Wireshark

Wireshark is the world's most trusted network protocol analyzer, providing deep inspection of hundreds of protocols with live capture and offline analysis capabilities. This free, open-source tool decodes network communications, helping IT professionals, network administrators, and security experts troubleshoot problems, analyze network performance, and detect security threats. Its powerful filtering and search features let you quickly pinpoint specific packets or conversations, while the detailed protocol dissection reveals exactly what's happening across your network infrastructure.