What metric is useful for evaluating the effectiveness of a firewall?

The rate of blocked malicious traffic is a key metric for evaluating the effectiveness of a firewall because it directly reflects the firewall's ability to identify and prevent unauthorized access and attack attempts. A high rate of blocked malicious traffic indicates that the firewall is functioning effectively in its primary role of safeguarding the network from threats. This metric helps assess how well the firewall is configured to recognize and react to potential security breaches, thus providing a clear understanding of its protective capabilities.

In contrast, while response time to incidents is important for overall security operations, it primarily measures the efficiency of incident response rather than the proactive defense capabilities of the firewall itself. The number of logs generated can offer insights into the activity on the network, but it does not inherently measure how well the firewall is performing in terms of threat prevention. Similarly, the frequency of updates shows how current the firewall's rules and signatures are but does not provide a direct indication of its effectiveness in blocking attacks. Therefore, focusing on the rate of blocked malicious traffic provides a clear and direct evaluation of the firewall's operational success in protecting the network.