Module Review

In this final layer of the stack, we explored the services that users actually interact with:

  1. HTTP & HTTPS: The foundation of the web, moving from stateless plaintext to encrypted sessions via TLS.
  2. DNS: The global phonebook that translates domain names into IP addresses through a hierarchical resolution process.
  3. DHCP: How devices automatically plug-in and configure themselves without manual IP entry.
  4. Email Protocols: The “Push” of SMTP for sending and the “Sync” of IMAP for receiving.
  5. SSH & FTP: Secure remote management versus legacy file transfer, and the transition to encrypted alternatives.

1. Flash Quiz

1. Which HTTP status code indicates that a resource was not found?

  • 404 Not Found.

2. What is the difference between a Recursive and an Iterative DNS query?

  • In a Recursive query, the server does the hard work of finding the answer for you; in an Iterative query, the server just gives you a referral to the next server in the hierarchy.

3. What does DORA stand for in DHCP?

  • Discover, Offer, Request, Acknowledgement.

4. Why is IMAP preferred over POP3?

  • IMAP syncs the state (folders, read status) across multiple devices, while POP3 usually downloads and deletes mail from the server.

5. Which port is the standard for secure remote shell access (SSH)?

  • Port 22.

2. What’s Next?

We have traversed the entire OSI Model! In the following modules, we will look at how all these layers come together to address modern challenges: Network Security, Cloud Networking, and Troubleshooting.