A Certified Ethical Hacker (CEH) is analyzing a target network. To do this, he decides to utilize an IDLE/IPID header scan using Nmap. The network analysis reveals that the IPID number increases by…

While an IPID increment of 2 typically indicates an open port, option D provides a more specific conclusion about the network's underlying security infrastructure, which is a key objective for a Certified Ethical Hacker.

An open port does not imply the absence of a firewall; a firewall can be present but configured to permit traffic to that specific port.

An IPID increment of 2 explicitly signifies an open port according to the Nmap IDLE scan methodology, as a closed or filtered port would result in an IPID increment of only 1.

The predictable IPID increment of 2 observed on the zombie host, which results from an open target port, indicates that the spoofed connection attempt and subsequent responses are being tracked. A stateful firewall maintains a state table for active connections, allowing the SYN, SYN/ACK, and RST packets involved in this specific IDLE scan interaction to traverse the network in a consistent manner, enabling the reliable observation of the IPID increment.