Books

Absolute OpenBSD ISBN-10: 1593274769 ISBN-13: 978-1-59327-476-4
Book of PF ISBN-10: 1-59327-589-7 ISBN-13: 978-1-59327-589-1
Httpd and Relayd Mastery ISBN-10: 1-54675-206-4 ISBN-13: 978-1-54675-206-6
SSH Mastery ISBN-10: 1642350028 ISBN-13: 978-1642350029

 Secure Architectures with OpenBSD
    by Brandon Palmer, Jose Nazario. 
    ISBN 03-21193-66-0 
    April 2004, 520 pp.

 The Design and Implementation of the 4.4BSD Operating System
    by Marshal Kirk McKusick, Keith Bostic, Michael J. Karels, John S. Quarterman 
    ISBN-10: 0132317923 
    ISBN-13: 978-0132317924

Advanced Programming in the Unix Environment (3rd Edition)

    by W. Richard Stevens, Stephen A. Rago

The C Programming Language

    by Brian W. Kernighan and Dennis M. Ritchie

DNSSEC Mastery

    by Michael W. Lucas 
    ISBN-13: 978-1484924471 
    ISBN-10: 1484924479 
    May 2013, 130 pp. 
    Securing the Domain Name System with BIND

TCP/IP Illustrated, Volume 1

    by W. Richard Stevens

IPsec: The New Security Standard for the Internet, Intranets and Virtual Private Networks

    by Naganand Doraswamy and Dan Harkins

Computer Networks

    by Andy Tanenbaum

DNS and BIND

    by Paul Albitz and Cricket Liu

DHCP

    by Ted Lemon and Ralph E. Droms