digicert – Mitigating Risk: The Importance of Considering Your Certificate Practices

SANS Whitepaper – Building and Managing a PKI Solution

Colorado Department of Education – Network Firewall Implementation Policy

Texas Wesleyan University – Sample Firewall Policy

Microsoft – Firewalls

SANS Whitepaper – Achieving Defense-in-Depth with Internal Firewalls

Microsoft – Perimeter Firewall Design

NIST SP 800-171A Assessing Security Requirements for Controlled Unclassified Information

SANS Whitepaper – Proxies and Packet Filters in Plain English

Avast – What is a Proxy Server?