Wireshark is designed as a free network protocol analyzer intended for Windows and Unix platforms. This is an accurate and highly reliable software for network troubleshooting and protocol development. Intended for network professionals, this protocol analyzer comes with all the standard features. Wireshark comes as an open source software which allows talented experts in the networking community to add enhancements.
Wireshark is jam-packed with the following features:

• Data can be captured "off the wire " from a live network connection
• 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, HP-UX nettl, i4btrace from the ISDN4BSD project, Cisco Secure IDS iplog, the pppd log (pppdump-format), the AG Group's/WildPacket's EtherPeek/TokenPeek/AiroPeek, or Visual Networks' Visual UpTime
• 602 protocols can be dissected
• output can be saved or printed as plain text as PostScript
System requirements:
WinPcap 4.x installation