masscan is a high-performance network port scanner capable of scanning the entire IPv4 Internet in under 5 minutes. Unlike typical scanners, it implements a custom TCP/IP stack to avoid kernel overhead, uses randomized probe ordering via a Feistel cipher (BlackRock) for stealth, and supports both IPv4 and IPv6. The scanner is architecturally a multithreaded C application with separate transmit and receive threads per network adapter, a lock-free ring buffer for inter-thread communication, and a plugin system for output formats (XML, JSON, binary, Redis) and protocol parsers (HTTP, SSH, SSL, SMB, etc.). Key entry points include main.c (initialization), main-conf.c (configuration), transmit_thread() (probe generation), and receive_thread() (response handling). External dependencies are minimal: libpcap (loaded dynamically) for raw packet I/O, and optional PF_RING for higher throughput. Lua scripting is also supported for custom extensions.