Introduction.

What is a firewall?

Just as a building has a firewall and possibly a fire door to try to isolate a fire on one side of the wall, preventing it spreading to the other side, a computer firewall does much the same. However, it's not concerned with fires, but more to the point, unauthorised entry and use. It most commonly, sits between the computer and the Internet, although in complex networks, there can be others within the overall system.