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Advanced Topic 36 of 50 Computer Networks

FTP and SSH

File transfer and secure remote login protocols.

How it works

FTP, the File Transfer Protocol, transfers files using a control connection on port 21 and separate data connections, in active or passive mode, and sends credentials in plain text. SSH, Secure Shell, provides encrypted remote login, command execution and tunnelling over port 22, authenticating with passwords or public-key pairs; SFTP and SCP transfer files over it. Host keys protect against impersonation.

Step-by-step walkthrough

  1. FTP opens a control connection on port 21.
  2. It transfers files over a second data connection.
  3. FTP sends passwords in plain text, so it is unsafe.
  4. SSH encrypts everything with keys.
  5. SFTP and scp move files securely over SSH.

Where it is used

SSH is the standard for administering servers, running Git over SSH, automation and port forwarding. FTP survives in legacy systems and some hosting.

Common pitfall

Plain FTP exposes passwords and data, and firewalls and NAT complicate its dual connections, so prefer SFTP. SSH risks include weak passwords, leaked private keys and ignoring host-key warnings. Disable password logins, use keys with passphrases, restrict users and keep servers patched. Verify host fingerprints on first connection.

Where it fits in the course

FTP and SSH is topic 36 of 50 in Computer Networks, rated Advanced. It follows Email Protocols. The next topic is CDN.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Computer Networks quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is FTP and SSH?
File transfer and secure remote login protocols. It belongs to Computer Networks and is an advanced-level topic.
Where do people use FTP and SSH?
SSH is the standard for administering servers, running Git over SSH, automation and port forwarding.
What is the most common mistake with FTP and SSH?
Plain FTP exposes passwords and data, and firewalls and NAT complicate its dual connections, so prefer SFTP.
What should I learn before this topic?
Start with Email Protocols, the topic just before it in Computer Networks.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Computer Networks quiz.
Is FTP and SSH hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn FTP and SSH?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to FTP and SSH?
Email Protocols, CDN, HTTPS and TLS are closely connected. The full list is in the related topics section of this page.
What should I study after FTP and SSH?
Continue with CDN, the next topic in Computer Networks.

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