Ethereal

This application is what people usually call a "Sniffer". You can use Ethereal to monitor network traffic. That will help you analyze network problems, detect intrusion attempts, Monitor usage, collect statistics, filter content from network traffic, debug communications. This program has all the standard features expected in a protocol analyzer, and some features you won't find in other products. It runs on all the major operating systems including Unix, Linux, and Windows. Some protocols you can monitor with Ethereal are: FTP, SIP, G723, DTP, PPP, RMI, RMP, RTP, SCCP, among hundreds of others. If you are familiar with networking and protocols, are a network administrator, or a student interested in packet sniffing, Ethereal will be a good choice. Note: Since June 2006 Ethereal became Wireshark, with a new home and different download pages. Wireshark has continued to improve Ethereal and added new features that keep it as one of the best options when talking about packet analysis, it works with new platforms like Windows Vista.