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IP Configuration — Configuring Network Interfaces in Linux

IP Configuration is the process of assigning and managing IP addresses, subnet masks, gateways, DNS servers, and network interfaces. Every Linux server, cloud virtual machine, Kubernetes node, and container requires proper IP configuration to communicate with other systems. Understanding IP configuration is a fundamental skill for Linux administrators, DevOps engineers, Cloud Architects, Network Engineers, and Site Reliability Engineers (SREs).

Learning Path

Linux Mastery → Module 8: Networking → Lesson 2

Difficulty: Beginner → Intermediate

Reading Time: 70 Minutes

Course Progress

Course: Linux Mastery

Module: Networking

Lesson: 2 of 13

What You'll Learn

After completing this lesson, you'll be able to:

  • Understand network interfaces
  • View IP configurations
  • Configure static IP addresses
  • Understand DHCP
  • Manage network interfaces
  • Configure gateways
  • Verify network connectivity
  • Apply IP configuration in production

Prerequisites

Complete:

  • Module 1 – Linux Fundamentals
  • Module 2 – Linux Command Line Essentials
  • Module 3 – Text Processing
  • Module 4 – File Management
  • Module 5 – Users and Groups
  • Module 6 – Process Management
  • Module 7 – Package Management
  • Module 8 Lesson 1 – TCP/IP Basics

Why Learn IP Configuration?

Imagine:

  • A new cloud server cannot reach the Internet.
  • A Kubernetes node cannot join the cluster.
  • SSH access stops working.
  • Two servers cannot communicate.

In many cases, the root cause is an incorrect IP configuration.

What is IP Configuration?

IP configuration defines how a device communicates on a network.

Typical configuration includes:

  • IP Address
  • Subnet Mask (or Prefix Length)
  • Default Gateway
  • DNS Server
  • Network Interface

Without proper configuration, network communication is not possible.

Network Configuration Components

Network Interface
        │
        ▼
IP Address
        │
        ▼
Subnet Mask
        │
        ▼
Default Gateway
        │
        ▼
DNS Server

Each component plays a specific role in network communication.

Network Interfaces

A network interface connects the operating system to a network.

Common interface names:

eth0

ens33

ens160

enp0s3

wlan0

Modern Linux systems use predictable network interface names such as ens160 or enp0s3.

View Network Interfaces

Display all interfaces.

ip link

Example:

lo

ens160

Loopback Interface

Linux includes a special interface:

lo

Loopback address:

127.0.0.1

Purpose:

  • Local communication
  • Testing
  • Internal services

View IP Addresses

Display configured IP addresses.

ip addr

Example:

192.168.1.100/24

Show a specific interface.

ip addr show ens160

Understanding CIDR Notation

Example:

192.168.1.100/24

Meaning:

  • IP Address:
192.168.1.100
  • Prefix Length:
24

Equivalent subnet mask:

255.255.255.0

Static IP Address

A static IP address remains the same until changed manually.

Example:

192.168.1.100

Advantages:

  • Predictable
  • Ideal for servers
  • Required for many production workloads

Dynamic IP Address (DHCP)

DHCP stands for:

Dynamic Host Configuration Protocol

A DHCP server automatically assigns:

  • IP Address
  • Gateway
  • DNS Server
  • Lease Time

Commonly used for:

  • Laptops
  • Desktops
  • Home networks
  • Cloud instances (during initial provisioning)

Assign a Temporary IP Address

Assign an IP address to an interface.

sudo ip addr add 192.168.1.100/24 dev ens160

Verify:

ip addr show ens160

This change is temporary and will be lost after a reboot or interface reset.

Remove an IP Address

sudo ip addr del 192.168.1.100/24 dev ens160

Enable a Network Interface

sudo ip link set ens160 up

Disable a Network Interface

sudo ip link set ens160 down

Use with caution on remote systems, as it may disconnect your session.

View Routing Information

Display the routing table.

ip route

Example:

default via 192.168.1.1

Default Gateway

The default gateway is the router used to reach networks outside the local subnet.

Example:

192.168.1.1

View the default gateway.

ip route

Add a Temporary Default Gateway

sudo ip route add default via 192.168.1.1

Delete the default gateway.

sudo ip route del default

Test Connectivity

Ping the gateway.

ping 192.168.1.1

Ping an external IP.

ping 8.8.8.8

Ping a domain.

ping google.com

Persistent Configuration

Temporary changes made with the ip command are not preserved after a reboot.

Persistent configuration depends on the Linux distribution.

