CompTIA: Advanced Security Practitioner (CASP) Exam Prep

Answer: C - A packet-filtering firewall functions at the network layer of the OSI model.

Key Takeaway: A packet-filtering firewall examines the source IP address, source port, destination IP address, destination port, and the IP protocol, whether TCP or UDP. Depending on the rules configured on the firewall, the packet will be allowed through, rejected, or dropped. If the firewall rejects the packet, it sends a message back to the sender letting him know that the packet was rejected. If the packet was dropped, the firewall simply does not respond to the packet. The sender must wait for the communication to time out. Dropping packets instead of rejecting them greatly increases the time required to scan your network. Packet filtering firewalls operate on layer 3 of the OSI model, the network layer.