Hi, i was just asked today, but i couldn't answer precisely so that's why i'm asking here :-)

There is any book about Firewall design and implementations (Unix environment and C)?

For sure, i could recommend TCP/IP books, and what i did, but there is some design decisions, that are not related with TCP/IP. For sure, i said about the netfilter/iptables (RTFSC) but as well we cannot assume that the netfilter/iptables is the best approach since we don't have too many baselines (ok, we could compare it with PF, but again, read source code to understand design decisions is not always the best way).

So if anybody knows a book about this theme, please shoot it!