The firewall that Walter has deployed looks at every packet sent by systems that travel through it, ensuring that each packet matches the rules that it operates and filters traffic by. What type of firewall is being described?

This question describes a stateless firewall, which looks at every packet to make decisions about what will be allowed through it. Stateful firewalls pay attention to the conversations and allow packets in a conversation between devices to pass through once it has verified the initial exchange. Next-generation firewalls (NGFWs) build in a wide variety of security services. Application-layer firewalls understand applications that run through them and provide deeper packet analysis capabilities to block unwanted application layer traffic.