If you're planning on taking the Security+ exam, you should have a basic understanding of how a network perimeter can provide a layer of protection for Internet-facing servers.
For example, can you answer this question?
Q. Your organization hosts a web server and wants to increase its security. You need to separate all web-facing traffic from internal network traffic. Which of the following provides the BEST solution?
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available here.