Learn More from Books
Design of 4.4BSD Operating System
McKusick, Bostic, Carels, Quarterman
Firewalls with Linux and OpenBSD
Sonnenreich & Yates
Building Internet Firewalls, 2e
Elizabeth Zwicky, O'Reilly.
Hacking Exposed
McClure, Schambray, Kurtz
UNIX System Administration, 2e
Nemeth et al.
See http://www.openbsd.org/books.html