Wireshark

Wireshark allows you to examine protocol data stored in files or as it

is captured from wired or wireless (WiFi or Bluetooth) networks, USB

devices, and many other sources. It supports dozens of protocol

capture file formats and understands thousands of protocols.

It has many powerful features including a rich display filter language

and the ability to reassemble multiple protocol packets in order to,

for example, view a complete TCP stream, save the contents of a file

which was transferred over HTTP or CIFS, or play back an RTP audio

stream.