Masscan

Masscan is the fastest Internet-scale port scanner, capable of scanning the entire IPv4 address space (all 4 billion addresses) in under 6 minutes when run from a single machine with a 10 Gbps network connection. Created by Robert David Graham, it achieves this extraordinary speed by using a custom TCP/IP stack implemented entirely in userspace (via raw sockets), bypassing the operating system network stack entirely. This design allows Masscan to transmit up to 10 million packets per second, compared to Nmap which typically sends a few thousand packets per second. Masscan performs asynchronous scanning: it sends SYN packets and processes responses independently, maintaining a state machine for tracking outstanding probes. Key features include: TCP port scanning (SYN scan), UDP port scanning, banner grabbing on common ports (HTTP, SSH, FTP, SMTP, SSL certificates), custom TCP/IP stack with source IP spoofing support, configurable transmission rate (packets per second), random target and port ordering (to spread load across networks), output formats (XML, binary, JSON, grepable, list), and Lua scripting for custom banner parsing. Masscan was designed with security research in mind and includes features for scanning the entire Internet to track exposed services. As of 2026, it has over 25,800 stars.