Mastering Linux Networking – Essential Commands & Configuration

🔹 Introduction

Mastering Linux Networking: Linux networking is a fundamental aspect of system administration, security, and DevOps operations. Whether you are configuring servers, troubleshooting connectivity problems, or optimizing network performance, having a deep understanding of Linux networking commands is crucial.

In this comprehensive guide, we will explore the core networking commands and configurations that every Linux user, administrator, and network engineer should master.

Topics Covered:

Understanding Linux network interfaces and IP addresses
Configuring network settings and managing connections
Exploring routing tables and adding static routes
Firewall configurations using iptables and firewalld
Diagnosing and troubleshooting network connectivity issues

By the end of this article, you will have a strong grasp of Linux networking fundamentals and advanced configurations. Let’s dive in!

🔢 Checking Network Configuration

Before making any changes to a Linux system’s network settings, it is essential to verify the current configuration.

🔹 Check IP Address and Network Interfaces

The primary command for checking IP addresses and network interfaces is:

ip a

Alternatively, you can use the deprecated but still widely available:

ifconfig

Output Breakdown:

inet displays the assigned IPv4 address.
inet6 lists any assigned IPv6 addresses.
eth0 or wlan0 denotes the network interface name (Ethernet or Wi-Fi).

To check all network interfaces along with their status, use:

ip link show

🔧 Configuring Network Interfaces

🔹 Setting a Static IP Address (Ubuntu/Debian)

For persistent network configurations, edit the Netplan YAML configuration file:

sudo nano /etc/netplan/50-cloud-init.yaml

Example configuration for a static IP setup:

network:
  ethernets:
    eth0:
      dhcp4: no
      addresses: [192.168.1.100/24]
      gateway4: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
  version: 2

Apply the changes with:

sudo netplan apply

🔹 Configuring Network Interfaces (CentOS/RHEL)

Modify the network configuration file for your interface:

sudo nano /etc/sysconfig/network-scripts/ifcfg-eth0

Example static IP configuration:

BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.1.100
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=8.8.8.8
DNS2=8.8.4.4

Restart the network service:

sudo systemctl restart NetworkManager

🚶️ Managing Routing in Linux

🔹 Viewing the Routing Table

To examine the system’s routing table, use:

ip route show

🔹 Adding a Static Route

sudo ip route add 192.168.2.0/24 via 192.168.1.1 dev eth0

🔹 Deleting a Route

sudo ip route del 192.168.2.0/24

🔒 Configuring Linux Firewall (iptables & firewalld)

🔹 Checking Active Firewall Rules

sudo iptables -L -v -n

sudo firewall-cmd --list-all

🔹 Allowing Incoming SSH Traffic (Port 22)

For iptables:

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

For firewalld (CentOS/RHEL):

sudo firewall-cmd --permanent --add-service=ssh
sudo firewall-cmd --reload

🔹 Blocking All Incoming Traffic Except SSH

sudo iptables -P INPUT DROP
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

🔍 Troubleshooting Network Issues in Linux

🔹 Checking Network Connectivity

ping google.com

🔹 Performing a Trace Route to Identify Network Hops

traceroute google.com

🔹 Checking Open Ports

netstat -tulnp

ss -tulnp

🔹 Restarting Network Services

For Ubuntu/Debian:

sudo systemctl restart networking

For CentOS/RHEL:

sudo systemctl restart NetworkManager

📝 Summary

You learned essential Linux networking commands and how to configure network interfaces.
You now understand routing, firewalls, and troubleshooting techniques for managing Linux networks.
Mastering Linux networking is key for system administrators, DevOps engineers, and security professionals.

👉 Next Blog (Feb 15, 2025): Understanding Linux Firewall & Security – iptables & firewalld 🚀

Learn More:

Incident Management

Linux

SQL

💬 Have questions? Drop them in the comments below!