Internet security, cyber security, is aimed at monitoring the application, since attackers use it for their attacks. Thus, with the Application Layer Gateway (ALG) or Web Application Firewall(WAF), there are security concepts that focus on the application and protect the protocols of the application layers, such as e-mail or HTTP.
Application layer gateways control the data content of the protocols and detect protocol violations. They block viruses, worms, Trojans, and other malware by filtering data based on protocol types, file formats, URLs, and active content.
Application Layer Gateway (ALG) are implemented to control firewalls. They provide security for individual applications without special protection against attacks. ALG gateways operate at the application layer and use proxy agents to incorporate contextual information into the decision-making process to increase the level of security. The proxies play an active role in communication between end systems, such as opening communication ports. Each application requires its own proxy.