The FTP (File Transfer Protocol) is a standard network protocol used for transferring files between a client and a server on a computer network. It is one of the oldest and most widely used protocols for file transfer on the Internet.

Here's an overview of how FTP works:

1. Client-Server Architecture: FTP operates on a client-server architecture, where one device (the client) requests files from another device (the server) and the server provides the requested files.

2. Two Modes of Operation:

   • Active Mode: In active mode, the client establishes a control connection to the server on port 21. When the client requests a file transfer, the server initiates a data connection to the client on a separate port (typically port 20) for transferring the actual file data.
   • Passive Mode: In passive mode, the client establishes a control connection to the server on port 21 as usual. However, when the client requests a file transfer, the server opens a random high-numbered port and informs the client, which then establishes a data connection to the server on the specified port to receive the file data.

3. Authentication: FTP supports various methods of authentication for verifying the identity of users, including username/password authentication, anonymous login (where users provide an email address as the password), and anonymous FTP access (where users are allowed to access specific directories without authentication).

4. Commands and Responses: FTP uses a set of commands and responses to control file transfers and interact with the server. Common FTP commands include:

   • USER: Specify the username for authentication.
   • PASS: Specify the password for authentication.
   • LIST: List the contents of a directory on the server.
   • GET: Download a file from the server to the client.
   • PUT: Upload a file from the client to the server.
   • QUIT: Close the connection to the server.

5. Data Transfer: FTP supports two modes of data transfer: ASCII mode and Binary mode. ASCII mode is used for transferring text files, while Binary mode is used for transferring binary files (e.g., images, executables) without any character conversion.

6. Security: Traditional FTP does not encrypt data during transmission, making it vulnerable to eavesdropping and data interception. However, secure variants of FTP, such as FTPS (FTP Secure) and SFTP (SSH File Transfer Protocol), use encryption and secure authentication mechanisms to protect data during transmission.

Overall, FTP is a widely used protocol for transferring files over a network, providing a simple and reliable method for file exchange between clients and servers. Despite its age, FTP remains relevant in many use cases, although newer protocols with enhanced security features are increasingly being adopted for secure file transfer.