Day 14c –Where HTTP, TCP, IP Actually Sit (Layer Mapping Simplified)
Day 14c – OSI vs TCP/IP + Protocol Mapping
This is Part 3 of the Networking for DevOps series.
In the previous part, we understood https://90-days-devops-with-shubham.hashnode.dev/day-14b-tcp-and-udp
Core Concepts
OSI vs TCP/IP (In Simple Words)
OSI (7 layers) → Conceptual framework for understanding networking
(Physical → Data Link → Network → Transport → Session → Presentation → Application)
L7 Application → User-facing protocols (HTTP, DNS, FTP)
L6 Presentation → Data formatting, encryption concepts (mapped to application layer in TCP/IP)
L5 Session → Manages communication sessions between systems
L4 Transport → TCP (reliable), UDP (fast)
L3 Network → IP addressing & routing
L2 Data Link → MAC, Ethernet frames
L1 Physical → Cables, Wi-Fi signals
Mapping:
| OSI Layer (7) | OSI Layer Name | TCP/IP Layer (4) | Key Concepts / Protocols |
|---|---|---|---|
| 7 | Application | Application | HTTP, HTTPS, FTP, SMTP, DNS |
| 6 | Presentation | Application | SSL/TLS, Encryption, Compression |
| 5 | Session | Application | Session Management |
| 4 | Transport | Transport | TCP, UDP |
| 3 | Network | Internet | IP, ICMP, IPSec |
| 2 | Data Link | Network/Link | Ethernet, VLAN, MAC (ARP bridges L2–L3) |
| 1 | Physical | Network/Link | Cables, NIC, Signals, WiFi |
TCP/IP (4 layers) → Practical model used in real networks
Link → Internet → Transport → Application
| OSI Layers | TCP/IP Layer | Examples |
|---|---|---|
| L7–L5 | Application | HTTP, HTTPS, DNS, TLS |
| L4 | Transport | TCP, UDP |
| L3 | Internet | IP, ICMP |
| L2-L1 | Link | Ethernet, Wi-Fi |
Key Difference:
OSI is for learning;
TCP/IP is what actually runs the internet.
Protocol Placement - Where Things Sit
Where IP, TCP/UDP, HTTP/HTTPS, DNS sit in the stack
| Protocol | Layer |
|---|---|
| IP | Internet Layer (OSI L3) |
| TCP/UDP | Transport Layer (OSI L4) |
| HTTP,HTTPS,DNS | Application Layer |
| DNS | Application Layer (uses UDP/TCP 53) |
Example:
curl https://www.google.com = App layer over TCP over IP
Layer 7 (Application): curl creates the HTTP request (GET /index.html).
Layer 6 (Presentation): Encrypts the data with SSL/TLS (handled within application layer in TCP/IP model).
Layer 5 (Session): Manages connection state (handled mostly by application/TCP in real systems)
Layer 4 (Transport): Wraps in TCP for reliability (Port 54321 -> 443).
Layer 3 (Network): Adds IP addressing (Src: 192.168.1.100 -> Dst: 93.184.216.43).
Layer 2 (Data Link): Adds MAC addresses for the local router.
Layer 1 (Physical): onverts data into electrical signals or radio waves for transmission
This is:
Application (HTTP)
↓
Transport (TCP)
↓
Internet (IP)
↓
Link (MAC/ARP)
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