Application proxy firewalls act as intermediaries between the client and the server. Rather than allowing the client to communicate directly with the server, the proxy firewall handles the communication on behalf of the client. It intercepts the client's requests, examines them, and then forwards valid requests to the server. This adds a layer of security because the server is not directly exposed to potentially malicious traffic.
Other Incorrect Statements:
"They are easier to configure than packet filtering firewalls": This is not true. Application proxy firewalls are typically more complex to configure because they operate at a higher layer (the application layer) and need to understand the specific protocols and applications in use.
"They are stateless and do not track sessions": This is incorrect. Application proxy firewalls are generally stateful, meaning they track the state of active sessions and can monitor the full context of a session, including application-layer data.
"They operate at the network layer": This is also incorrect. Application proxy firewalls operate primarily at the application layer (Layer 7 of the OSI model), where they inspect and filter traffic at the level of individual applications or protocols (like HTTP, FTP, etc.).
How does a circuit-level firewall differ from an application proxy firewall?