In network security, what is the primary purpose of a firewall?

The primary purpose of a firewall is to control the flow of network traffic. Firewalls are designed to establish a barrier between a trusted internal network and untrusted external networks, such as the internet. By doing so, they monitor and filter incoming and outgoing traffic based on predetermined security rules. This functionality is critical for protecting sensitive data and preventing unauthorized access to network resources.

Firewalls play a proactive role in network security management, allowing administrators to define what traffic is permissible and what should be blocked, effectively managing potential threats. This helps to maintain the integrity and confidentiality of the network, reducing the risk of attacks and data breaches.

In the context of the other options, enhancing internet speed is not the primary function of a firewall; rather, firewalls can sometimes introduce latency due to their filtering processes. Encrypting sensitive information is a task typically handled by other security measures like VPNs or encryption protocols, and preventing hardware failure is unrelated to the roles of firewalls in network security. Thus, the focus on controlling traffic flow accurately captures the essence of a firewall's purpose in security architecture.