I. Describe that an application layer firewall or application firewall, is frequently installed on a dedicated computer, separate from the filtering router, but is commonly used in conjunction with a filtering router.
II. Identify how the application firewall is also known as a proxy server, since it runs special software that acts as a proxy for a service request.
III. Emphasize that since the proxy server is often placed in an unsecured area of the network or in the DMZ, it—rather than the Web server—is exposed to the higher levels of risk from the less trusted networks.
IV. Define the four common applications these firewalls protect at the application layer:
• File Transfer Protocol (FTP)
• Telnet
• Hypertext Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP) or Simple Network Management Protocol (SNMP)