An interesting fact is that packet filtering as a problem domain has been dominated by in-kernel virtual machines going back into the 1980s; it's an idea that comes all the way from Xerox.
Need to know what's type of water the people at Xerox Palo Alto were drinking.
They pioneered many groundbreaking and game changing works on computing including (but not limited to) windowing desktop environment, integrated programming/structural editor with CEDAR/Tioga, SQL (team moved to Oracle), Ethernet networks, laser printer, VLSI and Jupiter operational transform for distributed computing (precursor to CRDT). Each of this technology is now an industry of its own.
