At which layer of the OSI model do the most popular types of proxy-oriented firewalls operate?

Proxy-oriented firewalls primarily operate at the application layer of the OSI model. This layer is responsible for the interaction between the user and the application, enabling protocols that support specific network services such as HTTP, FTP, and SMTP.

These firewalls act as intermediaries between clients and servers. By examining traffic at the application layer, they can filter requests based on certain attributes, such as URL or content type, and make decisions on whether to allow or deny traffic. This level of control is particularly effective for preventing unwanted access and for monitoring potentially harmful payloads that could exploit application vulnerabilities.

Since proxy-oriented firewalls function at a high level of the OSI model, they have the ability to inspect and manipulate the data being transmitted, unlike lower-layer firewalls, which generally handle traffic based on IP addresses and ports without understanding the content.