Wireshark.org - (Free)
Wireshark helps network administrators to solve protocol issues by diagnosing the problems in the software protocols.
Wireshark is a famous network analysis or packet sniffer tool protocols.
Wireshark examine data from a live network, and can also take a snapshot of the various communications that work on it at another time. Wireshark proposes to see the "dissector tables" directly from the main window. The application can export objects to SMB screen or display the compiled BPF code for capture filters. Finally, Wireshark supports a variety of protocols such as ADwin, Apache Etch, JSON, reload or Wi-Fi P2P (Wi-Fi Direct).
The interface is quite austere, hides an extremely powerful that only experts can use software correctly.
This software is essential for any network administrator to diagnose problems in the software protocols.