How does a proxy server differ from a packet$-$filtering firewall? A proxy server operates at the Application layer, while a packet$-$filtering firewall operates at the Network layer. A proxy server is used to create a screened subnet, while a packet$-$filtering firewall can only be used with screened subnets. A proxy server includes filters for the session ID as well as the IP address and port number. A proxy server can prevent unknown network attacks, while a packet$-$filtering firewall can only prevent known attacks.