Understanding FTP, FTPS, and SFTP: When to Use Each Protocol

Uploading files to cloud storage is simple, but the underlying protocols—FTP, FTPS, and SFTP—have distinct purposes and security characteristics.

FTP, FTPS and SFTP Overview

FTP

FTP (File Transfer Protocol) is an application‑layer protocol that enables a client to upload files to a server or download files from it. It uses separate command and data channels and is one of the oldest file‑transfer methods.

How FTP Works

When a connection is established, a command channel carries instructions while a data channel transfers the actual file bytes. Because FTP transmits credentials in clear text, it is vulnerable on public networks, prompting the development of secure variants.

FTPS

FTPS adds SSL/TLS encryption to FTP and comes in two modes:

Implicit SSL: runs on port 990; the entire session is encrypted from the start.

Explicit SSL: uses the standard FTP port 21; the client first establishes an unencrypted connection, then issues

AUTH TLS

or

AUTH SSL

to upgrade to an encrypted channel.

SFTP

SFTP (Secure File Transfer Protocol) is built on SSH, not on FTP. It uses a single encrypted connection for both commands and data. Authentication can be performed with a password or an SSH key, providing stronger security.

Active vs Passive Mode in FTP Clients

Active Mode

In active (port) mode, the client opens a random port, sends a

PORT

command to the server, and the server initiates a data connection from its port 20 to the client’s specified port.

Passive Mode

In passive mode, the client connects to the server’s port 21, sends a

PASV

command, and the server opens a random port for data transfer; the client then connects to this server‑opened port.

Active mode is easier to manage on the server side but can be blocked by client firewalls, whereas passive mode is firewall‑friendly for clients but requires the server to listen on additional ports.

Understanding these protocols and modes lets users configure FTP clients more effectively and maintain organized, secure cloud storage.