Navigate to Download > Firmware Images . Select FortiGate as the product and browse the folder structure to find the 100D specific builds.
Use the Fortinet Upgrade Path Tool to see the mandatory "hops" or intermediate versions you must install first. 3. Installation Steps Fortigate 100d Firmware Download BEST
Before updating your FortiGate 100D firmware, consider the following best practices: Navigate to Download > Firmware Images
Write this down. You will need the upgrade path. "Memory leak after 2 weeks of uptime
"Memory leak after 2 weeks of uptime." Fix: The v5.4.x branch has a known memory leak with WAD (Web Application Delivery) processes. The best fix is a weekly reboot. Set a scheduled script: config system auto-script edit "weekly-reboot" set interval 604800 set script "execute reboot" next end
Because the 100D is EOL, it will not receive updates for new CVEs (Common Vulnerabilities and Exposures). You must harden your configuration.
For the 100D, the 6.2 branch (specifically versions like 6.2.13 or later) is often considered the terminal stable point. It balances modern security features with the hardware's CPU and RAM limits.