hping3

root@mybox: # hping3 -A 192.168.2.x -p 80

Hping is a great tool that provides a variety of options. You can craft packets with it, audit and test firewalls, and do all sorts of crazy man-in-the-middle stuff with it. In this example, you’re simply performing a basic ACK scan (the -A switch) using port 80 (-p 80) on an entire Class C subnet (the x in the address runs through all 254 possibilities). Hping3, the latest version, is scriptable (TCL language) and implements an engine that allows a human-
readable description of TCP/IP packets