When a firewall functions as anApplication-Level Gateway (ALG), it intercepts, inspects, and dynamically manages traffic at theapplication layerof the OSI model. The primary role of an ALG is to providedeep packet inspection (DPI), address translation, and protocol complianceenforcement.
To establish a connection successfully, an ALG requires apinhole—a temporary, dynamically created rule that allows the firewall to permit the return traffic necessary for specific applications (e.g., VoIP, FTP, and SIP-based traffic). Thesepinholesare essential because many applications dynamically negotiate port numbers, makingstatic firewall rules ineffective.
For example, when aSession Initiation Protocol (SIP)application initiates a connection, the firewalldynamically opens a pinholeto allow the SIP media stream (RTP) to pass through while maintaining security controls. Once the session ends, the pinhole is closed to prevent unauthorized access.
Firewall Deployment– ALGs are commonly deployed in enterprise network firewalls to manage application-specific connections securely.
Security Policies– Firewalls use ALG security policies to allow or block dynamically negotiated connections.
VPN Configurations– Some VPNs rely on ALGs for handling complex applications requiring NAT traversal.
Threat Prevention– ALGs help detect and prevent application-layer threats by inspecting traffic content.
WildFire– Not directly related, but deep inspection features like WildFire can work alongside ALG to inspect payloads for malware.
Panorama– Used for centralized policy management, including ALG-based policies.
Zero Trust Architectures– ALG enhances Zero Trust by ensuringonly explicitly allowed application trafficis permitted through temporary pinholes.
References to Firewall Deployment and Security Features:Thus, the correct answer isA. Pinholebecause it enables a firewall to establish application-layer connections securely while enforcing dynamic traffic filtering.
