devops-notes/04_Linux_Networking_Basics.md

Linux – Networking Basics (Day 4)

What is Networking in Linux?

Networking means how computers and servers communicate with each other using IP addresses, ports, and protocols.

Every DevOps engineer must understand networking because applications run on networks.

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Why Networking is Important for DevOps?

If networking fails:

• app will not open
• server looks “down”
• deployment fails

Most DevOps issues are actually network issues.

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IP Address

An IP address identifies a machine on a network.

Check IP:

ip a

or

ifconfig

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Hostname

hostname

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Ping Command

ping google.com

Stop ping:

Ctrl + C

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curl Command (VERY IMPORTANT)

curl google.com
curl -I google.com

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wget Command

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

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Ports (CRITICAL CONCEPT)

Common ports:

• 22 → SSH
• 80 → HTTP
• 443 → HTTPS
• 3306 → MySQL

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Check Open Ports

netstat -tuln

or

ss -tuln

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Check Which Process Uses a Port

sudo netstat -tulnp

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DNS Resolution

nslookup google.com
dig google.com

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Test Server Connectivity

telnet google.com 80

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Real DevOps Scenario

Commands used:

curl
ping
netstat
ss

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Common Mistakes

• Forgetting port number
• Confusing localhost and public IP

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DevOps Rule

If something doesn’t work → check network first.

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Summary

Linux networking basics: IP, ports, ping, curl, DNS, and open ports.