LogID 0100032002: Conserve Mode Flapping & Threshold Hysteresis
Continuous cycling between LogID 0100032001 (system entered conserve mode) and LogID 0100032002 (system exited conserve mode) causes acute session thrashing, application timeouts, and HA heartbeat jitter on FortiGate branch and campus firewalls when memory hovers within the default 6% hysteresis band.
Technical Root Cause Analysis
FortiOS enforces a state hysteresis mechanism to govern entry and exit from memory conserve mode. The kernel's conserve manager enters conserve mode at 88% memory utilization (Red Threshold) and clears conserve mode only after physical memory recedes below 82% (Green Threshold).
When baseline memory sits near 84–86%—frequently observed on 2GB and 4GB models running extensive ISDB tables, DNS filtering, and SSL inspection—small bursts in HTTP proxy connections push utilization above 88%. This immediately invokes conserve mode, prompting user-space daemons to purge local request caches. As caches drop, memory dips to 81.9%, triggering LogID 0100032002 (exit). With conserve mode lifted, traffic resumes full inspection, immediately pushing memory back to 88.2% (LogID 0100032001). This flapping cycle can repeat dozens of times per hour, severely degrading user application connections.
Platform Vulnerability & Hysteresis Margin Matrix
| Platform Family | Physical RAM | Default Flapping Risk | Recommended Hysteresis Gap |
|---|---|---|---|
| FortiGate 40F / 60F | 2 GB | High (Narrow Headroom) | Green: 75% | Red: 88% (13% gap) |
| FortiGate 70F / 80F | 4 GB | Moderate-High | Green: 78% | Red: 88% (10% gap) |
| FortiGate 100F / 200F | 4 GB – 8 GB | Low (Unless Heavy Proxy) | Green: 80% | Red: 88% (8% gap) |
Platform Impact: Predominantly affects branch firewalls (FG-40F through FG-100F) operating near capacity under concurrent web traffic surges and frequent FortiGuard database updates.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to determine the frequency of conserve mode flapping events and inspect current threshold limits:
Diagnostic Commands
# 1. Inspect system crashlog for conserve mode enter/exit flapping timestamps
diagnose debug crashlog read | grep -E "0100032001|0100032002"
# 2. View current global memory threshold parameters
config system global
get | grep threshold
end
# 3. Check live memory utilization, buffer caches, and free RAM
diagnose hardware sysinfo memory
# 4. Monitor top processes with dynamic 2-second sampling interval
diagnose sys top 2 10Remediation & Workaround Steps (Teaser Preview)
Follow the complete step-by-step remediation guide in the Ferrite interactive platform:
Frequently Asked Questions
By default, FortiOS enters conserve mode at 88% RAM and exits when memory falls to 82%. If steady-state memory utilization sits around 84–86%, slight bursts in client web connections or log queuing cause the system to cross the 88% boundary, purge caches, drop below 82%, exit conserve mode, and immediately fill back up—repeating the cycle dozens of times per hour.
Rapid transitions trigger continuous state updates in the HA daemon. If memory-based failover or session sync throttling is enabled, flapping induces severe TCP session resets, SSL re-handshake storms, and potential HA split-brain states.
Administrators should widen the hysteresis band by lowering the green exit threshold (e.g. setting red to 88% and green to 75%) or migrating memory-intensive proxy policies to flow mode, providing ample headroom for routine traffic variance.