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 more than a thousand 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.

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