What is two layer DDoS protecton?

The Open Systems Interconnection (OSI) model defines seven conceptual layers in a communications network. DDoS attacks mainly exploit three of these layers:
network (layer 3), transport (layer 4), and application (layer 7). Network (Layer 3/4) DDoS Attacks: The majority of DDoS attacks target the network and transport layers. Such attacks occur when the number of data packets and other traffic overloads a network or server and consumes all of its available resources. Application (Layer 7) DDoS Attacks: Breach or vulnerability in a web application. The perpetrators overwhelm the server or database powering a web application by exploiting it, bringing it to its knees. Such attacks mimic legitimate user traffic, making them harder to detect.