In the security strategy of networks, the firewall has become a key ingredient in safeguarding network integrity. A firewall is the default security module that prevents data packets from either entering or leaving a specified network. It can be hardware as well as software-based. It monitors and controls the incoming and outgoing network traffic based on predetermined security rules. It basically acts as a barrier between a trusted, secure internal network and another outside network. The perimeter network protects your intranet or enterprise local area network (LAN) from intrusion by controlling access from the Internet or other large networks. A perimeter network is sometimes referred to as the demilitarized zone (DMZ). The following diagram clearly illustrates the concept of network security:
