Rachel is using the Ping method for sniffer detection. The distinguishing behavior in the scenario is that she sends ICMP echo requests (pings) crafted so that the Layer 2 MAC address is incorrect/mismatched, while the Layer 3 IP destination is correct. Under normal circumstances, a host’s network interface card (NIC) should drop frames not addressed to its MAC address. However, when a NIC is set to promiscuous mode (as sniffers often require), it can accept frames regardless of destination MAC and pass them up the stack. If the operating system then processes the encapsulated IP packet and responds (e.g., sends an ICMP echo reply), that response suggests the host is accepting frames it normally would ignore—an indicator consistent with promiscuous mode sniffing.
This technique is used as a heuristic: by intentionally violating normal Ethernet delivery rules and observing whether the target still responds, you can infer that the interface may be capturing traffic not explicitly addressed to it. It’s not perfect—modern drivers, switches, VLAN configurations, and host firewall behavior can affect results—but the scenario’s “mismatched MAC but correct IP” plus “the suspected machine responds” is the classic signature of the ping-based promiscuous-mode test.
Why the other options are less suitable:
ARP method (B) typically involves ARP-based tricks (non-broadcast ARP requests or crafted ARP traffic) to test how the target responds; the scenario explicitly describes ICMP behavior.
DNS method (C) relates to DNS queries/resolution behavior and does not match the ICMP/MAC mismatch test.
Nmap sniffer-detect (NSE) (D) is a specific scripted approach, but the question asks for the underlying technique being used; the described action matches the Ping method.
Therefore, the correct answer is A. Ping Method.
