Wireshark network packet analyzer
Wireshark is a free network packet analyzer. It will try to capture network packets and tries to display that packet data as detailed as possible.
You could think of a network packet analyzer as a measuring device used to examine what’s going on inside a network cable, just like a voltmeter is used by an electrician to examine what’s going on inside an electric cable (but at a higher level, of course).
You can use Wireshark to troubleshoot network problems, examine security problems, debug protocol implementations, learn network protocol internals.
Features: Available for UNIX and Windows., Capture live packet data from a network interface., Display packets with very detailed protocol information., Open and Save packet data captured., Import and Export packet data from and to a lot of other capture programs., Filter packets on many criteria., Search for packets on many criteria., Colorize packet display based on filters., Create various statistics., and more!