Day 14a – Networking Fundamentals

Today I practiced networking fundamentals + real troubleshooting workflows across:

• Local machine

• EC2 instances

• External targets like google.com, github.com, and custom domains

👉 In a real-world, DevOps-style environment

Why This Matters

Most people learn networking as theory — OSI layers, TCP/IP, protocols — but struggle when something actually breaks.

In real DevOps work, nobody asks:

“What is Layer 4?”

They ask:

“Why is my service down?”

What is OSI?

OSI is a way to understand how networks work in layers.

It stands for Open Systems Interconnection model.

Think of it like a stack of 7 steps your request passes through when you do something like:

Open WhatsApp

WhatsApp Message — What REALLY happens behind the scenes

You send:

“Hey”

1. Your phone prepares the message (Application Layer)

WhatsApp first:

• Converts “Hey” → data (binary)

• Encrypts it (locks it )

👉 Now it becomes a secure message

Meaning:

“I want to send something safely”

2. Message becomes a packet (Transport Layer starts)

Now WhatsApp wraps it like a parcel:

• Who sent it

• Who should receive it

• The encrypted message

👉 This is called a packet

Meaning:

“Package the message properly for delivery”

3. Finding destination (DNS + Network Layer)

Before sending, your phone asks:

“Where is WhatsApp / friend’s server?”

This is like:

• dig google.com

It returns an IP address

Meaning:

“Find the address before sending”

4. Packet travels through internet (Network path)

Now your message moves:

• Phone → WiFi / mobile data

• ISP (internet provider)

• Routers (traffic system)

• WhatsApp server

👉 Like courier hubs delivering a parcel

Meaning:

“Move data across the world”

5. WhatsApp server (middleman)

Server:

• Does NOT read the message

• Only forwards it

👉 It finds your friend’s active device

Meaning:

“Just deliver, didn’t open”

6. Friend receives message

Friend’s phone:

• Gets packet

• Unlocks it (decrypts)

• Shows: “Hey”

7. Confirmation (TCP + reliability)

Friend’s phone sends back:

“Received”

That’s why you see ✔✔ (blue ticks)

Meaning:

“Delivery confirmed”

When WhatsApp sends message:

You (App Layer)
   ↓
Encrypt + Pack (Transport)
   ↓
Find Address (DNS / Network)
   ↓
Travel Internet (Routers)
   ↓
Server (Middleman)
   ↓
Friend (Receive + Decrypt)
   ↓
Confirm

WhatsApp = type → lock → address → travel → deliver → unlock → confirm

This is part 1 of the Networking for DevOps series.

Next: https://90-days-devops-with-shubham.hashnode.dev/day-14b-tcp-and-udp

#90DaysOfDevOps #DevOpsKaJosh #TrainWithShubham