🔗 Networking in Linux for DevOps: A Complete Guide

📌 Why is Networking Important in DevOps?

In a DevOps environment, applications, containers, and cloud services must communicate efficiently. Networking plays a key role in:
✅ Cloud & Infrastructure – AWS, Azure, GCP rely on networking for VPCs, Load Balancers, and Security Groups.
✅ Containers & Kubernetes – Services inside Docker & Kubernetes communicate over networks.
✅ CI/CD Pipelines – Secure network connections are required for pulling repositories, testing, and deploying applications.
✅ Monitoring & Security – Logging, monitoring, and security tools need proper network configurations.

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1️⃣ Understanding Basic Networking Concepts

Before jumping into Linux commands, let’s understand some networking fundamentals:

📍 IP Addressing & Subnetting – Every machine on a network needs an IP. Example: 192.168.1.10/24
📍 Routing – Determines how data moves between different networks.
📍 DNS (Domain Name System) – Resolves domain names to IP addresses. Example: google.com → 142.250.182.206
📍 Ports & Protocols – Communication happens over TCP & UDP ports. Example: HTTP (80), HTTPS (443), SSH (22).

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2️⃣ Essential Linux Networking Commands 🛠️

🔹 Check Network Configuration

ip a

Shows IP addresses assigned to all network interfaces.

🔹 Check Network Routes

ip route

Displays how packets travel in the network.

🔹 Check Active Network Connections

netstat -tulnp   # Shows open ports  
ss -tunlp        # Faster alternative to netstat  

🔹 Test Network Connectivity

ping google.com    # Checks if a host is reachable  
traceroute google.com   # Shows the path of packets through networks  

🔹 Find DNS Resolution

nslookup google.com

or

dig google.com

Resolves a domain to an IP address.

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3️⃣ Managing Network Interfaces in Linux 🌐

🔹 Enable & Disable Network Interfaces

ip link set eth0 up      # Enable interface  
ip link set eth0 down    # Disable interface  

🔹 Assign a Static IP Address

ip addr add 192.168.1.100/24 dev eth0

🔹 Restart Network Services (for older systems)

systemctl restart networking   # For systemd-based systems  
service network restart         # For older Linux distributions  

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4️⃣ Firewalls & Network Security in Linux 🔥

Linux firewalls protect servers from unauthorized access. Two main firewall tools:

📍 iptables (Legacy) – Command-line firewall tool.
📍 firewalld (Modern) – More user-friendly and dynamic firewall management.

🔹 Check Existing Firewall Rules

iptables -L -v -n   # Shows current rules  
firewall-cmd --list-all   # For firewalld  

🔹 Allow/Block a Specific Port (Example: SSH - Port 22)

iptables -A INPUT -p tcp --dport 22 -j ACCEPT   # Allow SSH  
iptables -A INPUT -p tcp --dport 22 -j DROP     # Block SSH  

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5️⃣ Load Balancing & Traffic Routing in Linux 🚦

Load balancing helps distribute traffic among multiple servers.

🔹 Nginx as a Load Balancer

nginx

upstream backend {
    server backend1.example.com;
    server backend2.example.com;
}
server {
    listen 80;
    location / {
        proxy_pass http://backend;
    }
}

This config distributes traffic between backend1 and backend2.

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6️⃣ Secure Remote Access & SSH Hardening 🔐

Since DevOps engineers work remotely on servers, secure SSH access is crucial.

🔹 Basic SSH Commands

ssh user@server_ip   # Connect to remote server  
scp file.txt user@server:/home/user/  # Copy files to remote server  

🔹 Disable Root Login & Use Key-Based Authentication
Edit SSH config:

sudo nano /etc/ssh/sshd_config

Set:

PermitRootLogin no
PasswordAuthentication no

Then restart SSH:

systemctl restart sshd

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🎯 Conclusion: Why Linux Networking Matters in DevOps?

✅ Helps troubleshoot infrastructure & deployment issues
✅ Improves security of cloud environments & applications
✅ Optimizes traffic flow for better application performance
✅ Essential for Kubernetes, Docker, CI/CD, and Cloud Networking

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