What does a firewall do?

A firewall serves the critical function of blocking unauthorized access to a network while allowing legitimate outbound traffic. This means it acts as a security barrier between a trusted internal network and untrusted external networks such as the internet. By monitoring and controlling incoming and outgoing network traffic based on predefined security rules, the firewall prevents unauthorized access to sensitive data and resources within the network.

For instance, when a device on the internal network tries to connect to the internet, the firewall assesses the request based on its rules to determine if the request should be allowed or blocked. This functionality is essential for maintaining the integrity and security of networked systems, ensuring that only authorized users and applications can communicate with the network.

In contrast, the other options describe functions that are not the primary role of a firewall. Firewalls do not optimize system memory usage, accelerate connections, or specifically protect against malware infection, though they can play a supportive role in an overall security strategy that includes antivirus and intrusion detection systems.