4-1-5 FTP (File Transfer Protocol) Explained

Key Concepts

• FTP Basics
• FTP Modes
• FTP Commands
• FTP Security

FTP Basics

FTP (File Transfer Protocol) is a standard network protocol used for transferring files between a client and a server on a computer network. FTP operates on the client-server model, where the client initiates a connection to the server to upload or download files. FTP supports both text and binary file transfers, making it versatile for various types of data.

FTP Modes

FTP operates in two primary modes:

• Active Mode: In active mode, the client opens a port and listens for a connection from the server. The server then initiates a connection to the client's specified port to transfer data.
• Passive Mode: In passive mode, the server opens a port and listens for a connection from the client. The client then initiates a connection to the server's specified port to transfer data. Passive mode is often used to overcome firewall issues that can arise in active mode.

FTP Commands

FTP uses a set of commands to manage file transfers and directory operations. Some common FTP commands include:

• USER: Sends the username to the server for authentication.
• PASS: Sends the password to the server for authentication.
• LIST: Lists the files and directories in the current directory.
• RETR: Retrieves (downloads) a file from the server.
• STOR: Stores (uploads) a file to the server.
• CWD: Changes the current working directory on the server.

FTP Security

FTP was not designed with security in mind, making it vulnerable to various attacks. To enhance security, several secure alternatives have been developed:

• SFTP (SSH File Transfer Protocol): Uses SSH to encrypt the data transfer, providing both confidentiality and integrity.
• FTPS (FTP Secure): Extends FTP with SSL/TLS encryption, securing the control and data channels.

Examples and Analogies

Think of FTP as a courier service that specializes in moving packages (files) between different locations. The client (sender) and server (receiver) communicate using a set of instructions (commands) to ensure the packages are delivered correctly. The courier service can operate in different modes, such as the sender waiting for the receiver to pick up the package (active mode) or the receiver waiting for the sender to deliver the package (passive mode).

To enhance security, the courier service can use secure methods like locking the package in a tamper-proof box (SFTP) or using a secure delivery route (FTPS) to ensure the package is not intercepted or altered during transit.