Ethereal Network Analyzer
Ethereal is a network protocol analyzer that enables you to capture and examine data from a live network or from a capture file on disk. You can interactively browse the capture data and view summary and detail information for each packet. Ethereal has several powerful features, including a rich display filter language and the ability to view the reconstructed stream of a TCP session. It can read capture files from tcpdump (libpcap), NAI Sniffer (compressed and uncompressed), Sniffer Pro, NetXray, snoop, Shomiti Surveyor, AIX's iptrace, Microsoft Network Monitor, Novell's LANalyzer, RADCOM's WAN/LAN Analyzer, HP-UX nettl, ISDN4BSD, Cisco Secure IDS iplog, the pppd log (pppdump-format), and the AG Group s/Wildpacket's Etherpeek. It can also read traces made from Lucent/Ascend WAN routers and Toshiba ISDN routers. Any of these files can be compressed with gzip and Ethereal will decompress them on the fly.
The license of this software is Freeware, you can free download and free use this protocol analyzer software.