At which layer of the OSI model do packet filtering firewalls operate?

Packet filtering firewalls operate at the network layer of the OSI model, which is the third layer. They inspect the headers of packets and determine whether to allow or block them based on predetermined security rules. The network layer is responsible for the routing of data packets between devices on different networks, and packet filtering addresses the flow of data based on IP addresses, protocols, and port numbers.

This layer allows the firewall to effectively manage traffic and enforce security policies that specify which devices can communicate with each other over a network. By utilizing this layer, packet filtering firewalls can handle a wide range of protocols, providing a basic level of security without needing to analyze the contents of the packets, which would occur at higher layers such as the transport or application layers.