What is a firewall ? (Non geek version !)

Somebody ask me what is a firewall. There are a lot of definitions out there for a firewall � but most of them are written by geek for geeks. So I will try to explain in a non geek way the general idea what firewall is.

First about IP�s and stuff. So you know that all the computers in internet have addresses that are something like 72.14.207. 192 (this for example is the blogspot IP address ). So the IP addresses are some number formed by 4 small numbers (between 0 and 255). There are also other kinds of notations but this one is the most used. So every computer connected to internet has an unique one. Sometimes the computers don�t have there own IP address; imagine that you are staying with parents so you don�t have your own address but the parents address. And if somebody tries to send you a letter it using your parents addresses but is writing on envelope �For Jon� assuming you are the only Jon in the family. This is called private address spaces and are usually 192.168.x.x or 10.x.x.x. Everybody can have a Jon in the family but when you say Jon only your family know about what Jon we are talking about. But you are not sending letters with the address Jon but the parents address.

Second element is the port. Every compute has ports (65535 of them). Ports are kind of type of services are offering. So for example imagine that you have announced in the newspaper that you lost your dog and also that you find a cat. When somebody sends you a letter will say something like �Regarding about your announce in the paper that you lost your dog. I found �it�. This are called services and every one has a port. For example to get the web pages from Blogger your browser is connecting to the Blogger address on port 80 that means something like About the thing with pages that you are giving: Give me the page of Jon

If you are connecting to a different port for example 25 is for sending mail and try the same request will mean something like Please send this email to: Give me the page for Jon so it don�t make sense. You have to send the request to the specified port.

So,now the very fast definition what is a firewall is a set of rules that are saying something like this:

• If you are from Minnesota don�t ask me about the found cat because I am in California
  
  
• If the address on the envelope is just Jon and I don�t have a Jon in my family throw it away.
• If is from Jon and I am Jon , can't be from me so is something wrong with it throw it away.

So it kind of thing like sorting mails before you even open them just based on the address.

Even more, the viruses try to exploit some services like for example your mother will buy every kitchen item that is promoted. So your father don�t want to spend all the money on that kind of stuff so if it see that the mail is for your mother and say something like About kitchen items, or is form Big kitchen company, he will throw it away before your mother see it, protecting her.