Common tools include:

Distribution Common Configuration Method
Ubuntu Server Netplan
RHEL / Rocky / AlmaLinux NetworkManager (nmcli) or network configuration files
Fedora NetworkManager

Common Commands

View interfaces.

ip link

View IP addresses.

ip addr

View routing table.

ip route

Bring interface up.

sudo ip link set ens160 up

Bring interface down.

sudo ip link set ens160 down

Real Production Examples

Display server IP.

ip addr

Verify default route.

ip route

Test gateway.

ping 192.168.1.1

Enable interface.

sudo ip link set ens160 up

Production Perspective

IP configuration is required for:

  • Cloud virtual machines
  • Kubernetes nodes
  • Docker hosts
  • Database servers
  • Web servers
  • VPN gateways
  • Firewalls
  • Enterprise networks

Incorrect IP configuration is one of the most common causes of network connectivity issues.

Hands-on Lab

Task 1

List network interfaces.

ip link

Task 2

Display IP addresses.

ip addr

Task 3

View the routing table.

ip route

Task 4

Identify the default gateway.

ip route

Task 5

Test gateway connectivity.

ping <gateway-ip>

Replace <gateway-ip> with the gateway shown in your routing table.

Task 6

Display the loopback interface.

ip addr show lo

Task 7

Bring a non-production interface down and back up (if available).

sudo ip link set <interface> down

sudo ip link set <interface> up

Do not perform this on a remote production server or on the interface you're currently using.

Task 8

Display the IP configuration for a specific interface.

ip addr show <interface>

Replace <interface> with your network interface name (for example, ens160).

Command Deep Dive

Command Purpose Production Example
ip addr View IP addresses Verify server configuration
ip link View network interfaces Interface management
ip route Display routing table Routing verification
ip addr add Assign temporary IP Testing
ip addr del Remove temporary IP Cleanup
ip link set up Enable interface Restore connectivity
ip link set down Disable interface Maintenance

Production Troubleshooting Scenario

Scenario

A newly provisioned cloud virtual machine cannot access the Internet.

Investigation:

Check the IP address.

ip addr

Verify the routing table.

ip route

Check connectivity to the gateway.

ping <gateway-ip>

The default route is missing.

Temporarily add the gateway.

sudo ip route add default via <gateway-ip>

Verify Internet access.

ping 8.8.8.8

The server can now reach external networks. A persistent configuration is then applied using the distribution's network management tools.

Best Practices

  • Use static IP addresses for production servers.
  • Use DHCP where automatic configuration is appropriate.
  • Verify the default gateway after configuration changes.
  • Use the ip command instead of the deprecated ifconfig.
  • Test connectivity after making network changes.
  • Apply persistent configuration using the distribution's supported network management tools.

Common Mistakes

❌ Forgetting that ip command changes are temporary.

✅ Remember to that ip command changes are temporary.

❌ Bringing down the active network interface on a remote server.

✅ Avoid this mistake: bringing down the active network interface on a remote server.

❌ Configuring an incorrect subnet or gateway.

✅ Avoid this mistake: configuring an incorrect subnet or gateway.

❌ Forgetting to verify routing after assigning an IP address.

✅ Remember to to verify routing after assigning an IP address.

Interview Questions

Beginner

  1. What is an IP address?
  2. What is the difference between a static IP address and DHCP?
  3. Which command displays IP addresses?
  4. What is the purpose of the loopback interface?

Intermediate

  1. What is CIDR notation?
  2. How do you temporarily assign an IP address?
  3. How do you view the routing table?
  4. Why is the default gateway important?

Architect Level

  1. How would you configure networking for production Linux servers?
  2. How would you troubleshoot a server that cannot reach the Internet?
  3. Why are static IP addresses commonly used for infrastructure services?

Summary

In this lesson, you learned:

  • IP configuration
  • Network interfaces
  • Static and dynamic addressing
  • DHCP
  • Routing
  • Default gateways
  • Temporary network configuration
  • Production networking best practices

Proper IP configuration is the foundation of Linux networking. Every server, container, and cloud instance depends on correctly configured network interfaces, IP addresses, gateways, and routing information to communicate reliably.

Key Takeaways

  • Every network interface requires proper IP configuration.
  • Static IP addresses are preferred for production servers.
  • DHCP automatically assigns network settings.
  • The ip command is the standard tool for Linux network configuration.
  • The default gateway enables communication outside the local network.
  • Changes made with the ip command are temporary unless made persistent.

What's Next?

DNS (Domain Name System) — Translating Domain Names into IP Addresses

You'll explore:

  • How DNS works
  • DNS records
  • Name resolution
  • DNS configuration
  • DNS troubleshooting
  • Common DNS tools
  • Production DNS best practices

Understanding DNS is essential because nearly every network application depends on reliable name resolution.