Wireshark (previously Ethereal) is the world's foremost network protocol analyzer, and is the standard in many industries.
It is the continuation of a project that started in 1998. Hundreds of developers around the world have contributed to it, and it is still under active development.
Wireshark has a rich feature set which includes the following:
* Hundreds of protocols are supported, with more being added all the time * Live capture and offline analysis are supported * Standard three-pane packet browser * Multi-platform: Runs on Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and many others * Captured network data can be browsed via a GUI, or via the TTY-mode TShark utility * The most powerful display filters in the industry * Rich VoIP analysis * Read/write many different capture file formats: tcpdump (libpcap), Catapult DCT2000, Cisco Secure IDS iplog, Microsoft Network Monitor, Network General Sniffer® (compressed and uncompressed), Sniffer® Pro, and NetXray®, Network Instruments Observer, Novell LANalyzer, RADCOM WAN/LAN Analyzer, Shomiti/Finisar Surveyor, Tektronix K12xx, Visual Networks Visual UpTime, WildPackets EtherPeek/TokenPeek/AiroPeek, and many others * Capture files compressed with gzip can be decompressed on the fly * Live data can be read from Ethernet, IEEE 802.11, PPP/HDLC, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others (depending on your platfrom) * Decryption support for many protocols, including IPsec, ISAKMP, Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2 * Coloring rules can be applied to the packet list, which eases analysis * Output can be exported to XML, PostScript®, CSV, or plain text
