FTP and SFTP for file transfer in Computer Networks - Step-by-Step Execution

Concept Flow - FTP and SFTP for file transfer

Start: User wants to transfer files

↓

Choose Protocol: FTP or SFTP

↓

FTP Protocol

↓

Connect to Server

↓

Send Commands

↓

Transfer Files

↓

Close Connection

↓

End

User chooses FTP or SFTP to connect to a server, send commands, transfer files, then close the connection.

Execution Sample

Computer Networks

Connect to server using FTP
Login with username and password
Send command to upload file
File transfers over network
Close FTP connection

This shows the basic steps of transferring a file using FTP.

Analysis Table

Step	Action	Protocol	Result	Notes
1	User initiates connection	FTP	Connection established	Server accepts FTP connection on port 21
2	User logs in	FTP	Login successful	Username and password sent in plain text
3	User sends upload command	FTP	Server ready to receive file	Command: STOR filename
4	File data sent	FTP	File transferred	Data sent over separate data connection
5	Connection closed	FTP	Session ended	User disconnects
6	User initiates connection	SFTP	Connection established	Server accepts SFTP connection on port 22
7	User authenticates	SFTP	Login successful	Authentication encrypted via SSH
8	User sends upload command	SFTP	Server ready to receive file	Command sent over encrypted channel
9	File data sent	SFTP	File transferred	Data encrypted during transfer
10	Connection closed	SFTP	Session ended	User disconnects securely

💡 File transfer completes and connection closes for both FTP and SFTP

State Tracker

Variable	Start	After FTP Login	After FTP Upload	After FTP Close	After SFTP Login	After SFTP Upload	After SFTP Close
Connection Status	Disconnected	Connected	Connected	Disconnected	Connected	Connected	Disconnected
Authentication	None	Plain text	Plain text	None	Encrypted	Encrypted	None
File Transfer Status	Not started	Not started	In progress	Completed	Not started	In progress	Completed

Key Insights - 3 Insights

Why is FTP considered less secure than SFTP?

FTP sends login details and file data in plain text (see execution_table rows 2 and 4), making it easy to intercept. SFTP encrypts all data (rows 7 and 9), protecting information.

Why does FTP use two connections while SFTP uses one?

FTP opens a separate data connection for file transfer (row 4), while SFTP transfers commands and data over a single encrypted SSH connection (rows 8 and 9).

What happens if the connection is lost during file transfer?

The transfer stops and the session ends without completing the file upload (implied by exit_note). Both protocols require reconnecting to resume.

Visual Quiz - 3 Questions

Look at the execution_table at step 2 for FTP. What is the security status of the login?

A Login details are sent encrypted

B Login details are sent in plain text

C No login is required

D Login uses a token

💡 Hint

Check the 'Notes' column for step 2 in the execution_table

At which step does SFTP start transferring the file data?

A Step 9

B Step 8

C Step 7

D Step 10

💡 Hint

Look for 'File data sent' action under SFTP in the execution_table

If FTP used encryption like SFTP, which variable in variable_tracker would change after login?

A Connection Status

B File Transfer Status

C Authentication

D None

💡 Hint

Check the 'Authentication' variable values before and after login in variable_tracker

Concept Snapshot

FTP and SFTP are protocols to transfer files over a network.
FTP uses two connections and sends data unencrypted.
SFTP uses one encrypted connection via SSH.
SFTP is more secure and preferred for sensitive data.
Both require login and support commands to upload/download files.

Full Transcript

This visual execution trace shows how FTP and SFTP protocols work for file transfer. The user starts by choosing a protocol, then connects to the server. FTP connects on port 21 and sends login details in plain text, while SFTP connects on port 22 and encrypts all communication. Both protocols send commands to upload files and transfer data, but FTP uses a separate data connection and SFTP uses a single encrypted channel. After file transfer, the connection closes. The variable tracker shows connection status, authentication method, and file transfer progress at each step. Key moments highlight FTP's lack of security, the difference in connection usage, and what happens if connection is lost. The quiz tests understanding of login security, file transfer steps, and authentication changes. The snapshot summarizes the main points: FTP is older and less secure, SFTP is encrypted and safer for file transfers.

Practice

1. Which of the following statements correctly describes the main difference between FTP and SFTP?

easy

A. Neither FTP nor SFTP encrypt data during transfer.

B. SFTP encrypts data during transfer, while FTP does not.

C. Both FTP and SFTP encrypt data equally.

D. FTP encrypts data during transfer, while SFTP does not.

Solution

1. Step 1: Understand FTP security

   FTP is an older protocol that transfers files without encryption, making data vulnerable to interception.

