Wireshark is the world's foremost network protocol analyzer, and is the standard in many industries. It is the continuation of a project that started in 1998. Features includes deep inspection of hundreds of protocols, with more being added all the time, Live capture and offline analysis, Standard three-pane packet browser, Captured network data can be browsed via a GUI, or via the TTY-mode TShark utility, and Rich VoIP analysis.
