Description
This is a normal behavior. It does not mean the FTP session is hanging. It is necessary to wait for the file to be downloaded to the FortiGate.
Here are the steps during an ftp download with antivirus enabled:
1) The file is first entirely downloaded to the FortiGate.
2) The file is scanned for viruses on the FortiGate.
3) The file is transferred to the PC (ftp client).
So the PC only 'sees' the FTP packet coming on step 3).
If the ftp server is slow, or the file is big, or the internet connection is slow, it may take some time for the FortiGate to achieve step 1).
To prevent the PC FTP session from timing out, the FortiGate sends 1 byte from time to time to the PC.
