It is the de facto (and often de jure) standard across many industries and educational institutions. Wireshark development thrives thanks to the contributions of networking experts across the globe. It is the continuation of a project that started in 1998. Wireshark was written by networking experts around the world, and is an example of the power of open source. Wireshark is used by network professionals around the world for analysis, troubleshooting, software and protocol development and education. The program has all of the standard features you would expect in a protocol analyzer, and several features not seen in any other product. Its open source license allows talented experts in the networking community to add enhancements.

Features:

• Data can be captured "off the wire" from a live network connection, or read from a capture file.
• Wireshark can read capture files from tcpdump (libpcap), NAI's Sniffer (compressed and uncompressed), Sniffer Pro, NetXray, Sun snoop and atmsnoop, Shomiti/Finisar Surveyor, AIX's iptrace, Microsoft's Network Monitor, Novell's LANalyzer, RADCOM's WAN/LAN Analyzer, HPUX nettl, i4btrace from the ISDN4BSD project, Cisco Secure IDS iplog, the pppd log (pppdumpformat), the AG Group's/WildPacket's EtherPeek/TokenPeek/AiroPeek, or Visual Networks' Visual UpTime. It can also read traces made from Lucent/Ascend WAN routers and Toshiba ISDN routers, as well as the text output from VMS's TCPIPtrace utility and the DBS Etherwatch utility for VMS. Any of these files can be compressed with gzip and Ethereal will decompress them on the fly.
• Live data can be read from Ethernet, FDDI, PPP, Token*Ring, IEEE 802.11, Classical IP over ATM, and loopback interfaces (at least on some platforms; not all of those types are supported on all platforms).
• Captured network data can be browsed via a GUI, or via the TTY*mode "tethereal" program.
• Capture files can be programmatically edited or converted via command*line switches to the "editcap" program.
• 602 protocols can currently be dissected
• Output can be saved or printed as plain text or PostScript.
• Data display can be refined using a display filter.
• Display filters can also be used to selectively highlight and color packet summary information.
• All or part of each captured network trace can be saved to disk.