LibPCAP^[10]

^[10] http://www.tcpdump.org

LibPCAP and the Microsoft Windows-compatible WinPCAP^[11] are freely available, open source, high-level libraries that allow for the easy construction of network capture and analysis tools across both UNIX and Microsoft Windows platforms. Many network protocol analysis tools such as the aforementioned Wireshark are built against this library.

^[11] http://www.tcpdump.org/wpcap.html