After testing hundreds of units, the community consensus for the BEST firmware for the 100D is:
| FortiOS Version | Build | Status | Why choose it? | RAM Usage | | :--- | :--- | :--- | :--- | :--- | | 6.0.15 | 6.0.15.0330 | Recommended | Most stable; final patch for 6.0 branch; all security fixes without 6.2’s memory leaks. | ~45% idle | | 6.2.10 | 6.2.10.1923 | Alternative | Last version ever for 100D. Includes features like Security Fabric rating, but can be heavy on RAM (may cause conserve mode). | ~65% idle | | 5.6.13 | 5.6.13.0715 | Legacy Only | Use only if upgrading from 5.4. You must pass through this. | ~30% idle |
Our verdict: If you want "BEST" reliability for a production 100D, download FortiOS 6.0.15.
The 100D has a decent resale value on eBay because of its ASIC chips. Sell it and buy a FortiGate 60F or 80F. The cost of a breach on an EOL device is higher than the cost of a new firewall. Fortigate 100d Firmware Download BEST
You cannot simply upload 6.2.10 over 5.2.0. Here is the mandatory path:
If you are on 5.2.x:
If you are on 5.4.x:
If you are on 5.6.x:
How to upgrade (CLI is safest for EOL devices):
# Copy firmware to TFTP server or SCP
# Reboot and interrupt boot (press any key)
# Type: tftp
# Set the IP and install
Or via GUI: System > Firmware > Upload (Ensure "Upgrade" is selected, not "Install" if preserving config). After testing hundreds of units, the community consensus
You cannot jump directly from an ancient version (e.g., 5.2.9) to the final version (6.2.10) on a FortiGate 100D. The hardware partition layout changes significantly between major versions.
To check your version:
Write this down. You will need the upgrade path. The 100D has a decent resale value on
If you still operate a FortiGate 100D:
Would you like guidance on securely migrating from a 100D to a supported FortiGate model instead?