FTP Protocol Interactive Learning Module

What is FTP?

The File Transfer Protocol (FTP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network.

Purpose & Existence

FTP was developed in the early 1970s (RFC 114) to enable reliable data exchange across diverse systems. It solves the problem of file incompatibility and provides a structured way to navigate remote file systems.

Port 21: Control Connection (Commands)
Port 20: Data Connection (File transfer)

The FTP Handshake & Connection

FTP is unique because it uses two separate channels.

Client

↔

Server

> Click the button to start the connection simulation...

FTP Message & Command Types

FTP communicates via plain-text commands and numeric status codes.

1. Authentication Commands (USER/PASS)

Used to identify the user and verify their credentials. Click to see example.

2. Transfer Mode (TYPE)

Defines if the file is ASCII (text) or Image (binary). Click to see example.

3. File Actions (RETR/STOR)

RETR retrieves a file from server; STOR uploads a file. Click to see example.

The Anatomy of an FTP Packet

Since FTP operates at the Application Layer, it doesn't have a bit-level binary header like TCP/IP. Instead, it relies on the TCP header for transport. The "header" in FTP terms is the Command/Response structure.

TCP Segment Data Area (The FTP Payload)

Command (4-Chars)

Space

Arguments / Parameters

CRLF (\r\n)

Field Breakdown

Command: A 3 or 4 character string (e.g., LIST, QUIT).
Arguments: Variable length, specifies paths or options.
CRLF: Hex 0x0D 0x0A, signals the end of a command.

Interactive FTP Command Builder

Construct a valid FTP command and see how it is formatted for the wire.

Select Action:

FTP Protocol Deep Dive