Module Review
In this final layer of the stack, we explored the services that users actually interact with:
- HTTP & HTTPS: The foundation of the web, moving from stateless plaintext to encrypted sessions via TLS.
- DNS: The global phonebook that translates domain names into IP addresses through a hierarchical resolution process.
- DHCP: How devices automatically plug-in and configure themselves without manual IP entry.
- Email Protocols: The “Push” of SMTP for sending and the “Sync” of IMAP for receiving.
- SSH & FTP: Secure remote management versus legacy file transfer, and the transition to encrypted alternatives.
1. Flashcards
2. Cheat Sheet
| Protocol | Port | Function | Key Feature |
|---|---|---|---|
| HTTP | 80 | Web Traffic (Plaintext) | Stateless, Request/Response |
| HTTPS | 443 | Web Traffic (Secure) | Encrypted via TLS |
| DNS | 53 | Domain Resolution | Translates Names to IPs |
| DHCP | 67/68 | Dynamic IP Assignment | DORA Process |
| SMTP | 25/587 | Email Sending | “Push” protocol |
| IMAP | 143/993 | Email Receiving | State synchronization |
| SSH | 22 | Secure Remote Access | Encrypted shell access |
| FTP | 20/21 | File Transfer | Unencrypted (Legacy) |
3. Quick Revision
- Stateless Protocols: HTTP treats every request independently. It relies on cookies or tokens for state.
- DNS Caching: DNS relies heavily on caching at the browser, OS, and ISP levels to reduce global query latency.
- IMAP vs POP3: IMAP syncs the mailbox state across devices, while POP3 downloads and deletes locally.
- Security Shift: We have actively migrated from insecure defaults (HTTP, FTP, Telnet) to encrypted protocols (HTTPS, SFTP, SSH).
- DHCP Leases: IPs are not permanent; they are leased and must be renewed, allowing networks to reclaim unused addresses.
4. Next Steps
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.
You can review the Course Glossary to brush up on terminology.