Issues with Image File Transfers Over FortiGate VPN: Compression or Quality Loss?

[Robertdan99]

Hello Fortinet Community,

I’m facing an issue with transferring large photo files over a FortiGate VPN connection, and I’m hoping someone can help me troubleshoot.

I’m a photographer and regularly transfer large, high-resolution image files (RAW and JPEG) from my home office to my team’s server through a FortiGate VPN. Lately, I’ve noticed that some of the files, especially RAW images, seem to lose quality after the transfer, or sometimes the images appear slightly corrupted or compressed.

Here’s my setup:
- FortiGate Model: FG-60E
- Firmware: FortiOS v7.0.4
- Connection: FortiClient VPN (IPsec)
- File Sizes: RAW files around 25MB - 50MB each

The original files are perfectly fine before transfer, but once they’re on the server, some seem slightly pixelated or show signs of compression. I’m not sure if it’s a VPN issue, a bandwidth problem, or something with the file transfer protocols. I use FTP for the file transfers. Could this be a data integrity issue with the VPN encryption?

I’ve tried:
- Running the transfer outside of peak hours.
- Using different FTP clients.
- Checking server storage space and bandwidth.

I’ve also thought about using secure file transfer protocols (like SFTP) instead of plain FTP, but I’m unsure if that will make a difference in this case.

Has anyone else experienced similar issues when transferring large files or images. over a FortiGate VPN? Any suggestions on troubleshooting or alternative solutions would be greatly appreciated.

Thanks in advance!

[Raghu_Kumar]

Hi,

It sounds like you might be dealing with packet fragmentation or integrity issues during transfer. I recommend switching to SFTP or FTPS instead of plain FTP, which provides better encryption and integrity checks. Also, try adjusting the MTU/MSS settings on your VPN to avoid fragmentation (set MSS to 1350). Monitoring packet loss and bandwidth during the transfer could help too. Lastly, ensure your FTP client has file integrity checks enabled (MD5 or SHA-1).

https://community.fortinet.com/t5/FortiGate/Technical-Tip-MTU-override-of-IPsec-VPN-interface/ta-p/1...