Skip to main content

Chapter 7.1 - Network Interfaces

Learning Objectives​

By the end of this chapter, you will be able to:

  • Understand Linux network interfaces
  • Configure interfaces with ip and ifconfig
  • Manage IP addresses
  • Understand network configuration files
  • Enable/disable interfaces

Network Interfaces​

Types of Interfaces​

Types:

  • eth0, eth1: Physical Ethernet interfaces
  • wlan0: WiFi interface
  • lo: Loopback (127.0.0.1)
  • virbr0, veth: Virtual interfaces (VM, containers)

Basic Commands​

ip - Modern Command​

# View all interfaces
ip addr show
ip a
ip address

# View specific interface
ip addr show eth0

# View only active interfaces
ip link show up

# Statistics
ip -s link show

ifconfig - Classic Command​

# View all interfaces
ifconfig -a

# View specific interface
ifconfig eth0

# Install if necessary (net-tools)
sudo apt install net-tools  # Ubuntu/Debian

IP Configuration​

Add an IP Address​

# With ip
sudo ip addr add 192.168.1.100/24 dev eth0

# With ifconfig
sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0

# Verify
ip addr show eth0

Remove an IP Address​

# With ip
sudo ip addr del 192.168.1.100/24 dev eth0

# With ifconfig
sudo ifconfig eth0 0.0.0.0

Multiple IP Addresses​

# Add multiple IPs on an interface
sudo ip addr add 192.168.1.100/24 dev eth0
sudo ip addr add 192.168.1.101/24 dev eth0

# View all IPs
ip addr show eth0

Enable/Disable Interfaces​

With ip​

# Enable
sudo ip link set eth0 up

# Disable
sudo ip link set eth0 down

# View status
ip link show eth0

With ifconfig​

# Enable
sudo ifconfig eth0 up

# Disable
sudo ifconfig eth0 down

Permanent Configuration​

Ubuntu/Debian (Netplan)​

# /etc/netplan/01-netcfg.yaml
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: true
      # Or static:
      # addresses:
      #   - 192.168.1.100/24
      # gateway4: 192.168.1.1
      # nameservers:
      #   addresses:
      #     - 8.8.8.8
      #     - 8.8.4.4

Apply:

sudo netplan apply
sudo netplan try  # Test with rollback

Red Hat/CentOS (NetworkManager)​

# File: /etc/sysconfig/network-scripts/ifcfg-eth0
TYPE=Ethernet
BOOTPROTO=static
NAME=eth0
DEVICE=eth0
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:

sudo systemctl restart NetworkManager

Manual Configuration (systemd-networkd)​

# /etc/systemd/network/20-wired.network
[Match]
Name=eth0

[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1
DNS=8.8.8.8
DNS=8.8.4.4

Interface Information​

Full Details​

# With ip
ip -d link show eth0  # Details
ip -s -s link show eth0  # Detailed statistics

# With ethtool (install if necessary)
sudo apt install ethtool
ethtool eth0  # Hardware information
ethtool -S eth0  # Statistics

MTU​

# View MTU
ip link show eth0 | grep mtu

# Change MTU
sudo ip link set eth0 mtu 1500

Practical Examples​

Static Configuration​

#!/bin/bash
# Network configuration script

INTERFACE="eth0"
IP="192.168.1.100"
NETMASK="255.255.255.0"
GATEWAY="192.168.1.1"

# Configure IP
sudo ip addr add $IP/24 dev $INTERFACE

# Enable interface
sudo ip link set $INTERFACE up

# Add default route
sudo ip route add default via $GATEWAY

Verification​

#!/bin/bash
# Verify network configuration

echo "=== Interfaces ==="
ip addr show

echo "=== Routes ==="
ip route show

echo "=== Connections ==="
ss -tuln

Summary​

In this chapter, you learned:

Interfaces: eth0, wlan0, lo, virtual interfaces
Commands: ip (modern), ifconfig (classic)
Configuration: IP, netmask, enable/disable
Permanent: Netplan (Ubuntu), NetworkManager (Red Hat), systemd-networkd
Information: ip -d, ethtool for details
Practical: Configuration and verification scripts

Next Steps​

Chapter 7.2: Routing and Routing Tables
Chapter 7.3: DNS and Name Resolution

Chapter created on: December 2024