A TCPDump is a freeware protocol analyzer for Unix systems that can monitor network traffic on a wire. It allows the user to display TCP/IP and other packets being transmitted or received over a network. Tcpdump works on most Unix-like operating systems: Linux, Solaris, BSD, OS X, HP-UX, Android and AIX among others. It was originally written in 1987 by Van Jacobson, Craig Leres and Steven McCanne who were working in the Lawrence Berkeley Laboratory Network Research Group