Which type of firewall operates at the application layer of the OSI model and inspects incoming and outgoing data packets?

A proxy firewall, also known as an application-level firewall, operates at the application layer of the OSI model. It examines incoming and outgoing data packets to filter requests and responses based on specific application-level protocols, such as HTTP, FTP, or DNS. This type of firewall acts as an intermediary between the client and the server, making it highly effective for controlling access to web applications and protecting against certain types of attacks, like cross-site scripting. Option A (Packet-filtering firewall) is incorrect because packet-filtering firewalls operate at the network or transport layers and do not inspect the content at the application layer. Option C (Stateful inspection firewall) is incorrect because stateful firewalls track the state of active connections but do not provide as deep an inspection as proxy firewalls at the application level. Option D (Network firewall) is a general term and does not specify the application-level functionality that a proxy firewall offers. Option E (Static firewall) is incorrect because static firewalls typically refer to simple, statically-configured rules, which do not involve dynamic inspection of application-layer traffic.