How to troubleshoot FTP connection issues in NAT servers

Introduction

One of the most common causes of FTP connection problems in servers using NAT (Network Address Translation) is having the passive port range blocked by a firewall.

Procedure

By default, the passive port range is 49152-65534. However, this range can be changed. It is best to check your FTP configuration file to confirm the passive port range on your server.

The solution to this problem is to ensure that the passive FTP port range is opened in your server's firewall:

cPanel Docs: How to Enable FTP Passive Mode / Configure the firewall