Showing the netfilter with the OSI layer on the left, after all these years is absolutely clutch and as an educator, I'm thankful the author made such a thing. It's beautiful.

I feel like from an abstraction standpoint, a lot of these concepts get lost when you transition to Windows and in either direction, these pre/post chains never quite made sense to me on the surface. Though, I'm positive it's because I'm not a developer or sysadmin in linux daily. I imagine there's some fascinating stuff you can do.