Firewalls and Internet Security
Bill Cheswick and Steve Bellovin's 1994 book, the first to teach a broad audience how to build a firewall.
The subtitle, Repelling the Wily Hacker, sets the tone. The authors ran AT&T Bell Labs' internet gateway and wrote down what they had actually learned: filter packets, run as few services as possible on the border machine, and assume that anything reachable from outside will be poked. It arrived just as companies were connecting en masse and helped make the firewall standard equipment.
The most quoted chapter tells of "Berferd", an intruder Cheswick kept in an isolated environment in 1991 so he could watch him for months — an early honeypot. A second edition followed in 2003 with Avi Rubin as third author.