Firewalls are tools that can be used to enhance the security of computers connected to a network, such as a LAN or the Internet.
A firewall separates a computer from the Internet, inspecting packets of data as they arrive at either side of the firewall ?
- inbound to,
- or outbound from,
- your computer
to determine whether it should be allowed to pass or be blocked.
Firewalls act as guards at the entry points of the computer (which are called "ports")
where the computer exchanges data with other devices on the network.
Firewalls ensure that packets that are requesting permission to enter the computer meet certain rules that are established by the user of the computer.
Firewalls operate in two ways:
- by either denying or accepting all messages based on a list of designated acceptable or unacceptable sources, or
- by allowing or denying all messages based on a list of designated destination ports.
Although they sound complex, firewalls are relatively easy to install, setup and operate.
This page is not intended to serve as a review of specific firewall products.
Rather, it will serve as an overview of what firewalls are, how they work, and the different types of firewall technology and their
suitability for small office and personal computer users.
In order to understand how firewalls work it is important to understand the basics of TCP/IP
, the language or protocol which all computers on the internet use to communicate. If you are not at all familiar with concepts such as packets, ports and IP addresses, please refer to the following page on
If you are, the following section may seem elementary. However, it explains each of the aspects of TCP/IP as it relates specifically to firewalls.
Let us start by saying that TCP/IP is a language that allows different computers to communicate.
On the Internet, this language is spoken and understood by all different types of computers, even those using different
operating systems such as Windows, Macintosh, or Unix.