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 available source codes, such general-purpose operating systems provide less-than-optimum performance and security. The dedicated Cisco Secure PIX Firewall series is designed specifically for secure, high-performance protection. The Cisco Secure PIX Firewall 506 is part of the world-leading Cisco Secure PIX Firewall series, providing today's networking customers with unmatched security, reliability, and performance. It delivers full firewall protection, as well as IP Security (IPsec) Virtual Private Network (VPN) capabilities, which allows you to rigorously protect your internal network from the outside world. The Cisco Secure PIX Firewall 506 is designed for companies that are leveraging the cost advantages of the Internet and allowing employees to work remotely. It specifically targets organizations where engineers, developers and other so-called "power users" are maintaining multiple computers that connect back into the corporate network through Internet Service Providers (ISPs) or VPNs.