The Internet of today is in stark contrast to the close-knit group of research network the made up the Internet forty year ago.As the internet has grown, the need to protect networks and even individual com-
puters has become a major concern. To this.end, devices and software that fall under the banner of firewall have become a necessity for any and all computers connected to the internet that the user wants to remain safe. While the term firewall may conjure different images for different peiple, the basic concept of a firewall is simple: Keep the bad people out of our computer. In this section, explore the
concept of firewalls, what they really do,.and how they do it.

History Lesson

The internet turned forty years old in   2009, but the use of devices to separate one network from another, undesirable network, did not occur until the late 1980s. At the time, network administrators used network routers to prevent traffic from one
network from interfering with the traffic of a neighboring network. Enhanced routers introduced in the 1990s included filtering rules. The designers of these routers designated the device as security firewalls.The configuration of these special routers
prevents unnecessary or unwanted traffic from entering a company’s network boundaries. The routers used filtering rules to determine which network network traffic administration considered good and
which traffic they considered bad, but the use of router filtering rules was cumbersome to maintain as networks continued to evolve.

The next generation of security firewalls improved on these filter enabled routers. During the early 1990s, companies such as DEC, Check point, and Bell Labs developed new features for firewalls.check point, for instance, eased the technical expertise requirement for configuring firewalls by providing user-friendly interfaces while at the same time providing
administrators with new configuration options fof refined rule sets.

What is in a Name??

The question remains: what exactly is a firewall?? Firewalls are network devices or software that separate one trusted network from an untrusted network by means of rule based filtering of network traffic as depicted in this picture. Despite the broad 
definition of a firewall, the specifics of
what makes up a firewall depend on the type of firewall. There are three basic types of a firewall: packet filtering firewalls, stateful firewalls, and application gateway firewalls, while each of these different fire-
wall types performs the same basic operation of filtering undesirable traffic, they go about the task in different manners and at different levels of the network stack.

While identifies the firewall as a  separate physical device at the boundary between an untrusted nd trusted network, in reality a firewall is merely software.this.doesn’t mean that physical, separate device are not firewalls, but merely that these device are simply computers running fire-
wall software. Host-based firewalls have found thier way into most operating sys.. . Windows XP and later versions have a built in firewall called the windows Firewall functionality; therefore,it’s important to understand that firewalls can exist at different locations within a network, not just at the perimeter of a network.