FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 198502



This article describes the changes to conserve mode self protection mechanisms in 5.6.




FortiGate 5.6.




The main differences are as follows:

  • No more distinction between 'kernel' versus 'Proxy' or 'system' types of conserve mode.
  • Definitions for 3 thresholds: 'green', 'red', 'extreme', all adjustable through the CLI.
  • A new trigger based on 'memory used'.
  • New event logs.
  • New diagnose command 'diagnose hardware sysinfo conserve'.
  • New conserve mode stats in proxy stats via 'diag sys proxy stats all' (see the conserve_mode line).

3 memory thresholds: green, red, and extreme.


'red' and 'extreme': Both 'red' and 'extreme' are thresholds to enter in 'conserve mode' when the system memory used is over their thresholds.

When the used memory goes over the defined red threshold, the kernel raises the conserve mode state. FortiGate functions reacting to conserve mode state, like antivirus transparent proxies, would apply their own restriction based on their settings.
If the used memory continues to increase and reach the 'extreme' threshold, conserve mode actions taken with the red threshold are still active and additionally new sessions will be dropped.
'green': When used memory goes below the 'green' threshold, kernel releases the conserve mode state. FortiGate functions reacting to conserve mode state would stop their restriction measures.

Configurable thresholds.


Though it is recommended to keep the default memory threshold, a new CLI command has been added to allow administrators to adjust the thresholds.

Default values are : 
  • Red: 88% of total memory  is considered "used memory"
  • Extreme: 95% of total memory is considered "used memory"
  • Green: 82% of total memory is considered 'used memory'.


Configuration (CLI only):


config system global
set memory-use-threshold-extreme 95
set memory-use-threshold-red 88
set memory-use-threshold-green 82

Diag command:


diagnose hardware sysinfo conserve
memory conserve mode: off
total RAM:                            994 MB
memory used:                          448 MB   45% of total RAM
memory used threshold extreme:        944 MB   95% of total RAM
memory used threshold red:            874 MB   88% of total RAM
memory used threshold green:          815 MB   82% of total RAM