Plesk backup to a remote FTP server fails: Curl error: (28) Timeout was reached

Symptoms

Plesk backup to a remote FTP server fails with one of the following errors:

Error: Transport error: unable to list directory: Curl error: (28) Timeout was reached: Last FTP request: LIST Last FTP response: 200 Type set to A

Transport error: unable to list directory: Curl error: (28) Timeout was reached: Last FTP request: PASV Last FTP response: 229 Entering Extended Passive Mode (|||5985|)

Cause

The FTP ports on the remote FTP server are filtered by a firewall.

Resolution

For remote FTP backups to work, make sure that these ports are open.

• On the FTP server

  • Incoming and outgoing connections:
    20 - FTP data transfer for active mode (TCP)
    21 - FTP (TCP)
  • Incoming connections only:
    49152-65535 - (TCP) for FTP passive mode

• On the Plesk server

  • Incoming and outgoing connections:
    20 - FTP data transfer for active mode (TCP)
    21 - FTP (TCP)