For NT 3.1, Microsoft purchased a TCP/IP stack from Spider Systems[0]. It's not clear how much of that code was based on BSD's TCP/IP stack. Microsoft wrote the

For NT 3.1, Microsoft purchased a TCP/IP stack from Spider Systems[0]. It's not clear how much of that code was based on BSD's TCP/IP stack. Microsoft wrote their own TCP/IP stack for NT 3.5.[1] Microsoft did leverage BSD code for common network utilities (ping, tracert, ftp, etc.), which still exist in Windows today, although Microsoft's preference is to leverage the "better" equivalent PowerShell cmdlets where available. [0] https://en.wikipedia.org/wiki/Spider_Systems https://en.wikipedia.org/wiki/Spider_Systems [1] https://web.archive.org/web/20151229084950/http://www.kuro5hin.org/story/2001/6/19/05641/7357 https://web.archive.org/web/20151229084950/http://www.kuro5h... EDIT: If you want to hunt for BSD code, try taking a look at NT4[2]. [2] https://github.com/lianthony/NT4.0/tree/master/private/ntos/tdi/tcpip https://github.com/lianthony/NT4.0/tree/master/private/ntos/...