Wireshark

Wireshark is a network packet analyzer.

The Ethereal network protocol analyzer has changed its name to Wireshark.

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.

http://www.wireshark.org/