The purpose of establishing perimeter security for networks is to enable organizations to manage the risks associated with connecting proprietary enterprise networks to one or more external entities via private or public networks. With the deliberate and complex integration of networks among organizations, simple barriers are no longer appropriate or adequate solutions to network security. Network perimeter security is an organization’s first and most important layer of defense. A key concept of security is depth—multiple layers of defense that have to be circumvented to gain access to internal information assets and resources.