Which network configuration is needed in the firewall at the exit to the internet?

A Layer 3 configuration is appropriate for firewalls at the exit to the internet because it operates at the network layer of the OSI model, where it can manage IP addresses for routing both ingress and egress traffic. This capability allows the firewall to make forwarding decisions based on the IP addresses of packets, ensuring that the correct packets are sent to their intended destinations and can enforce security policies related to that traffic.

By configuring the firewall at Layer 3, you can also implement advanced routing features and manage network address translation (NAT), which is often necessary for translating private IP addresses to public ones as traffic exits the network. This configuration provides robust security and traffic control for communication between a private network and the wider internet, effectively allowing the firewall to inspect and filter traffic based on established rules.

Other configurations, such as Layer 2, might not adequately handle IP routing needs required at the internet boundary, while configurations like Layer 4 focus on transport-level protocols and do not provide the necessary routing capabilities associated with internet communication. Virtual wire, on the other hand, is used for transparent firewall deployments but lacks the necessary functionalities for handling IP address routing for this scenario.