Wireshark

Wireshark (known as Ethereal until a trademark dispute in Summer 2006) is a fantastic open source multi-platform network protocol analyzer. It allows you to examine data from a live network or from a capture file on disk. You can interactively browse the capture data, delving down into just the level of packet detail you need. Wireshark has several powerful features, including a rich display filter language and the ability to view the reconstructed stream of a TCP session. It also supports hundreds of protocols and media types. A tcpdump-like console version named tshark is included. One word of caution is that Wireshark has suffered from dozens of remotely exploitable security holes, so stay up-to-date and be wary of running it on untrusted or hostile networks (such as security conferences).

Wireshark is the world's foremost network protocol analyzer. It lets you capture and interactively browse the traffic running on a computer network. 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.

Features

Wireshark has a rich feature set which includes the following:

• Deep inspection of hundreds of protocols, with more being added all the time
• Live capture and offline analysis
• 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), Pcap NG, Catapult DCT2000, Cisco Secure IDS iplog, Microsoft Network Monitor, Network General Sniffer® (compressed and uncompressed), Sniffer® Pro, and NetXray®, Network Instruments Observer, NetScreen snoop, 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 platform)
• 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 for quick, intuitive analysis
• Output can be exported to XML, PostScript®, CSV, or plain text
  
  Windows Installer (32-bit)             : Download
  
  Windows Installer (64-bit)                 :Download
  
  Windows U3 (32-bit)                        :Download
  
  Windows PortableApps (32-bit)       :Download
  
  
  

  OS X 10.6 and later Intel 64-bit .dmg   :Download                                      Source Code :Download