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Himanshu Bhatt
Himanshu Bhatt

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Networking 101 #3. IP Addresses & Ports

#networking #tutorial #beginners #devops

👋 Short Intro (Why I’m Writing This)

I’m currently learning Networking for DevOps and decided to learn in public by documenting my journey.

This blog is part of my Networking 101 series, where I’m learning Networking for DevOps step by step from scratch.

This series is not written by an expert — it’s a beginner learning out loud, sharing:

  • what I understand,
  • what confuses me,
  • and what I learn along the way.

The goal is to build consistency, clarity, and invite discussion.

📌 What This Blog Covers

In this post, I’ll cover:

  • IP Address, Local IP vs Internet IP
  • Public IP vs Private IP
  • Brief overview of NAT
  • Ports
  • localhost vs 127.0.0.1
  • Few Basic commands

📂 GitHub Repository

All my notes, diagrams, and learning resources for this series live here:

👉 GitHub Repo:

https://github.com/dmz-v-x/networking-for-devops-101

This repo is updated as I continue learning.

📚 Learning Notes

1. What is an IP address (really)?

An IP address identifies a machine on a network.

That’s it.

Just remember this:

IP address = identity of a machine on a network

Examples:

192.168.1.10
10.0.0.5
13.234.56.78
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Every machine that communicates on a network must have an IP.

2. Local IP vs Internet IP (very first distinction)

Your laptop has:

  • One IP inside your local network
  • Possibly another IP visible to the internet

Why? Because networks are layered.

Example:

Laptop → WiFi Router → Internet
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Your laptop is not directly exposed to the internet.

3. Public IP Address (Internet-facing)

A public IP:

  • Is unique on the internet
  • Can be accessed from anywhere
  • Is assigned by ISPs or cloud providers

Example:

13.234.56.78
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Cloud servers usually have:

  • A public IP (optional)
  • A private IP (always)

4. Private IP Address (Internal-only)

A private IP:

  • Works only inside a private network
  • Cannot be reached directly from the internet

Common private IP ranges:

10.0.0.0    – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255
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Your home WiFi, office network, and cloud VPCs all use private IPs.

5. Why private IPs exist

The internet does not have enough IPs for every device.

So:

  • Private IPs are reused everywhere
  • Public IPs act as gateways

This design allows:

  • Security (not everything exposed)
  • Scalability
  • Cost efficiency

This leads us to a very important idea (we’ll learn this concept later):
👉 NAT (Network Address Translation)

6. Tiny preview: What NAT does

NAT allows:

Many private IPs → One public IP
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Your laptop sends traffic:

192.168.1.10 → Internet
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The router translates it to:

Public IP → Internet
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7. What is a port?

If an IP identifies a machine, a port identifies a program on that machine.

One machine can run many applications:

  • Web server
  • Database
  • SSH
  • Cache

Ports make this possible.

8. Port analogy (simple but powerful)

Think of:

  • IP address → apartment building
  • Port → apartment number 
13.234.56.78:22   → SSH
13.234.56.78:80   → HTTP
13.234.56.78:443  → HTTPS
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Same building, different doors.

9. Common ports every DevOps engineer must know

Port Purpose
22 SSH
80 HTTP
443 HTTPS
3306 MySQL
5432 PostgreSQL
6379 Redis

10. How IP + Port work together

A network connection always needs:

IP address + Port
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Examples:

ssh user@13.234.56.78     → port 22
https://example.com       → port 443
localhost:3000            → port 3000
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Without a port, the OS doesn’t know which app should receive the data.

11. localhost vs 127.0.0.1

When we run an application on our laptop, that's when localhost and 127.0.0.1 comes into picture.

11.1 What is 127.0.0.1?

127.0.0.1 is an IP address, specially it is called loopback IP which means if any network request sent to this IP it comes back to the same machine.

The request never leaves our machine, no router, no internet and no external network is involved.

11.2 What is localhost?

localhost is a hostname, it's not an ip. When we type localhost our operating system translates this name into an IP address that is 127.0.0.1

localhost → 127.0.0.1

This translation happens via

  • /etc/hosts file (Linux/macOS)
  • C:\Windows\System32\drivers\etc\hosts (Windows)

11.3 How does localhost actuallly works?

When we type: http://localhost:3000, internally our operating system follow these steps:

  • OS sees localhost
  • It looks up the hosts file
  • Resolve it to an IP (usually 127.0.0.1)
  • Send the request to that IP

So the flow becomes:

localhost → 127.0.0.1 → your own machine

11.4 Are localhost and 127.0.0.1 same?

Short Answer: No

  • 127.0.0.1 is hard-coded as a loopback IP
  • localhost is configurable

Our system can map localhost to something else

In many modern systems:

localhost → ::1

::1 is the IPv6 loopback address.

11.4 Which one should we use?

Use localhost when:

  • Developing locally
  • You don't care about IPv4 vs IPv6

Use 127.0.0.1 when:

  • Debugging networking issues
  • Want guaranteed IPv4
  • Dealing with Docker, databases, or binding issues

11.5 A DevOps Example:

If our server logs say:

Listening on 127.0.0.1

That means:

  • Only this machine can access it.
  • Not accessible from other devices.

If it listens on:

0.0.0.0

That means:

  • Accept connections from any network interface.

11.6 Complete flow 

We type in browser:
   `localhost`
       ↓
 OS resolves name
       ↓
   `127.0.0.1` or ::1
       ↓
 Request comes back to
   your own machine
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12. Classic DevOps failure example

Problem:

App works on your laptop but not on the cloud server.

What’s happening:

  • App is listening on localhost
  • Cloud traffic comes to public IP
  • App never sees it

Fix:

  • Bind app to 0.0.0.0
  • Open the correct port
  • Allow traffic in firewall/security group

We’ll fully break this down later.

13. Hands-on commands

13.1 Check your IPs 

ip addr        # Linux
ifconfig       # macOS
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13.2 See listening ports 

ss -tuln
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or

netstat -tuln
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13.3 Test remote port 

nc -vz 13.234.56.78 443
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✅ Key takeaways

  • IP address identifies a machine
  • Port identifies an application
  • Public IP → internet-facing
  • Private IP → internal-only
  • localhost vs 127.0.0.1
  • Most DevOps bugs = wrong IP, wrong port, or wrong binding

💬 Feedback & Discussion

💡 I’d love your feedback!

If you notice:

  • missing tool categories,
  • incorrect assumptions,
  • or better learning paths,

please comment below. I’m here to learn.

⭐ Support the Learning Journey

If you found this blog useful:

⭐ Consider giving the GitHub repo a star —

it really motivates me to keep learning and sharing publicly.

🐦 Stay Updated (Twitter / X)

I share learning updates, notes, and progress regularly.

👉 Follow me on Twitter/X:

https://x.com/_himanshubhatt1

🔜 What’s Next

In the next post, I’ll be covering:

👉 TCP vs UDP (Connections, Reliability, and Why It Matters)

I’ll also continue updating the GitHub repo as I progress.

📘 Learning in public

📂 Repo: https://github.com/dmz-v-x/networking-for-devops-101
🐦 Twitter/X: https://x.com/_himanshubhatt1
💬 Feedback welcome — please comment if anything feels off
⭐ Star the repo if you find it useful

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