Learn about FTP/FTPS/SFTP file transfer protocols in one article

Introduction to FTP

FTP (File Transfer Protocol) is a protocol for file transfer over a computer network. It allows users to transfer files from one computer to another over a network. FTP uses a client-server model, where the client connects to the server through FTP client software and authenticates using a username and password.

FTP supports a variety of operations, including uploading files to the server, downloading files from the server, deleting files on the server, renaming files, etc. Users can perform these operations through FTP client software or through the command line interface using FTP commands.

Example command to upload a file using FTP:

1. Connect to FTP server:

 ftp <服务器地址>

2. Enter your username and password to log in:

 <用户名> <密码>

For example:

 myusername mypassword

3. Change to the directory where you want to upload the file:

 cd <目录路径>

For example:

 cd /path/to/upload/directory

4. Set the transfer mode to binary mode:

 binary

5. Start uploading files:

 put <本地文件路径>

For example:

 put /path/to/local/file.txt

6. After the upload is complete, disconnect from the FTP server:

 bye

How FTP works

The FTP protocol is based on a client-server model, in which the client establishes a connection with the server through the FTP client software and sends and receives files through the connection.

1. Establish a connection: The client uses the FTP client software to establish a connection with the server. Usually the default port number 21 of the TCP protocol is used for connection.
2. Authentication: After the client establishes a connection, it needs to provide a username and password for authentication. These credentials are used to verify whether the client has permission to access files on the server.
3. Directory Navigation: Once authentication is successful, the client can use FTP commands to navigate the directory structure on the server. Common commands include CD (change directory), LS (list directory contents), etc.
4. File transfer: The client can use FTP commands to upload and download files. When uploading files, the client sends local files to the server; when downloading files, the client obtains files from the server.
5. Data transmission mode: FTP supports two data transmission modes: active mode and passive mode. In active mode, the server actively connects to the client's data port for data transmission; in passive mode, the client actively connects to the server's data port for data transmission.
6. Disconnect: When the file transfer is complete or the connection is no longer needed, the client can disconnect from the server by sending the QUIT command.

The working principle of FTP is to realize the function of file transfer on a computer network through steps such as establishing connection, identity authentication, directory navigation and file transfer.

Differences between FTP data transmission modes

In FTP, there are two different data transmission modes: Active Mode and Passive Mode.

1. Active Mode: In active mode, the client first establishes a control connection to the server's FTP control port (default is 21). When data needs to be transferred, the client randomly selects a port (called N) and notifies the server, and then the server tells the client to use a new data connection to transfer data through the control connection. In active mode, the data connection is initiated by the server, and the client acts as the data receiver.
2. Passive Mode: In passive mode, the client first establishes a control connection to the FTP control port of the server. When data needs to be transferred, the server randomly selects a port (called N) and notifies the client, and then the client tells the server to use a new data connection to transfer data through the control connection. In passive mode, the data connection is actively initiated by the client, and the server acts as the data receiver.

The difference between active mode and passive mode lies in the way the data connection is established. In active mode, the server actively initiates the data connection, while in passive mode, the client actively initiates the data connection. The choice of these two modes depends on the network environment and the configuration of the firewall. In some cases, the active mode may be restricted by the firewall, while the passive mode can better adapt to various network environments. Therefore, when using FTP for data transmission, it is necessary to choose the appropriate mode according to the specific situation.

Introduction to FTPS

FTPS (File Transfer Protocol Secure) is a secure file transfer protocol that adds an SSL/TLS encryption layer to FTP (File Transfer Protocol) to protect the security of data transmission.

FTPS enables encrypted file transfer between the client and the server. It uses the SSL/TLS protocol to encrypt and authenticate data, ensuring data security and integrity during transmission.

FTPS can be transmitted in two modes: explicit mode and implicit mode. In explicit mode, the communication between the client and the server is always in plain text, but SSL/TLS is used for encryption when establishing a data connection. In implicit mode, the entire communication process is encrypted.

FTPS can effectively protect sensitive data during file transfer and prevent data from being stolen or tampered with. It is widely used in scenarios where data security needs to be protected, such as website file upload, backup, and remote file management.

Introduction to SFTP

SFTP (Secure File Transfer Protocol) is a secure file transfer protocol used to securely transfer files over a computer network. It uses SSH (Secure Shell) protocol for encryption and authentication to ensure confidentiality and integrity of file transfers.

SFTP can be used to achieve the following functions:

• File upload and download: You can upload files from your local computer to a remote server, or download files from a remote server to your local computer.
• File and directory management: Files and directories can be created, deleted, renamed, and moved.
• Permission control: You can set permissions for files and directories to limit users' access to and operations on files.
• Resume transfer: If the file transfer process is interrupted, SFTP can resume the transfer and continue from where it was interrupted.

To use SFTP for file transfer, you need an SFTP client software (such as FileZilla, WinSCP, etc.) and an SFTP server. When connecting to the SFTP server, you need to provide the server address, port number, user name and password (or use SSH keys for authentication).

Example command to upload a file using SFTP:

 sftp username@hostname put local_file remote_file

Among them, username is the username of the remote server, hostname is the address of the remote server, local_file is the file path on the local computer, and remote_file is the path where the file is saved on the remote server.

Common FTP Tools

1. FileZilla: FileZilla is a free, open source FTP client that supports Windows, Mac, and Linux operating systems. It has an intuitive user interface that makes it easy to manage and transfer files.
2. WinSCP: WinSCP is a free and open source SFTP, SCP and FTP client for Windows. It provides a graphical interface and command line interface, and supports file transfer, file management and remote command execution.
3. CuteFTP: CuteFTP is a powerful commercial FTP client that supports Windows operating system. It has an intuitive user interface and rich functions such as file transfer, folder synchronization, file editing, etc.
4. Cyberduck: Cyberduck is a free FTP and cloud storage client that supports Windows and Mac operating systems. It supports multiple protocols, including FTP, SFTP, WebDAV, Amazon S3, etc., which can easily manage and transfer files.

These tools provide easy-to-use interfaces and rich functions to meet the needs of most FTP operations.