Tcpdump

What is tcpdump?
Tcpdump is a type of packet analysis software utility that monitors and logs TCP / IP traffic transmitted between a network and the computer on which it is running.
Tcpdump is an open source network utility that is freely available under the BSD license. Tcpdump works on the command line interface and provides descriptions of the package contents in different formats depending on the command used.

Tcpdump is primarily a network monitoring and management program that collects and records TCP / IP data at runtime. Tcpdump provides statistics on the number of received and recorded packets on the operating node for analyzing network performance, troubleshooting and diagnosing network bottlenecks and other network-oriented tasks.

Because it is a command line utility, the data retrieved through tcpdump can vary. For example, when used with an -A operator, it prints each packet in ASCII format. Tcpdump is supported by most Unix-based operating systems such as Linux, Mac OSX and BSD. The Windows variant of tcpdump is called WinDump.