I cannot recommend this specific diagram highly enough: https://upload.wikimedia.org/wikipedia/commons/3/37/Netfilter-packet-flow.svg https://upload.wikimedia.o

I cannot recommend this specific diagram highly enough: https://upload.wikimedia.org/wikipedia/commons/3/37/Netfilter-packet-flow.svg https://upload.wikimedia.org/wikipedia/commons/3/37/Netfilte... I've easily had a dozen times where I was able to resolve a complex problem or figure out how to do the thing I wanted to do through examination of this flowchart.