Wireshark's powerful features make it the tool of choice for network troubleshooting, protocol development, and education worldwide.
Wireshark was written by an international group of networking experts, and is an example of the power of open source. It runs on Windows, Linux, UNIX, and other platforms.
It used to be known as Ethereal, and was renamed in May 2006.
Wireshark Packet Sniffer - formerly known as Ethereal - is a must-have tool for every Network Engineer, but these guys have got a cool OUI Lookup tool on their site as well.
