Before every single step in the upgrade path, download a full configuration backup.
While new features are gone, Fortinet occasionally releases critical security patches for older OS versions if a major vulnerability is discovered. Where to Download FortiGate 100D Firmware Fortigate 100d Firmware Download BEST
Older hardware like the 100D can struggle with "Conserve Mode" on newer firmware. If you experience high memory usage, you may need to stay on a mature 6.0.x build. The Recommended Upgrade Path Before every single step in the upgrade path,
Always have a console cable connected during the upgrade so you can monitor the boot process and catch any errors in real-time. If you experience high memory usage, you may
Navigate to Download > Firmware Images . Select FortiGate as the product and browse the folder structure to find the 100D specific builds.
Use the MD5 or SHA256 checksums provided on the Fortinet support site to verify the integrity of your downloaded file.