Compare or discuss the differences between any two security systems.

A comparison of firewalls and Intrusion Detection Systems (IDS) illustrates their distinct roles in network security. Both contribute to defense, but they operate differently.

A firewall functions as a gatekeeper, regulating network traffic based on a predefined rule set. Its objective is to prevent unauthorized network access or block specific traffic types. Firewalls inspect packet headers, such as IP addresses and port numbers. Application-level firewalls can examine application data. They are commonly deployed at network perimeters to separate internal networks from external ones. A firewall's action is proactive; it permits or denies traffic according to its rules.

An Intrusion Detection System (IDS) monitors network traffic or system activities for malicious actions or policy breaches. It then generates alerts or logs these events. Unlike firewalls, an IDS generally does not block traffic; its role is detection and notification. IDSs can be signature-based, identifying known attack patterns, or anomaly-based, recognizing deviations from normal behavior. They are often placed within the network, sometimes behind a firewall. An IDS might detect a port scan or an attempted exploit, but it typically does not prevent the initial connection.

In short, a firewall acts as a preventative control, filtering traffic and creating a barrier. An IDS serves as a detective control, monitoring for suspicious activity and offering insight into potential compromises as they occur or are underway.