2. Step 2: Understand SFTP security

   SFTP uses encryption to protect data during transfer, making it secure over untrusted networks.

3. Final Answer:

   SFTP encrypts data during transfer, while FTP does not. -> Option B

4. Quick Check:

   Encryption difference = SFTP encrypts, FTP does not [OK]

Hint: Remember: S in SFTP means Secure [OK]

Common Mistakes:

• Thinking FTP encrypts data
• Assuming both protocols are equally secure
• Confusing FTP with FTPS (which adds SSL)

2. Which of the following is the correct command to connect to a server using SFTP in a terminal?

easy

A. ftp [e-mail]

B. ssh [e-mail]

C. scp [e-mail]

D. sftp [e-mail]

Solution

1. Step 1: Identify SFTP command syntax

   The command to start an SFTP session is sftp [e-mail], which initiates a secure file transfer connection.

2. Step 2: Differentiate from other commands

   ftp is for FTP connections, ssh is for remote shell access, and scp copies files but is not an interactive file transfer session.

3. Final Answer:

   sftp [e-mail] -> Option D

4. Quick Check:

   SFTP command starts with 'sftp' [OK]

Hint: SFTP command always starts with 'sftp' [OK]

Common Mistakes:

• Using 'ftp' instead of 'sftp' for secure transfer
• Confusing SSH with SFTP command
• Using SCP which is not interactive

3. Consider this Python snippet using the paramiko library to upload a file via SFTP:

import paramiko
client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
client.connect('example.com', username='user', password='pass')
sftp = client.open_sftp()
sftp.put('local.txt', 'remote.txt')
sftp.close()
client.close()

What will happen when this code runs successfully?

medium

A. The file 'local.txt' is uploaded securely to 'remote.txt' on the server.

B. The file 'remote.txt' is downloaded to 'local.txt' on the client.

C. An error occurs because paramiko does not support SFTP.

D. The connection is made but no file transfer happens.

Solution

1. Step 1: Understand paramiko SFTP usage

   The code connects to the server using SSH, then opens an SFTP session to transfer files securely.

2. Step 2: Analyze the sftp.put method

   sftp.put('local.txt', 'remote.txt') uploads the local file named 'local.txt' to the server as 'remote.txt'.

3. Final Answer:

   The file 'local.txt' is uploaded securely to 'remote.txt' on the server. -> Option A

4. Quick Check:

   sftp.put uploads local to remote [OK]

Hint: sftp.put uploads local file to server [OK]

Common Mistakes:

• Confusing upload with download (put vs get)
• Thinking paramiko does not support SFTP
• Assuming no file transfer happens without error

4. A user tries to connect to a server using SFTP but gets an error: Permission denied (publickey). What is the most likely cause?

medium

A. The SFTP command is not installed on the client machine.

B. The user typed the wrong server address.

C. The server requires a public key for authentication, but the user did not provide one.

D. The file transfer was interrupted by network issues.

Solution

1. Step 1: Interpret the error message

   Permission denied (publickey) means the server expects a public key for login but did not accept any provided or none was given.

2. Step 2: Rule out other causes

   Wrong server address or missing SFTP command would cause different errors. Network interruption would not cause a permission denied error.

3. Final Answer:

   The server requires a public key for authentication, but the user did not provide one. -> Option C

4. Quick Check:

   Public key error means missing or wrong key [OK]

Hint: Permission denied (publickey) means missing SSH key [OK]

Common Mistakes:

• Assuming network issues cause permission denied
• Thinking the command is missing on client
• Confusing server address errors with authentication errors

5. You need to securely transfer multiple files from your local machine to a remote server over an untrusted network. Which approach is best to ensure security and efficiency?

hard

A. Use SFTP to transfer files directly with encryption.

B. Use FTP with a VPN connection to encrypt the data.

C. Use FTP without encryption because it's faster.

D. Use HTTP to upload files through a web browser.

Solution

1. Step 1: Evaluate security needs

   Since the network is untrusted, encryption is necessary to protect data during transfer.

2. Step 2: Compare transfer methods

   SFTP provides built-in encryption and secure authentication, making it ideal for secure file transfer. FTP alone is not secure, even with VPN it adds complexity. HTTP is not designed for secure file transfer.

3. Final Answer:

   Use SFTP to transfer files directly with encryption. -> Option A

4. Quick Check:

   SFTP = secure and efficient file transfer [OK]

Hint: Choose SFTP for secure file transfer over untrusted networks [OK]

Common Mistakes:

• Relying on FTP without encryption
• Assuming VPN always solves FTP security
• Using HTTP which is not meant for file transfer