Linux Networking Basics for DevOps Engineers

If you can’t debug the network, you can’t survive in DevOps.

Linux networking is one of those skills that separates beginners from real engineers. Whether you're debugging a failed API, fixing a Kubernetes cluster, or checking server connectivity — these commands are your weapons.

Let’s break them down in a clean, practical, real-world way.

🧠 1. Understand Your Machine (IP & Interfaces)

📌 Command:

ip a

🔍 What it does:

Shows all network interfaces and IP addresses.

🧾 Example Output:

eth0: inet 192.168.1.10/24
lo:   inet 127.0.0.1

🧠 Diagram:

[Your Machine]
   |
   |-- eth0 (192.168.1.10)
   |-- lo   (127.0.0.1)

👉 Shortcut:

hostname -I

🌐 2. Check Connectivity (Ping)

📌 Command:

ping google.com

🔍 What it does:

Checks if your system can reach another server.

🧠 Diagram:

[You] ---> ---> ---> [Google Server]
         (ICMP packets)

👉 Limit packets:

ping -c 4 google.com

🛣️ 3. Routing Table (Where traffic goes)

📌 Command:

ip route

🔍 What it does:

Shows how your system sends traffic.

🧠 Diagram:

Destination        Gateway
0.0.0.0  ----->  192.168.1.1 (Router)

👉 Meaning:

Default traffic goes through your router

🔍 4. DNS Resolution

📌 Command:

nslookup google.com

👉 Better:

dig google.com

🧠 What happens internally:

google.com → DNS Server → IP Address → Connect

🧠 Diagram:

[You] → [DNS Server] → [Google IP]

5. Check Open Ports (Very Important 🔥)

📌 Command:

ss -tuln

🔍 What it shows:

• Open ports

• Running services

🧠 Example:

LISTEN 0 128 0.0.0.0:80

👉 Meaning:

• Port 80 (HTTP) is open

👉 Check specific port:

ss -tuln | grep 80

🔗 6. Test Port Connectivity

📌 Command:

nc -zv google.com 80

🧠 Diagram:

[Your System] ---> [Server:80]
       (Check if open)

👉 Output:

Connection successful

📡 7. Trace Network Path

📌 Command:

traceroute google.com

🔍 What it does:

Shows each hop between you and destination.

🧠 Diagram:

[You]
  ↓
[Router]
  ↓
[ISP]
  ↓
[Google]

👉 Faster alternative:

tracepath google.com

📥 8. Test APIs / Download Data

📌 Command:

curl -I google.com

🔍 What it does:

Fetches HTTP headers (used in API debugging)

👉 Download file:

wget https://example.com/file.zip

📊 9. Monitor Network Traffic

📌 Commands:

iftop
nload
vnstat

🧠 Diagram:

Incoming ↑↓ Outgoing Traffic
   [ Real-time Monitoring ]

🔐 10. Check Which Process is Using a Port

📌 Command:

lsof -i :80

🔍 Use case:

👉 "Which app is running on port 80?"

🧱 11. Firewall Management

📌 Ubuntu:

ufw status

👉 Allow port:

ufw allow 80

📌 CentOS:

firewall-cmd --list-all

⚙️ 12. Restart Network Service

📌 Ubuntu:

sudo systemctl restart networking

📌 CentOS:

sudo systemctl restart network

🔥 Real DevOps Scenario (Important)

👉 Problem: Your app is not accessible.

🧠 Debug Steps:

1. ip a → Check IP

2. ping → Check connectivity

3. ss -tuln → Check port open?

4. lsof -i → Check process

5. curl → Test API

6. ufw status → Firewall issue?

💡 Final Thoughts

Linux networking isn’t about memorizing commands —
it’s about thinking like a system.

Once you understand:

• How packets move

• How DNS resolves

• How ports listen

👉 You can debug almost anything.

Connect With Me 🤝

If you found this article helpful and want to follow my DevOps learning journey, feel free to connect with me on the platforms below where I regularly share DevOps tips, tutorials, and practical learning experiences.

📖 Blog
https://devopsjourneywithrahul.hashnode.dev/

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https://www.instagram.com/devopsjourneywithrahul/

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https://www.youtube.com/@devopsjourneywithrahul

Let's continue learning and growing together in the DevOps journey 🚀

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