What is the primary function of a packet-filtering firewall?

• A. The header of every packet to decide how to treat the packet
• B. The payload of the entire application data
• C. Only the destination address
• D. Only the source address

Answer: (A)

The primary function is to inspect the header of each packet and decide how to treat it based on that header. Packet-filtering firewalls operate at the network/transport layers, using fields in the header such as the source and destination IP addresses, source and destination ports, and the protocol to decide whether to allow or block traffic. They don’t typically analyze the payload, so decisions are based on header information, not on the actual data carried inside the packet. If you only looked at the destination or only the source address, you’d miss important details like which service or port the traffic intends, which is essential for proper filtering.