File Transfer Protocol (FTP)
1. Introduction
FTP is a standard network protocol used to transfer files between a client
and a server over a TCP/IP network (such as the Internet).
It operates on the application layer of the OSI model.
FTP follows a client-server model, where:
Client: Requests and downloads/uploads files.
Server: Stores and shares files upon request.
---
2. Objectives of FTP
To enable users to transfer files reliably and efficiently.
To provide a method for sharing data between computers.
To allow remote access to files and directories.
To ensure security (with authentication).
---
3. Working Principle
FTP uses two separate TCP connections:
1. Control Connection (Port 21)
Established between the client and server.
Used to send commands and responses.
Remains open throughout the session.
2. Data Connection (Port 20 or dynamic port)
Used to actually transfer files.
Opened when a file transfer command is issued.
Can be closed after the transfer is done.
---
4. Modes of FTP
1. Active Mode:
Server initiates the data connection to the client.
Control: Client → Server (Port 21)
Data: Server → Client (Port 20)
2. Passive Mode:
Client initiates both control and data connections.
Used when the client is behind a firewall/NAT.
---
5. FTP Process Flow
1. Client connects to FTP server using TCP on port 21.
2. Authentication: User provides username and password.
3. Navigation: Client browses directories on the server.
4. File Operations:
Upload (PUT command)
Download (GET command)
Delete or rename files.
5. Disconnection: Client ends the session.
---
6. Neat Diagram of FTP
+------------------+ +------------------+
| FTP Client | | FTP Server |
+------------------+ +------------------+
| Control Connection (Port 21) |
|---------------------------------->|
|<----------------------------------|
| Commands & Replies |
| |
| Data Connection (Port 20/Passive)|
|---------------------------------->|
|<----------------------------------|
| File Upload / Download |
| |
+------------------------------------+
---
7. Advantages of FTP
Fast and reliable file transfers.
Supports large file sizes.
Allows batch transfers.
Widely supported across platforms.
---
8. Disadvantages of FTP
Data and credentials sent in plain text (not secure unless using
FTPS/SFTP).
Requires separate ports for control and data.
Older protocol — less secure compared to modern alternatives.
---
