What is a Firewall?

Historically, a firewall was a wall built from bricks and designed by architects to contain a fire within a designated part of a building thus controlling the spread of a fire from destroying other parts of the structure.

In computing terms the firewall is a piece of hardware or software or an integration of the two installed on the computer system or network performing a similar role; preventing unwanted intrusion that may cause damage to a network (or single host) from spreading to the rest of the network or pc.(Komar, 2003)

Tanenbaum (2003) describes a firewall as an "electronic drawbridge" used to inspect the flow of traffic between a network and the Internet and allowing through only the traffic that meets the criteria defined by the firewall administrator essentially keeping out invaders and keeping in the data that is important to the users. This is done typically by packet inspection meaning that every packet is examined by the firewall before it leaves or enters the network; a decision is then made as to what should be done with the packet- sending on or dropping.

A video by Web Warrriors explaining as to how packets travel across a network and the Internet can be found here:-

TCP/IP explained
WARNING- 12 mins long- large file size

Why a firewall is needed and what it can be used for

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