🚀 Day 42: OSI & TCP/IP Models in Practice

Today I explored two fundamental networking models that every DevOps & Cloud Engineer must understand:

• OSI (Open Systems Interconnection) Model

• TCP/IP (Transmission Control Protocol / Internet Protocol) Model

Along with theory, I also practiced important hands-on networking commands.

🧠 Conceptual Understanding

🔹 OSI Model – 7 Layers

1. Physical Layer → Deals with hardware, cables, signals, binary transmission.

2. Data Link Layer → Ensures error-free delivery between nodes (MAC addresses, switches).

3. Network Layer → Handles logical addressing & routing (IP addresses, routers).

4. Transport Layer → Ensures reliable delivery (TCP/UDP, ports).

5. Session Layer → Manages communication sessions.

6. Presentation Layer → Data formatting, encryption, compression.

7. Application Layer → End-user interaction (HTTP, FTP, DNS).

🔹 TCP/IP Model – 4 Layers

1. Link Layer → Physical + Data Link (Ethernet, Wi-Fi).

2. Internet Layer → Network (IP, ICMP).

3. Transport Layer → TCP, UDP.

4. Application Layer → HTTP, DNS, SSH, etc.

📌 Key Difference:

• OSI is a theoretical reference model.

• TCP/IP is practical & widely used on the internet.

🛠️ Hands-on Practice

I used common Linux networking tools to connect theory with practice:

1️⃣ ping – Check connectivity

ping google.com

• Sends ICMP echo requests.

• Helps verify if a host is reachable.

2️⃣ traceroute – Track packet path

traceroute google.com

• Shows all intermediate hops between source & destination.

• Useful to troubleshoot latency & routing issues.

3️⃣ netstat – Network statistics

netstat -tulnp

• Displays open ports, listening services, and connections.

4️⃣ ss – Modern alternative to netstat

ss -tulnp

• Faster and more detailed than netstat.

5️⃣ nmap – Network mapper

nmap -sV localhost

• Scans open ports & identifies services running.

• Used for security auditing.

🔎 Reflection

• The OSI/TCP-IP models gave me a structured way to think about networking.

• The hands-on commands showed me how to observe real traffic on my machine.

• Now I understand how theory maps to practical tools in DevOps & Cloud.

👨‍💻 Author

Ritesh Singh
🌐 LinkedIn | 📝 Hashnode | GitHub

#100DaysOfDevOps #CICD #GitHubActions #DevOps #Beginner #networking #OSI #TCP/IP