C: Proxies can prevent potential threats from reaching your network without blocking the entire connection.
D: A proxy operates at the application layer, as well as the network and transport layers of a TCP/IP packet, while a packet filter operates onlyat the network and transport protocol layers.
Incorrect:
Not A: A packet filter examines each packet's IP header to control the network traffic into and out of your network.
Reference: Fireware Basics, Courseware: WatchGuard System Manager 10, page 95