Which type of gateway can filter packets at the application layer?

Application Level Gateways, commonly referred to as Application Proxies, function at the application layer of the OSI model. These gateways can inspect and filter network traffic based on the data contents of the packets, rather than just their header information. This capability allows them to evaluate the specific requests and responses at a much deeper level, which is essential for securing web-based applications and services.

By analyzing the application data, they can enforce policies regarding allowed communications, block harmful content, or manage traffic more effectively for protocols such as HTTP, FTP, and others. This deep packet inspection is what differentiates Application Level Gateways from other types of gateways, which may only handle communications at lower layers and lack the ability to comprehend or interpret the data being transmitted as per the application layer protocols.

This functionality is crucial in modern network security, where threats can be embedded within legitimate application traffic.