Firmware Download Best | Fortigate 100d
After downloading your "BEST" firmware, you must verify it. Fortinet publishes SHA256 checksums on the download page.
Example for FGT_100D-v6.0.15-build0330-FORTINET.out:
If the hash does not match, DELETE THE FILE. It is corrupted or malicious.
Before we proceed, let’s define what "BEST" means for EOL firmware:
The BEST download is always directly from Fortinet’s official Support Portal—even for EOL devices. Fortigate 100d Firmware Download BEST
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.
If you are on a much older version, you must follow a strict path: After downloading your "BEST" firmware, you must verify it
Current Version → Intermediate → Target (v6.0.15)
| Starting Version | Required Intermediate Step | | :--- | :--- | | v5.2.x or v5.4.x | Upgrade to v5.6.13 first | | v5.6.x | Upgrade to v6.0.15 directly | | v6.0.0 – v6.0.7 | Upgrade to v6.0.15 directly |
Critical: Do not skip major versions. Always backup config before upgrade. Downgrading from v6.0.15 to older v6.0.x requires a factory reset.
Do not attempt to download the latest FortiOS (v7.2, v7.4, or v7.6). The FortiGate 100D reached its End of Life (EOL) and End of Support (EOS) dates. If the hash does not match, DELETE THE FILE
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).