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< Previous Section: Firewalls - The First Line of Defense

2.1      What exactly is a Firewall?

It is refreshing in an industry filled with cryptic terms and three letter acronyms (better known as TLAs) to come across a name that is at least somewhat self explanatory.

Consider the internet to be inferno of viruses, hackers and cyber criminals all looking for systems that they can invade. Rather like a firewall in real life it stops any of this unpleasantness from spreading into your environment. Another good analogy is that of a fortress wall that protects the inhabitants that live inside. The firewall stops unwanted connections from entering your internal network much like the wall around a fortress prevented the marauding hoards in medieval times. Rather like the gate in the fortress wall the firewall allows only data and connections that meet certain criteria to pass through the wall to the internal network.

A typical firewall configuration is shown in Figure 2.1. The firewall is positioned between the outside internet connection coming in through the modem and the internal network on which reside a number of Linux and Windows systems. The firewall controls all data traffic and filters out anything that is not permitted to enter the internal network.

 Linux Security Firewall diagram
Figure 2.1 - A typical Firewall Configuration

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