Wireshark
Wireshark is a free and open source packet analyzer. It is used for network troubleshooting, analysis, software and communication protocol development, as well as training and education.
It is among the most popular packet analyzers available. Initially released in 1998, It has continually evolved and has been continually upgraded and has developed into one of the most powerful and useful network troubleshooting tools available.
Wireshark is most often used in conjunction with switch features such as SPAN to capture and analyze traffic.
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