According to the FortiOS 7.6 Study Guide and technical documentation, conserve mode is a protective state triggered when memory utilization reaches the Extreme Threshold (typically 95% by default). When this occurs, the FortiGate implements several measures to prioritize system stability over new functionality. One of the primary restrictions is that the FortiGate refuses to accept configuration changes (Statement B). This prevents the system from initiating new processes or allocating additional memory that could lead to a total system crash.

Regarding traffic handling, the behavior is determined by specific " fail-open " settings. For the IPS engine, if the fail-open global setting is enabled, the FortiGate continues to transmit packets without IPS inspection (Statement D). This ensures that network connectivity is maintained even when the system lacks the memory resources to perform deep packet inspection. In contrast, Statement A is incorrect because the system may skip non-essential actions to save memory. Statement C is incorrect because conserve mode is designed to avoid a system halt; the device remains operational and will automatically exit conserve mode once memory usage drops below the Release Threshold (typically 82%).