Analyze and troubleshoot your network with Wireshark
 

Wireshark is a free packet analyzer computer application. It is used for network troubleshooting, analysis, software and communications protocol development, and education. Originally named Ethereal, in May 2006 the project was renamed Wireshark due to trademark issues. Wireshark is cross-platform, using the GTK+ widget toolkit to implement its user interface, and using pcap to capture packets. It’s free of cost.

It can serve deep inspection of hundreds of protocols and can perform live capture and offline analysis. It can track and monitor packets (IP, TCP, UDP). It runs on Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and many others. It can also monitor live stream of data.