The authors should be applauded for never wearing the evangelist's hat. They are forthcoming about the limitations of firewalls. Where firewalls are inadequate, the authors discuss security aspects that must coexist with bastion hosts, proxy servers, and packet-filtering routers. Many believe the onus of protecting networked computers falls on hardware and software. They are wrong.
People protect networks.
The security specialist who writes packet-filtering rules for a router is just as important as the programmer who refrains from attaching an unauthorized modem to her workstation. It's refreshing to see the authors offer advice not only on technical issues, but also on the social aspects of security. The authors are thorough, including information at times that may be obvious to seasoned developers and administrators. This is both a benefit and a drawback. Security is an exacting business, full of minutia.