Data connection mode

When your File Transfer Protocol (FTP) server runs behind a firewall or Network Address Translation (NAT) router, your users may sometimes encounter connectivity issues. One of the most common causes of FTP connection issues is the data connection mode being used. This mode can be either active or passive. Certain firewall configurations will only allow FTP connections if the data connection is set to a mode that works with a given configuration.

This blog will explain the differences between active and passive FTP data connection modes, how they impact firewall configurations and what mode we recommend you use going forward. Although active and passive modes are mentioned in RFC 959, the explanations can be too technical. Before we tackle the main discussion, let’s first review how FTP connections are designed.

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