Which layer of the OSI model do firewalls primarily operate on?

Firewalls primarily operate at Layer 3 and Layer 4 of the OSI model because these layers deal with network and transport protocols, which are crucial for filtering and controlling data flow. Layer 3, the Network layer, is responsible for routing packets through the network and managing IP addressing. Firewalls analyze incoming and outgoing network traffic based on IP addresses and protocol types at this layer to determine whether to allow or block traffic.

Layer 4, the Transport layer, manages the end-to-end communication and handles the segmentation of data streams. Here, firewalls filter traffic based on transport protocols, such as TCP or UDP, and their respective port numbers. By examining this information, firewalls can enforce rules and policies related to specific services and applications.

In contrast, Layer 1 and 2 are primarily focused on physical connections and data link protocols, while Layer 6 and 7 pertain to presentation and application layers where data formatting and application-level communication occur. Firewalls do not typically function at those higher layers, which are more concerned with user applications and data representation rather than network traffic control.