Explanation:

There are several types of firewall configurations:

Packet filter – Packets cannot pass through the firewall unless they match the established rule set configured in the firewall. Traffic can be filtered based on different attributes, such as source IP address, source port or destination IP address or port.
Stateful packet inspection (SPI) – This is a firewall that keeps track of the state of network connections traveling through the firewall. Packets that are not part of a known connection are dropped.
Application layer – All packets traveling to or from an application are intercepted. All unwanted outside traffic is prevented from reaching protected devices.
Proxy – This is a firewall installed on a proxy server that inspects all traffic and allows or denies packets based on configured rules. A proxy server is a server that is a relay between a client and a destination server on the Internet.