Penetration testing is a method of evaluating the security of a system or network by simulating an attack from a malicious source. Penetration testing typically consists of four phases: planning, discovery, attacks, and reporting. In the discovery phase, penetration testers gather information about the target system or network, such as host detection, domain name system (DNS) interrogation, port scanning, service identification, operating system fingerprinting, vulnerability scanning, etc. This information can help to identify potential entry points, weaknesses, or vulnerabilities that can be exploited in the subsequent attack phase. Host detection and DNS interrogation are techniques that can be used in the discovery phase to determine the active hosts and their IP addresses and hostnames on the target network. References: [ISACA CISA Review Manual 27th Edition], page 368.