masscan

masscan -p1-65535 <cidr> --rate=10000

High-speed port scanner that can sweep the entire internet in minutes.

When you need to scan large IP ranges (e.g., /16 or /8) in a short time. In an engagement where the client wants a quick inventory of exposed services, masscan is unbeatable. Also useful for discovering open ports before launching nmap with scripts.

If stealth is a priority, masscan is very noisy. Also if the target has IDS/IPS that detect high-speed scans. Prefer nmap with slow timing for stealthy tests.