<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules . A firewall typically establishes a barrier between a trusted internal network and untrusted external network, such as the Internet . </P> <P> Firewalls are often categorized as either network firewalls or host - based firewalls . Network firewalls filter traffic between two or more networks and run on network hardware . Host - based firewalls run on host computers and control network traffic in and out of those machines . </P>

Fire wall is used in communication to save from