Masscan is a TCP port scanner that transmits packets asynchronously to scan large address ranges at extreme speed.
Masscan solves the problem of scanning large networks or the entire Internet by using asynchronous transmission rather than waiting for responses between probes. It implements its own ad hoc TCP/IP stack to achieve rates of millions of packets per second from a single machine. The tool accepts parameters similar to nmap, supporting arbitrary port and address ranges, and can output results to stdout for further processing.
Masscan suits operators who need to scan many machines across broad network ranges rather than perform deep inspection of individual hosts. Its speed makes it practical for Internet-scale reconnaissance, but this comes with a significant operational constraint: because it uses its own TCP/IP stack, it can conflict with the local stack unless you configure it to use different source IP addresses or source ports and firewall those ports away from the operating system. The README notes that features supporting widespread scanning are prioritized, while in-depth single-machine scanning is not. The tool also supports banner checking across multiple protocols including HTTP, SSH, SSL, FTP, SMTP, and others, allowing basic service identification beyond simple port detection.
The project maintains a straightforward build process with minimal dependencies beyond a C compiler, and the codebase compiles on Linux, macOS, Windows, and FreeBSD with platform-specific build instructions provided. Development activity shows ongoing maintenance with attention to cross-platform compatibility and operational usability.
