zmap (network scanner)

ZMap is a fast network scanner designed for Internet-wide network
surveys. On a typical desktop computer with a gigabit Ethernet connection,
ZMap is capable scanning the entire public IPv4 address space in under
five minutes.

ZMap can be used to study protocol adoption over time, monitor service
availability and help us better understand large systems distributed
across the Internet.

WARNING: While ZMap is a powerful tool for researchers, please keep
in mind that by running ZMap, you are potentially scanning the ENTIRE
IPv4 address space and some users may not appreciate your scanning.
We encourage ZMap users to respect requests to stop scanning and to
exclude these networks from ongoing scanning.