Lesson 09 — Linux Networking

Lesson Overview

Almost every Linux server communicates with other systems over a network.

Whether you’re:

Accessing a website
Connecting to an AWS EC2 instance using SSH
Deploying Kubernetes clusters
Downloading software updates
Accessing cloud storage
Connecting to a database

Linux networking makes it all possible.

As a Cloud Engineer, DevOps Engineer, Linux Administrator, or Cybersecurity Professional, you’ll spend a significant amount of your time troubleshooting network connectivity, configuring interfaces, verifying DNS resolution, and monitoring traffic.

In this lesson, you’ll learn the Linux networking fundamentals that are used daily in enterprise environments.

Learning Objectives

After completing this lesson, you will be able to:

Understand Linux network interfaces.
View and configure IP addresses.
Understand routing and gateways.
Configure DNS.
Test network connectivity.
Troubleshoot networking issues.
Use common Linux networking commands.

Linux Networking Overview

Every Linux server connects to a network using one or more Network Interfaces.

A network interface allows Linux to send and receive data.

Example:

Linux Server

↓

Network Interface

↓

Switch

↓

Router

↓

Internet

Without a network interface, a server cannot communicate with other devices.

Network Interfaces

Modern Linux systems use predictable interface names.

Common examples:

eth0

ens33

ens160

enp0s3

wlan0

Cloud platforms often use names such as:

ens5

eth0

Viewing Network Interfaces

Display all interfaces.

ip link show

ip link

Example output:

lo

ens33

Viewing IP Addresses

Display IP configuration.

ip addr

ip a

Example:

ens33

192.168.1.100/24

This command replaces the older ifconfig utility.

Understanding IP Address Information

Example:

192.168.1.100/24

Where:

192.168.1.100 = IP Address
/24 = Subnet Prefix

This identifies the host on the local network.

Loopback Interface

Linux always includes the Loopback Interface.

lo

Loopback IP:

127.0.0.1

Purpose:

Local communication
Application testing
Service verification

Viewing Routing Information

Display routing table.

ip route

Example:

default via 192.168.1.1

The default gateway sends traffic destined for external networks.

Default Gateway

The default gateway forwards traffic outside the local network.

Example:

Linux Server

↓

Gateway

192.168.1.1

↓

Internet

Without a default gateway, Internet connectivity is not possible.

DNS Configuration

Linux stores DNS configuration in:

/etc/resolv.conf

Example:

nameserver 8.8.8.8

Display DNS settings.

cat /etc/resolv.conf

Hostname Configuration

Display hostname.

hostname

Display detailed hostname information.

hostnamectl

Change hostname.

sudo hostnamectl set-hostname web-server

Testing Connectivity

Ping another device.

ping google.com

Ping an IP address.

ping 8.8.8.8

Successful replies indicate network connectivity.

Tracing Network Paths

View the path packets take.

Ubuntu:

traceroute google.com

If not installed:

sudo apt install traceroute

This command helps identify routing issues.

Testing DNS Resolution

Use nslookup.

nslookup gohackerscloud.com

Or:

dig gohackerscloud.com

Install if required.

sudo apt install dnsutils

These tools verify DNS functionality.

Viewing Open Ports

Display listening services.

ss -tuln

Example output:

22

SSH

80

HTTP

443

HTTPS

The ss command replaces the older netstat utility.

Using netstat

Some enterprise systems still use:

netstat -tuln

Install if required.

sudo apt install net-tools

Testing HTTP Connectivity

Retrieve a webpage.

curl https://www.gohackerscloud.com

View only headers.

curl -I https://www.gohackerscloud.com

curl is widely used for testing APIs and web services.

Downloading Files

Use wget.

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

This downloads files directly from the command line.

Checking Active Connections

Display active network connections.

ss -tunap

This command helps identify active clients and services.

Viewing Network Statistics

Display interface statistics.

ip -s link

Useful information includes:

Packets Sent
Packets Received
Errors
Dropped Packets

Restarting Network Services

Ubuntu (NetworkManager):

sudo systemctl restart NetworkManager

Ubuntu Server (systemd-networkd):

sudo systemctl restart systemd-networkd

Restart networking after configuration changes if required.

Linux Networking in Cloud Computing

Cloud Engineers regularly configure networking on Linux virtual machines.

Examples:

AWS EC2

Private IP
Elastic IP
Security Groups
Route Tables

Azure Virtual Machine

Virtual Network
Network Security Groups

Google Compute Engine

VPC Network
Firewall Rules

Linux networking knowledge is essential for cloud administration.

Linux Networking in Kubernetes

Every Kubernetes node relies on Linux networking.

Examples include:

Pod Communication
Cluster Networking
CNI Plugins
DNS Resolution
Service Discovery

Networking issues are among the most common Kubernetes troubleshooting scenarios.

Linux Networking in Cybersecurity

Security professionals investigate:

Open ports
Unauthorized connections
DNS anomalies
Packet loss
Suspicious outbound traffic
Remote access sessions

Many security investigations begin with Linux networking commands.

Common Networking Commands

Display interfaces:

ip link

Display IP addresses:

ip addr

Display routing table:

ip route

Display hostname:

hostnamectl

Ping host:

ping google.com

DNS lookup:

dig gohackerscloud.com

Display listening ports:

ss -tuln

Download webpage:

curl https://www.gohackerscloud.com

Download file:

wget URL

Real-World Example

A Cloud Engineer deploys an application to an Ubuntu server.

After deployment, users cannot access the website.

The engineer investigates using the following workflow:

Check IP Address

↓

ip addr

↓

Verify Default Gateway

↓

ip route

↓

Test DNS

↓

dig gohackerscloud.com

↓

Check Web Server

↓

systemctl status nginx

↓

Verify Port 443

↓

ss -tuln

↓

Website Restored

This structured troubleshooting process is commonly used in enterprise environments.

Best Practices

As a Linux administrator:

Use ip instead of deprecated networking tools where possible.
Assign meaningful hostnames.
Verify DNS configuration after deployment.
Monitor open ports regularly.
Remove unused network services.
Document IP addressing schemes.
Restrict unnecessary inbound ports using firewalls.
Test connectivity after every network change.

Good networking practices improve reliability, security, and maintainability.

Key Takeaways

After completing this lesson, you should understand:

Linux network interfaces.
IP address configuration.
Routing and default gateways.
DNS configuration.
Network troubleshooting commands.
Open ports and active connections.
Linux networking in cloud and enterprise environments.

Summary

Linux Networking is a core skill for every IT professional.

Whether you’re deploying cloud infrastructure, managing enterprise servers, troubleshooting applications, or investigating cybersecurity incidents, you’ll rely on Linux networking commands every day.

By mastering interfaces, IP addressing, DNS, routing, and troubleshooting tools, you’ll be well prepared to administer Linux systems in AWS, Azure, Google Cloud, Kubernetes, and enterprise data centers.

Next Lesson

➡️ Lesson 10 — Linux Storage & Disk Management

In the next lesson, you’ll learn how Linux manages disks, partitions, file systems, mounting, storage devices, and logical volume management (LVM), and discover how enterprise Linux servers handle persistent storage.