Wireshark is a free packet sniffer computer application. It is used for network troubleshooting, analysis, software and communications protocol development, and education. In June 2006 the project was renamed from Ethereal due to trademark issues.
The functionality Wireshark provides is very similar to tcpdump, but it has a graphical front-end, and many more information sorting and filtering options. It allows the user to see all traffic being passed over the network (usually an Ethernet network but support is being added for others) by putting the network interface into promiscuous mode.
Wireshark uses the cross-platform GTK+ widget toolkit, and is cross-platform, running on various computer operating systems including Linux, Mac OS X, and Microsoft Windows. Released under the terms of the GNU General Public License.
Wireshark 2.1 User's Guide
Wireshark 1.4 User's Guide
Wireshark 1.4 Developer's Guide
Wireshark 1.2 User's Guide
Wireshark 1.2 Developer's Guide
Wireshark 1.0.0 User's Guide
Wireshark 1.0.0 Developer's Guide
Wireshark @ Sourceforge