International Journal of Modern Engineering Research (IJMER)
Firewalls are devices or programs that control the flow of network traffic between hosts or networks that employ differing security postures. While firewalls are often discussed in the context of Internet connectivity, they may also have applicability in various other network environments. At one time, most firewalls were deployed at the network perimeters. This provided some measure of protection for internal hosts, but it could not recognize all instances and forms of attacks, and attacks sent from one internal host to another often do not pass through network firewalls. Because of these and other factors network designers now often include firewall functionality at places other than the network perimeter to provide an additional layer of network security.