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Protecting Your Data: A Guide to Windows Firewall


CHAPTER 1: WHAT IS A FIREWALL?


To building architects and construction engineers, a firewall is a solidly-built wall designed to prevent a fire from spreading from one section of a building to another. In computer networking, a firewall is a solidly-built piece of software or hardware that prevents unauthorized network traffic from spreading from one part of the network to another.

At its simplest level, a firewall is a filter between your computer and the rest of the world. For example, a firewall can be configured to allow your computer to view web sites but restrict file transfers. In most cases, firewalls go beyond the capabilities of a simple traffic filter. Today's firewalls are often "stateful," because they keep track of all conversations across the network. If unsolicited web traffic was received from the Internet, a stateful firewall would identify this unwanted data and drop the traffic before it ever reached your computer.

Without a firewall, all traffic moves from the Internet directly to your computer. In this diagram, the "good" traffic is colored green, and the "bad" traffic is colored red.


Windows Firewall adds an additional level of security by examining each piece of data. If the data is good, it passes through the firewall and reaches the computer. If the data is identified as bad traffic, the network packets are simply dropped and never make their way to the computer. Although this diagram shows the Window Firewall as a separate icon, the Windows Firewall is software that physically runs on your computer.


As this diagram shows, Windows Firewall intercepts all network communication to provide protection against unauthorized network traffic. This protection exists if this traffic enters your computer through a modem, a wired network adapter, or a wireless network connection. Windows Firewall protects your computer regardless of its connection to the Internet!