 Wireshark, and the other programs distributed with it such as TShark, are free software, released under the terms of the GNU General Public License.Wireshark is very similar to tcpdump, but has a graphical front-end, plus some integrated sorting and filtering options.Wireshark lets the user put network interface controllers into promiscuous mode (if supported by the network interface controller), so they can see all the traffic visible on that interface including unicast traffic not sent to that network interface controller's MAC address.