address?

An IP address, put simply, is a unique number used to identify a PC (or device). I say "unique" but it really only has to be unique within its network - in the same way that house numbers only have to be unique on their street. To illustrate this, let me give you an example, I have a network at home - it has 3 PCs in it, they have the following Private IP Addresses:

192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4

Where I work we have a small network and the systems there have the following Private IP addresses:

192.168.1.1
192.168.1.50
192.168.1.51
192.168.1.52

As you can see - the IP Address "192.168.1.1" is used on both networks - this doesn't matter as these are two completely different networks and never talk to each other - they are on private networks and so are private IP addresses. To see how this differs from Public IP Addresses, read on.

What is a Public IP Address?

As I mentioned above, IP addresses on a network must be unique - this is not a problem on a small network but on a very large network it can be difficult to keep track of. A perfect example is the largest network on the planet -The Internet (yes - it really is just a network based on the same principles are your 3 PC home network). On the Internet, all possible IP addresses are divided in to blocks and assigned to different companies. Some of these are, for example, Internet Service Providers. When you connect to the internet with your ISP, they generally pick an IP address from the pool of IP addresses they were assigned and loan it to you. This public IP address is different to the IP address used to identify your computer on your own network, its used to identify your modem on the other network you are connected to - The Internet.

Your modem now has the rather tedious task of looking at all incoming data being sent to its Public IP Address and routing it to the appropriate Private IP Address.

Whats the difference between a Static IP Address and Dynamic IP Address?

A static IP address is a public IP address that never changes. If you have a static IP address, when your modem connects to the internet, your ISP doesn't randomly select one their unused Public IP addresses from a list - your modem already knows which IP address it should use. This is useful if people or computers need to be able to identify your network regularly (without having to phone you up and ask you what IP address your ISP gave you today!). Obvious examples of computers that need to always have the same IP address are web and email servers - no email could be delivered if email servers addresses kept changing!

A Dynamic IP address is an IP address assigned by your ISP randomley. You can also call IP addresses on an internal network "Dynamic" IP addresses if they are assigned to PCs "on the fly" as is often the case - this is a subject in itself called "DHCP".

Where do Domain Names fit in?

A domain name is simply a useful naming system of Public IP addresses, devised to make things easier for us lowly humans (computers do not need them) - its much easier for me to remember www.Google.com than it is ro remember 64.233.187.99!

If you like, you can still use Google's IP address to visit their website, click here to give it a go: http://64.233.187.99.