If you're planning on taking the Security+ exam, you should have a good understanding of firewalls that protect web servers. For example, can you answer this question?
Q. Which of the following operates on the HIGHEST layer of the OSI model, and is the most effective at blocking application attacks?
D. Stateless firewall
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available here.