link: ZMap: The Internet Scanner | A faster alternative to nmap

ZMap: The Internet Scanner GitHub

ZMap is a fast single packet 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 45 minutes. With a 10gigE connection and PF_RING, ZMap can scan the IPv4 address space in under 5 minutes.

I use this now and again for testing and it's excellent.