Fraser, B. "Site Security Handbook RFC 2196." http://www.ietf.org/rfc/rfc2196.txt; September 1997.
Malik, S. Network Security Principles and Practices. Indianapolis, Indiana: Cisco Press; 2003.
Pfleeger, C. Security in Computing, 2d ed. Englewood Cliffs, New Jersey: Prentice Hall; 1996.