Which firewall intercepts information running through a gateway and accepts only packets that are generated by a specific protocol such as FTP or SMTP?

A Caching Proxy stores copies of frequently accessed content to improve performance, but does not filter packets based on protocol compliance at the gateway level.

Packet Filtering firewalls examine packets based on source/destination IP addresses, ports, and protocols at the network layer, but do not perform deep application-layer protocol inspection.

An Application Proxy (also called an application-layer gateway) intercepts all traffic passing through it and evaluates packets based on specific application-layer protocols such as FTP, SMTP, or HTTP. It acts as a relay, accepting connections from clients and making separate connections to destination servers, ensuring only protocol-compliant traffic is allowed through.

A Circuit-Level Gateway operates at the session layer and validates TCP/UDP sessions, but does not inspect the content or enforce application-specific protocol rules.

Network Address Translation (NAT) translates private IP addresses to public ones and vice versa, providing a degree of obscurity, but is not a firewall mechanism for protocol-based packet acceptance.