YouTube – Verify and control/limit connections to and use of external systems

Norfolk State University – Administrative Policy: Use of External Information Systems

SANS Whitepaper – Proxies and Packet Filters in Plain English

SANS Whitepaper – Web Application Firewalls

NIST SP 800-77 Guide to IPSec VPNs

NIST SP 800-41 Rev 1: Guidelines on Firewalls and Firewall Policy