Networking Device and Protocols

7.3. Firewalls operate at the following layers

OSI Model
In the OSI model, firewalls operate at the following layers:

Network Layer (Layer 3): Firewalls can filter traffic based on source and destination IP addresses

Transport Layer (Layer 4): Firewalls can filter traffic based on source and destination port numbers

TCP/IP Model
In the TCP/IP model, firewalls operate at the following layers:

Internet Layer (equivalent to OSI Layer 3): Firewalls can filter traffic based on source and destination IP addresses

Transport Layer (equivalent to OSI Layer 4): Firewalls can filter traffic based on source and destination port numbers

In summary, firewalls are critical network security devices that control and monitor network traffic, protecting networks from unauthorized access and malicious attacks. They operate at the network and transport layers of both the OSI and TCP/IP models.