To answer this question, let's go through each option to understand why it is correct or incorrect:
Option A) A screening router - This option is correct. A screening router is a device that filters network traffic based on predefined rules. It can be used as part of a network's perimeter defense to block or allow specific traffic based on the configured rules.
Option B) A firewall - This option is correct. A firewall is a device or software that monitors and controls incoming and outgoing network traffic. It acts as a barrier between a trusted internal network and untrusted external networks, protecting the internal network from unauthorized access or malicious activity.
Option C) A proxy server - This option is incorrect. A proxy server can be used as part of a network's perimeter defense. It acts as an intermediary between clients and servers, forwarding requests from clients to servers and returning responses from servers to clients. It can provide additional security by filtering and inspecting network traffic, blocking access to certain websites or services, and caching frequently accessed content.
Option D) None of the above - This option is incorrect. Both a screening router and a firewall can be part of a network's perimeter defense, while a proxy server can also be used for security purposes.
The correct answer is C) A proxy server. This option is incorrect because a proxy server can be part of a network's perimeter defense.