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.
This article describes that in some cases, automatic upgrade(via GUI) fails because of too many factors like FortiGate is unable to connect to the FortiGuard server or there is a delay in connecting to the server to complete the firmware download and upgrade.
Scope
FortiGate.
Solution
In the event that the message 'Image upgrade failed' appears, see below workarounds to avoid this error on the next upgrade.
1) Use another browser, clear Cache and Cookies, or use an incognito Window to login to FortiGate GUI and then, try to perform the automatic upgrade (online).
2) If the above step did not help, manually download and install the firmware from the support portal: (firmware version for the FortiGate model)
Manually upgrade the FortiaGte by using System -> Firmware- > Upload Firmware -> Browse and use this file.
If both steps do not work, open a TAC case for further troubleshooting, analysis, and resolution.
