What is a Firewall?
A. A firewall is a system or group of systems that enforces an access control policy between two networks. The actual means by which this is accomplished varies widely, but in principle, the firewall can be thought of as a pair of mechanisms: one which exists to block traffic, and the other which exists to permit traffic. Some firewalls place a greater emphasis on blocking traffic, while others emphasize permitting traffic. Probably the most important thing to recognize about a firewall is that it implements an access control policy. If you don’t have a good idea what kind of access you want to permit or deny, or you simply permit someone or some product to configure a firewall based on what they or it think it should do, then they are making policy for your organization as a whole.
Afirewall is a security mechanism which provides controlled access to the information stored on the computer. It is implemented through a combination of hardware and software that may filter access requests in either direction. For example, an outside user requesting access to product specification on the web site can be allowed access via an authorization procedure but will not be allowed access to other information (e.g., sales data).
The Firewalls FAQ (http://www.faqs.org/faqs/firewalls-faq/) defines a firewall as “a system or group of systems that enforces an access control policy between two networks.” In the context of home networks, a firewall typically takes one of two forms: Software firewall – specialized software running on an individual computer, or Network firewall – a dedicated device designed to protect one or more computers. Both types of firewall allow the user to define access policies for inbound connections to the computers they are protecting. Many also provide the ability to control what services (ports) the protected computers are able to access on the Internet (outbound access). Most firewalls intended for home use come with pre-configured security policies from which the user chooses, and some allow the user to customize these policies for their specific needs.
A firewall is a system deployed between two or more networks to enforce an access control policy between them, that is to say it can allow certain types of traffic between them and block other types of traffic. It goes without saying that if you have no idea which traffic to allow or deny a firewall will not be of real help to you. It is also important to be aware of how to configure the firewall and the outcomes of these configurations. Therefore, firewall administrators with large number of network nodes have a huge responsibility to attend to.
