Which technique determines which ports are open and if the packets can pass through the packet filter and the firewall?

• A. Port Scanning
• B. Firewalking
• C. Packet Filtering
• D. Deep Packet Inspection

Answer: (B)

Firewalking is a probing technique used to map what traffic is allowed through a firewall or ACL. By sending packets toward a target with carefully chosen TTL values and observing the responses (or the lack of responses) from the next hop, you can infer which protocols and ports are permitted to pass through the firewall. This lets you determine which ports behind the firewall are effectively reachable and which are blocked, revealing how the firewall rules shape traffic flow.

Port scanning, by contrast, shows which ports are open on a specific host, but doesn’t tell you how firewall rules affect reachability from outside. Deep packet inspection focuses on the content of packets to enforce policies, not on discovering reachability through a firewall. Packet filtering refers to the firewall’s function itself rather than a discovery technique.