Unable to retrieve FTP directory listing via SSL/TLS secured connection

Symptoms

• Unable to connect to the server via FTP, the process times out after 20 seconds:

  227 Entering Passive Mode (203,0,13,2,119,129).
  ftp: connect: Connection timed out

  OR

  Error: Connection timed out after 20 seconds of inactivity Error: Failed to retrieve directory listing

• Connection to FTP from localhost on the server itself works fine:

  Status: Connecting to 203.0.113.2...
  Status: Connection established, waiting for welcome message... 
  Status: Initializing TLS... 
  Status: Verifying certificate... 
  Status: TLS connection established. 
  Status: Connected 
  Status: Retrieving directory listing...

• The nmap utility shows that the passive port range (49152-65535) is in the closed state:

  # nmap -p49192,65535 203.0.13.2
  Host is up (0.25s latency). 
  PORT STATE SERVICE 
  
  49192/tcp closed unknown 
  65535/tcp closed unknown

Cause

Firewall/NAT misconfiguration in between the Plesk server and the end-user.

Resolution

Ensure that passive port range is configured on a Firewall and in Plesk:

For Linux:

• How to configure a passive ports range for ProFTPd on a server behind a firewall?

For Windows:

• How to configure a passive FTP port range in Plesk for Windows?