Which type of firewall primarily filters traffic based on Layer 3 and Layer 4 information?

The correct answer is a stateless firewall, which primarily filters traffic based on Layer 3 (Network Layer) and Layer 4 (Transport Layer) information. Stateless firewalls make filtering decisions based on static criteria such as IP addresses and port numbers. They do not maintain any information about the state of active connections, meaning they evaluate each packet in isolation without considering the context of a connection. This makes them fast and efficient for straightforward filtering tasks.

In contrast, a stateful firewall monitors the state of active connections and can make more informed decisions based on the context of traffic, typically working at a higher layer than just Layers 3 and 4. A next-gen firewall combines traditional firewall capabilities with additional features like deep packet inspection and intrusion detection. A proxy firewall operates at the application layer, acting as an intermediary between users and the external network. Hence, they do not fit the description of primarily filtering based on Layer 3 and Layer 4 information.