Stateful multilayer inspection (SMLI) firewalls provide a robust security mechanism that combines the features of both packet filtering and application-based filtering. They are capable of inspecting the state of active connections and make decisions based on the context of the traffic. Cisco Adaptive Security Appliances (ASA) utilize this technology to offer an integrated approach to network security, which includes application-aware firewall capabilities, intrusion prevention, and content security services. This technology is particularly effective as it not only looks at the state and attributes of the packets but also examines the data within the packet, enabling it to provide more comprehensive protection against various types of network threats.
References: The information about the use of stateful multilayer inspection in Cisco ASA is supported by Cisco's official documentation, which outlines the capabilities of the ASA series and its use of SMLI to deliver a powerful multifunction network security appliance family that provides security breadth, precision, and depth for protecting business networks of all sizes123.