WireShark
Wireshark (previously known as Ethereal) is a open source network protocol analyzer that runs on both Unix and Windows.
Wireshark is used to capture or to examine data live on a network .
Features:
- Rrich display filter language
- Ability to view the reconstructed stream of a TCP session
- See network data and packages live.
- Capture network traffic and save to a file
- supports hundreds of protocols and media types.
- A tcpdump-like console version named tethereal