Which scan relies on analyzing the TTL field value of RST packets in response to ACK probes?

Which scan relies on analyzing the TTL field value of RST packets in response to ACK probes?

• A. ACK Flag Probe Scan
• B. TTL-Based ACK Flag Probing Scanning
• C. Window-Based ACK Flag Probing Scanning
• D. IDLE/IPID Header Scan

Answer: (B)

The idea being tested is using the TTL field in TCP responses as a fingerprinting signal when probing a host with ACK packets. In this approach, you send ACK probes to a target and then look at the TTL value in the RST packets that the host returns (or at whether a response is received at all). The TTL in those RST responses is tied to the initial TTL that the host uses when sending packets (which varies by operating system) and how many hops the packet has traversed. By analyzing those TTL values, you can infer characteristics about the replying host—often to identify the OS family or to distinguish between a host that’s responding versus one that’s filtering traffic. This technique is distinct from scans that rely on whether an ACK probe elicits a response, or on other header fields like the TCP window size or the IPID, because it centers on the TTL value of the RST reply itself as the clue. If the TTLs in the RST responses align with certain known initial TTL defaults, you gain useful information about the target’s behavior and identity, which is the essence of TTL-Based ACK Flag Probing Scanning.

The idea being tested is using the TTL field in TCP responses as a fingerprinting signal when probing a host with ACK packets. In this approach, you send ACK probes to a target and then look at the TTL value in the RST packets that the host returns (or at whether a response is received at all). The TTL in those RST responses is tied to the initial TTL that the host uses when sending packets (which varies by operating system) and how many hops the packet has traversed. By analyzing those TTL values, you can infer characteristics about the replying host—often to identify the OS family or to distinguish between a host that’s responding versus one that’s filtering traffic.

This technique is distinct from scans that rely on whether an ACK probe elicits a response, or on other header fields like the TCP window size or the IPID, because it centers on the TTL value of the RST reply itself as the clue. If the TTLs in the RST responses align with certain known initial TTL defaults, you gain useful information about the target’s behavior and identity, which is the essence of TTL-Based ACK Flag Probing Scanning.