Which firewall technology operates at Layer 3 by comparing packet headers to ACLs to determine which traffic to accept?

Which firewall technology operates at Layer 3 by comparing packet headers to ACLs to determine which traffic to accept?

• A. Stateful inspection
• B. Layer 7 firewall
• C. Packet filtering firewall
• D. Layer 4 firewall

Answer: (C)

Focusing on filtering at the network layer, a packet filtering firewall makes decisions by inspecting the IP header fields—such as source and destination addresses and the protocol—and comparing them against a set of access control list rules. If the header matches an allow rule, the packet is permitted; if it matches a deny rule, it’s blocked. This stateless, header-based approach is exactly what happens at Layer 3, where the firewall doesn’t look into the payload or maintain any connection state. The other options describe different capabilities: a stateful inspection firewall keeps track of ongoing connections and uses history to make decisions; a Layer 7 firewall examines application-layer data to enforce rules based on content; a Layer 4 firewall focuses on transport-layer information like port numbers and protocols, which goes beyond the simple header comparisons used at Layer 3. Since the scenario specifies Layer 3 header-based ACL matching, the packet filtering firewall is the best fit.

Focusing on filtering at the network layer, a packet filtering firewall makes decisions by inspecting the IP header fields—such as source and destination addresses and the protocol—and comparing them against a set of access control list rules. If the header matches an allow rule, the packet is permitted; if it matches a deny rule, it’s blocked. This stateless, header-based approach is exactly what happens at Layer 3, where the firewall doesn’t look into the payload or maintain any connection state.

The other options describe different capabilities: a stateful inspection firewall keeps track of ongoing connections and uses history to make decisions; a Layer 7 firewall examines application-layer data to enforce rules based on content; a Layer 4 firewall focuses on transport-layer information like port numbers and protocols, which goes beyond the simple header comparisons used at Layer 3. Since the scenario specifies Layer 3 header-based ACL matching, the packet filtering firewall is the best fit.