The Cisco Secure PIX Firewall offers an unprecedented level of security protection. At the heart is a protection scheme based on Adaptive Security Algorithm (ASA), which offers stateful connection-oriented firewalling. Stateful security is less complex and more robust than packet filtering. It also offers higher performance and is more scalable than application-level proxy firewalls. ASA tracks the source and destination address, Transmission Control Protocol (TCP) sequence numbers, port numbers, and additional TCP flags of each packet. Access is permitted through the Cisco Secure PIX Firewall series only if an appropriate connection exists to validate passage. This gives organizations transparent access for internal and authorized external users, while protecting internal networks from unauthorized access. The real-time embedded system also enhances the security of the Cisco Secure PIX Firewall series. Although UNIX servers are ideal open-development platforms with widely availabl...