FTP fails when using fully-qualified domain names (FQDN) in an explicit proxy deployment.
FTP is successful when using the origin content server (OCS)/FTP server's IP address. Connecting directly to the Internet also works when either IP address or FQDN is used.
Note: When this issue occurred, authentication was enabled and the ProxySG appliance username was defined in Raptor login syntax.
Use the appliance's packet capture utility (PCAP) to compare packet captures from when FTP worked with captures from when FTP failed.
You could use the following PCAP filter expressions:
Troubleshoot the issue depending on the information in the packet captures. The following are possible causes of the issue and examples of troubleshooting steps: