Sep 1, 2020

FON-175 POST Mode Recovery (Factory Reset)


If you need to do a factory restore on a Fortinet FON-175 (or FON-175i, FON-375, FON-375i) device, they will send you a document that refers to the "Post Mode" in order to do a recovery via post mode. While the document is helpful, I couldn't make the recovery work as it was written.

In the document, it suggests you use FileZilla FTP Server. For whatever reason, I could not get the phone's built-in ftp client to connect to FileZilla. After much hair-pulling and Googling, I stumbled across another ftp server to use instead of filezilla: CoreFTP Server.

The setup is a little wonky, but in a nutshell:

  • Click the SETUP button at the top.
  • Click NEW in the "Domains" section
  • Type the IP you chose for your IPv4 (192.168.10.x)
  • Set the Base Directory to the folder where you stored your firmware
  • Click OK
  • Select your new domain
  • Click NEW in the "User" section
  • Enter a username
  • Enter a password
  • Set the HOME DIRECTORY to the location of the firmware file
  • Check the "Always Allow Login" option
  • Click OK
  • Click OK to exit SETUP
  • Click the "View Activity" option

Once you have done that, follow the steps outlined in the Post Mode document.

By the way, there is a version of the document online here (though in a foreign language):

*Note: even though this method allowed me to update my phone, the phone itself was still bricked. It kept rebooting after getting to the user screen. At least it was worth a shot.


  1. Confirming as of 4/20/2023 8pm and 3 hours later. This method works!!!! Thank you! Remember to turn off all local firewall configurations, so the Phone can access the local machine. Regards, EF and JR

  2. Also, something that was listed here. After giving up all hope, before disabling the local FW. We did run option "a" which doesn't show in the option but it showed in mine. It says Format File System. Might want to try that out also. Before updating. Order was 3, a, 2.

  3. Last, the translation. Foreign language was indonesian.

    Here's a tutorial for troubleshooting IP Phone Fanvil with Post Mode error messages.

    Connect PC to IP Phone LAN port directly (direct).
    Set the IP Address on the PC with segment 192.168.10.X/24
    Open CMD (Command Promt) then telnet to IP Address (default IP Phone IP Address). The following is the display after telnet login:

    Clear configuration by selecting menu number 3 then pressing enter. Here's how it looks:

    Enter the firmware on the FTP server (eg FileZilla server), because the next step is to update the firmware via FTP. After the firmware is on the FTP server, run menu number 2 FTP Update Image by typing number 2 then press enter. Then enter the FTP server address, image name (firmware name),
    FTP username and FTP password. Here's how it looks if the firmware update process is successful
    After a successful firmware update select menu number 4 Exit and Reboot.