EC-Council Certified Ethical Hacker (CEH) Certification Practice Exam

Passive OS fingerprinting focuses on the information already present in network traffic rather than sending probes. P0f is built for this approach: it passively monitors captured traffic, analyzes characteristics of the remote host’s TCP/IP stack (such as TTL, window size, IPID behavior, TCP options, and timing patterns), and matches those fingerprints against a database to infer the operating system. This makes it the best fit for OS fingerprinting by analyzing network traffic because it does not generate additional traffic or detectable probes, reducing impact on the target and remaining covert. By contrast, the other tools have different primary roles: a packet analyzer like Wireshark captures and lets you inspect traffic, but it doesn’t automatically map those observations to an OS; a netstat command shows current connections and ports rather than fingerprinting the host; and active scanners that produce results, like Nmap, rely on sending crafted probes to elicit responses, which is not analyzing existing traffic.