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TCP/IP Model

Learn the 4-layer TCP/IP stack that powers the real internet

15 min+41 XP3 quiz
Module progress2 of 4
ApplicationTransportInternetNetwork AccessEncapsulation ↓
Four TCP/IP layers · Encapsulation flow

Opening

OSI is the textbook. TCP/IP is the internet.

You learned the seven-layer OSI model—a perfect teaching tool. But the actual internet runs on TCP/IP, a simpler four-layer stack developed for ARPANET and still used today. Every packet you capture in Wireshark, every firewall rule you write, and every Nmap scan you run speaks TCP/IP.

1. The 4 TCP/IP Layers

  • Link (Network Access)

    Combines OSI Layers 1 and 2. Handles physical transmission and local delivery via MAC addresses and Ethernet frames.

  • Internet

    Maps to OSI Layer 3. IP addresses, routing, and ICMP (ping). This layer gets packets across networks.

  • Transport

    Maps to OSI Layer 4. TCP provides reliable, ordered delivery; UDP is connectionless and fast. Ports live here.

  • Application

    Combines OSI Layers 5, 6, and 7. HTTP, DNS, SSH, SMTP—all the protocols users and apps actually use.

2. OSI vs TCP/IP — Side by Side

Think of OSI as seven detailed drawers and TCP/IP as four bigger bins that hold the same stuff: OSI Physical + Data Link = TCP/IP Link OSI Network = TCP/IP Internet OSI Transport = TCP/IP Transport OSI Session + Presentation + Application = TCP/IP Application

3. Security Relevance by Layer

  • Link layer

    ARP cache poisoning, rogue access points, and switch attacks happen before IP is even involved.

  • Internet layer

    IP spoofing, DDoS via ICMP, and geofencing/blocklists all operate on IP addresses.

  • Transport layer

    Firewalls filter TCP/UDP ports. Scanners like Nmap probe open ports to find vulnerable services.

  • Application layer

    Web app attacks, credential theft, and C2 (command-and-control) traffic hide in HTTP, DNS, and TLS.

TCP vs UDP in one sentence

TCP is like a phone call—connected, confirmed, retransmits if something drops. UDP is like shouting across a room—fast, no guarantee. Video streaming and DNS often use UDP; web browsing and file transfer use TCP.

Knowledge Check

1

How many layers does the TCP/IP model have?

Multiple choice

Knowledge Check

2

Which TCP/IP layer corresponds to OSI Layer 3 (Network)?

Multiple choice

Knowledge Check

3

True or False: The TCP/IP Application layer covers HTTP, DNS, and SSH.

True or False

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Answer all 3 knowledge checks to continue. (0/3 answered)

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