The Cisco Secure PIX Firewall 535 delivers carrier-class performance that meets the needs of large enterprise networks as well as service providers. As part of the world-leading Cisco Secure PIX Firewall series, it provides today's networking customers with unmatched security, reliability, and performance. The PIX 535 integrates stateful firewall and IP Security (IPsec) virtual private network (VPN) functionality with Gigabit Ethernet throughput. The PIX 535 is a purpose-built firewall appliance that offers an unprecedented level of protection. This is tightly integrated with the PIX Operating System (OS), which is a proprietary, hardened system that eliminates security holes and performance degrading overhead. At the heart of this system is a protection scheme based on the Adaptive Security Algorithm (ASA), which offers stateful connection-oriented firewalling that is capable of 500, 000 concurrent connections while at the same time blocking common denial of service (Dos) attacks. The PIX 535 is also a full-featured VPN gateway that can securely transport data over public networks. It supports both site-to-site and remote access VPN applications via 56-bit Data Encryption Standard (DES) or 168-bit 3DES. The integrated VPN functionality of the PIX 535 can be supplemented with an optional VPN Accelerator Card (VAC) to deliver 100 Mbps throughput and 2, 000 IPsec tunnels.