Рекомендую всем книжку "Building Firewalls with OpenBSD and PF"
About This Book
Title: Building Firewalls with OpenBSD and PF, 1st ed.
Author: Jacek Artymiak
pages: 247
The first and only print publication devoted solely to the subject of the pf packet filter used in DragonFly BSD, OpenBSD, FreeBSD, and NetBSD operating systems.
Written by Jacek Artymiak, a frequent contributor to ONLamp.com, Building Firewalls with OpenBSD and PF is the first and only print publication devoted solely to the subject of the pf packet filter used in DragonFly BSD, OpenBSD, FreeBSD, and NetBSD operating systems. Topics covered include: firewall design, ruleset syntax, packet normalization (scrubbing), packet redirection (masquerading), packet filtering, bandwidth management (ALTQ), load balancing, and more.
"Yea, just checked out 'The Design and Implementation of the FreeBSD Operating System' by Marshall Kirk McKusick. While not specifically OpenBSD, it's solid knowledge that can be applied to other BSDs. Worth a read if you're looking for deeper dive into the underlying tech."