An ethical hacker is preparing to scan a network to identify live systems. To increase the efficiency and accuracy of his scans, he is considering several different host discovery techniques. He expec

ICMP ECHO Ping Sweep is often blocked by restrictive firewalls, as administrators frequently configure firewalls to drop ICMP Echo requests to prevent network reconnaissance and denial-of-service attacks.

ICMP Timestamp Ping, like other ICMP types, is commonly filtered by restrictive firewalls to limit information leakage and prevent reconnaissance attempts that could identify system uptime or time synchronization.

TCP SYN Ping can be used for host discovery, but if the specific TCP port targeted by the SYN packet is closed or heavily filtered by a restrictive firewall, the host may appear inactive even if it is live.

ARP Ping Scan is highly effective for discovering active hosts on a local area network because it operates at Layer 2 (Data Link Layer). Firewalls primarily filter traffic at Layer 3 (Network Layer) and Layer 4 (Transport Layer), meaning ARP requests typically bypass these higher-layer security controls, even for systems with restrictive firewalls configured to block ICMP or specific TCP ports.