The OSI Model: Key Layers Explained

As I continue building a strong foundational base in DevOps, today I explored the OSI Model—a conceptual framework that standardizes how different networking systems communicate.

📦 What is the OSI Model?

The OSI (Open Systems Interconnection) Model is a 7-layer framework designed by the ISO to help understand and design a universal standard for networking.

Each layer describes a different function in the process of transmitting data over a network.

🔍 The 7 Layers of the OSI Model

Layer	Name	Function	Common Protocols / Devices
7	Application	Interfaces directly with the end-user's software	HTTP, HTTPS, FTP, SMTP, DNS
6	Presentation	Data translation, encryption, compression	SSL/TLS, JPEG, ASCII, MPEG
5	Session	Manages sessions (start, maintain, end)	NetBIOS, PPTP, RPC
4	Transport	Reliable delivery, flow and error control	TCP (reliable), UDP (fast, no guarantee)
3	Network	Routing, logical addressing	IP, ICMP, IPSec, IGMP
2	Data Link	Physical addressing (MAC), error detection	Ethernet, PPP, Frame Relay, MAC address
1	Physical	Transmitting raw bits via cables/wireless	Ethernet cables, Fiber optics, Wi-Fi, Hubs

🎯 Why DevOps Engineers Should Know This?

Helps in troubleshooting (e.g., ping = layer 3, telnet = layer 7).
Critical for configuring firewalls, VPNs, proxies, load balancers.
Assists with packet flow, port management, and security configurations.

📌 Example Mapping:

When you send an HTTP request:
- It’s initiated at Layer 7 (Application).
- Broken into segments at Layer 4 (Transport).
- Routed at Layer 3 (Network).
- Sent as frames on Layer 2, and as bits on Layer 1.

📚 Mnemonics to Remember:

Top to Bottom:

"All People Seem To Need Data Processing"
Bottom to Top:
"Please Do Not Throw Sausage Pizza Away"

📅 Next Up (Day 32):
Classification of Computer Networks by Geography

Day 31 - Simplifying the OSI Model: Key Layers Explained