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In simple terms, a firewall serves two primary purposes. First, it protects computer systems and networks from malicious activity coming across Internet connections. Second, it also provides computer network administrators with control over the types of communication that can be conducted over Internet connections within a specific computer network.
The first purpose is similar to the purpose of the anti-virus and anti-spyware software you may be using on your home computer. Viruses and automated programs that have been written for malicious purposes can attack any Internet-connected computer in a variety of ways. Anti-virus programs may catch these, but a firewall acts as a communications filter which can stop those malicious communications from ever reaching your computer in the first place.
The second purpose is less common with home computers and computer networks, but is very common in companies with several Internet-connected employees and at least one IT specialist. In these situations, a firewall can be programmed with specific, customized rules that may restrict employees from visiting websites that are unrelated to business goals or that may pose security risks. In companies that deal in highly sensitive or confidential information, a firewall may have very rigid rules programmed to help protect that information. -
Most firewalls actually fulfill their purpose by maintaining lists of rules for filtering data and of characteristics of both "safe" and "unsafe" data. Whenever a user sends information via the Internet, it passes through the firewall first, allowing the firewall to filter the data according to the standards set by the network administrator. When data attempts to come from the Internet and into the computer, the data is again passed through the series of filters and any bits of data flagged by the firewall as being "unsafe" are discarded.
The filters can be customized to restrict information and communication in a number of ways. One of the more sophisticated customization settings is the ability to ban content by certain words or phrases. This option is sometimes used by companies to prohibit their employees from accessing pornographic websites and other sites with content that would be inappropriate for the workplace. A firewall can also be used to block access to specific websites, such as popular personal email sites. It can even be used to block specific IP addresses, which are the distinct numerical identifiers assigned to each individual computer.
These last several examples are settings that are most frequently used within companies and organizations, and are usually only used in private home computer networks as a means of establishing parental controls. Home computer users often find that firewall software is built into either their operating systems, such as Windows, or their anti-virus software. In these cases, the firewall usually obtain lists of default rules and restrictions from subscription services, and the focus of the filters is on Internet security and not on filtering Web access in terms of content. - There are two types of firewalls: software firewalls and hardware firewalls. Software firewalls are more common and are often included in operating system software. Freeware firewall programs can be easily downloaded from the Web and installed on any computer. Filtering rules and other settings are usually controlled through a simple, user-friendly software interface. Hardware firewalls are physical computer components that are connected to computers via Ethernet cables. Hardware firewalls are often built into routers for the sake of convenience. In this setup, a computer is connected to a firewall router with an Ethernet cable, and the firewall router is connected to a modem with another Ethernet cable. The modem is then connected to a cable or phone jack, giving it access to the Internet. Settings for the hardware firewall are typically changed via the Web using any Web browser. Hardware firewalls are generally considered to be the most secure types of firewalls available, although the best software-based firewalls come close.
