hping is a command-line oriented TCP/IP packet assembler/analyzer.
The interface is inspired by the ping(8) unix command, but hping
isn't only able to send ICMP echo requests.  It supports TCP, UDP,
ICMP and RAW-IP protocols, has a traceroute mode, the ability to
send files between a covert channel, and many other features.
While hping was mainly used as a security tool in the past, it can
be used in many ways by people that don't care about security to
test networks and hosts.

Homepage:
http://www.hping.org/
