There are a huge amount of buzz words and confusing terms surrounding the internet and computer networking that makes it very difficult to understand for the everyday person. This article attempts to shed some light on the confusion and give you a broad overview of what happens when your computer connects to the internet.
Lets think about a network that most of us navigate and use almost every day without thinking it complex – the road network. The roads provide the way to get from source to destination and the cars provide the mode of transport. Keep that image in your head as you read through the following paragraphs.
Source and Destination
In the road network a source or destination can be thought of as a house or building address. In computing terms this is called an IP address and is of the form 126.96.36.199 – that is 4 sets of numbers from 0 to 255 separated by a dot. Other examples are 192.168.1.23, 10.0.0.1, 188.8.131.52 Just as each house address is unique, each IP address is unique.
How do you get an IP address then? This will differ from computer to computer depending on how yours is setup and what you use it for. One thing for sure is if you want to communicate on a computer network (like the internet) you will definately have an IP address.
Unlike a house address which never changes, your computer IP address may change from time to time. There is a limited set of unique IP addresses so they can’t just give them out to everybody. What normally happens is you lease an IP address for a set period of time while you need to use your computer and then free it up for someone else to use while you don’t need it. This process is hidden away from users so you don’t have to concern yourself with it. If you really want to know – something called a DHCP server is responsible for allocating you an IP address and telling you how long you can lease it for.
You’re probably thinking that you’ve never come across an IP address before yet you’ve been happily surfing the internet for months. Humans aren’t so good at remembering strings of numbers so we use domain names instead. Examples of domain names are www.google.com, www.bbc.co.uk and tilion.org.uk. Notice that they don’t necessarily have to start with www and they don’t all end the same (the endings are actually predefined and vary from country to country apart from the main three which are .com, .net and .org.
A domain name can be thought of as an easy way to remember an IP address. Servers known as Domain Name Servers (DNS for short) are responsible for converting the domain name you enter into a web browser, into the IP address to locate the machine hosting it. Again this happens behind the scenes and most users are totally unaware.
Unlike the road network, where you can see the cars travelling around from source to destination, a computer network sends electrical signals along wires (or wirelessly). The road network of the computer world is known as TCPIP and describes a way for your communication to travel around. All you really need to know is that if you try to contact another computer at a specified IP address (or domain name) the communication will succeed providing there are no broken roads between you and the destination.
Remember how an IP address identified a particular computer somewhere in the world. Most computers do more than one thing at once so there needs to be a way to differentiate between the services offered so the computer knows how to reply – this is where ports come in. An IP address can be likened to a house address, so a port can be likened to a way to enter the house (front door, rear door, window, sky light). A computer port is a number from 1 – 65535 (yep, it has a lot of ways to get in!).
One of the most popular services offered by other computers is serving web pages (known as HTTP or Hypertext Transfer Protocol). The HTTP bit is the way you have to speak to the server at the other end so it can understand you – think of it as speaking english or spanish and you must both be speaking the same one. Don’t worry too much about speaking HTTP as your web browser understands how to do that for you. Web servers typically listen on port 80 so when you type http://www.google.com into your web browser, 80 is the default port it uses to communicate with the other computer. http://www.google.com is exactly the same as typing in http://www.google.com:80 (the :80 mean use port 80). If you try to communicate on a different port the chances are noone will be listening or maybe the service that is listening doesn’t speak the same language as you, e.g. http://www.tilion.org.uk:22
Remember that the specified (or default) port is the one used on the server. Your computer is also using a port to talk to the server, but which one you shouldn’t worry about aside from the fact it will NOT be the same port as the server is using.
Some other services you’ve probably used already and not realised are;
- port 110 – POP3 which is used to get your emails
- port 443 – HTTP in SSL mode which is a secure way to view a web page and is used for sensitive information like banking
Technical readers can probably spot mistakes in the analogies, but I’ve tried to keep technical detail to a minimum for the sake of understandability!