Wireshark

Wireshark is the world's most widely-used network protocol analyzer software. With Wireshark you can get a better understanding on what's happening on your network. The software let's you do deep analysis across hundreds of protocols at a microscopic level. Wireshark is free and open-source and has been in active development by contributions from volunteers across the globe since 1998. Today the software is used by commercial and non-profit enterprises, government agencies, and educational institutions.

Wireshark is a free and open source software released under the GNU General Public License version 2.