Networking in Linux - Network Configuration Files

Published on December 7, 2025 by Team SKY | Tags: DevOps, System Administration, Networking

Linux networking configuration involves multiple approaches and configuration files across different distributions. Understanding these files and systems is crucial for managing network interfaces, DNS resolution, hostnames, and network services. This comprehensive guide covers traditional configuration files, modern network managers, and distribution-specific approaches.

Network Configuration Systems Comparison

Configuration System Distributions Primary Files Management Tools Use Case
Traditional Files Debian, older systems /etc/network/interfaces
/etc/resolv.conf		 ifup, ifdown, ip Simple static configurations
NetworkManager Most modern distros Keyfile, ifcfg-rh nmcli, nmtui, GUI Desktop, dynamic networks
systemd-networkd Recent systemd distros /etc/systemd/network/ networkctl, systemctl Server, minimal systems
netplan Ubuntu 18.04+ /etc/netplan/ netplan apply Cloud, Ubuntu servers
Quick Reference:
• Check current system: ps aux | grep -E '(NetworkManager|systemd-networkd)'
• View interfaces: ip addr show or ifconfig
• Test connectivity: ping -c 3 8.8.8.8 and ping -c 3 google.com
• Check DNS: nslookup google.com or dig google.com
• Always backup config files before making changes
• Test network changes in non-production environments first

Network Configuration Workflow

Complete Network Configuration Process

Identify Interface
→
Choose Method
→
Edit Config
→
Apply Changes
→
Test Connectivity
→
Verify DNS

Essential Network Configuration Files

Configuration File Purpose Distributions Syntax Restart Command
/etc/hostname System hostname All Linux Plain text hostnamectl set-hostname
/etc/hosts Local hostname resolution All Linux IP hostname aliases Immediate
/etc/resolv.conf DNS servers All Linux nameserver, search Immediate
/etc/nsswitch.conf Name service switch All Linux Service order Immediate
/etc/network/interfaces Network interfaces (Debian) Debian/Ubuntu iface, auto, allow-* systemctl restart networking
/etc/sysconfig/network-scripts/ Network interfaces (Red Hat) RHEL/CentOS KEY=VALUE pairs systemctl restart network

Traditional Network Configuration

🔧
Debian/Ubuntu Interfaces

Configure network interfaces using /etc/network/interfaces.

/etc/network/interfaces

Common Configurations:

# Static IP configuration
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 8.8.8.8 8.8.4.4

# DHCP configuration
auto eth0
iface eth0 inet dhcp

# Bridge configuration
auto br0
iface br0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    bridge_ports eth0
🔴
Red Hat/CentOS Interfaces

Configure network interfaces using ifcfg files.

/etc/sysconfig/network-scripts/ifcfg-*

Common Configurations:

# Static IP - /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
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
TYPE=Ethernet

# DHCP - /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
TYPE=Ethernet

# Bridge - /etc/sysconfig/network-scripts/ifcfg-br0
DEVICE=br0
TYPE=Bridge
BOOTPROTO=static
IPADDR=192.168.1.100
NETMASK=255.255.255.0
ONBOOT=yes
🌐
DNS & Host Configuration

Configure hostname resolution and DNS settings.

/etc/hosts, /etc/resolv.conf, /etc/hostname

Configuration Files:

# /etc/hostname
server1.example.com

# /etc/hosts
127.0.0.1   localhost localhost.localdomain
192.168.1.100 server1.example.com server1
192.168.1.101 server2.example.com server2

# /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
search example.com local

Modern Network Managers

Network Manager Configuration Files Management Tools Best For Example Distributions
NetworkManager /etc/NetworkManager/
~/.config/NetworkManager/		 nmcli, nmtui, GUI Desktops, laptops Ubuntu, Fedora, RHEL
systemd-networkd /etc/systemd/network/ networkctl, systemctl Servers, minimal systems Ubuntu Server, CoreOS
netplan /etc/netplan/*.yaml netplan apply Ubuntu servers, cloud Ubuntu 18.04+
Traditional /etc/network/interfaces
/etc/sysconfig/network-scripts/		 ifup, ifdown, ip Simple setups Debian, CentOS 7

NetworkManager Configuration

📡
nmcli Command Line

Manage NetworkManager from command line.

nmcli [options] command

Common Commands:

  • nmcli connection show - List connections
  • nmcli device status - Show device status
  • nmcli connection up "connection-name" - Activate connection
  • nmcli connection down "connection-name" - Deactivate connection

Configuration Examples:

# Add static IP connection
nmcli connection add type ethernet con-name "static-eth0" \
  ifname eth0 ip4 192.168.1.100/24 gw4 192.168.1.1

# Modify existing connection
nmcli connection modify "static-eth0" ipv4.dns "8.8.8.8,8.8.4.4"

# Add WiFi connection
nmcli device wifi connect "SSID" password "password"
📁
NetworkManager Files

Configuration files for NetworkManager.

/etc/NetworkManager/

Key Files:

  • NetworkManager.conf - Main configuration
  • system-connections/ - Connection profiles
  • conf.d/ - Additional configuration

Connection File Example:

# /etc/NetworkManager/system-connections/static-eth0.nmconnection
[connection]
id=static-eth0
type=ethernet
interface-name=eth0

[ipv4]
method=manual
addresses=192.168.1.100/24
gateway=192.168.1.1
dns=8.8.8.8;8.8.4.4;

[ipv6]
method=auto
🖥️
nmtui Text UI

Text-based user interface for NetworkManager.

nmtui

Features:

  • Interactive text interface
  • No X server required
  • Easy connection management
  • Systemd service integration

Usage:

# Start nmtui
sudo nmtui

# Available options:
# - Edit a connection
# - Activate a connection  
# - Set system hostname
# - Quit

systemd-networkd Configuration

⚙️
Network Configuration

Configure networks with systemd-networkd.

/etc/systemd/network/*.network

Example Configurations:

# /etc/systemd/network/10-eth0.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
Domains=example.com

# DHCP configuration
[Match]
Name=eth0

[Network]
DHCP=yes
🔗
Link Configuration

Configure network device properties.

/etc/systemd/network/*.link

Link File Examples:

# /etc/systemd/network/10-eth0.link
[Match]
MACAddress=00:11:22:33:44:55

[Link]
Name=eth0
MTUBytes=1500
WakeOnLan=magic

# Rename interface by MAC
[Match]
MACAddress=aa:bb:cc:dd:ee:ff

[Link]
Name=lan0
🌉
Bridge & VLAN

Configure advanced network features.

.netdev files

Advanced Configurations:

# Bridge - /etc/systemd/network/20-br0.netdev
[NetDev]
Name=br0
Kind=bridge

# VLAN - /etc/systemd/network/30-vlan100.netdev
[NetDev]
Name=vlan100
Kind=vlan

[VLAN]
Id=100

# Bridge network configuration
[Match]
Name=br0

[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1

Netplan Configuration (Ubuntu)

⚡
YAML Configuration

Configure networks using Netplan YAML files.

/etc/netplan/*.yaml

Example Configurations:

# /etc/netplan/01-netcfg.yaml
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - 192.168.1.100/24
      gateway4: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
      routes:
        - to: 10.0.0.0/8
          via: 192.168.1.254

# DHCP configuration
network:
  version: 2
  renderer: NetworkManager
  ethernets:
    eth0:
      dhcp4: true
      dhcp6: false
🔧
Netplan Commands

Manage and apply Netplan configurations.

netplan [command]

Common Commands:

  • netplan generate - Generate configuration
  • netplan apply - Apply configuration
  • netplan try - Apply with rollback
  • netplan info - Show debug information

Usage:

# Apply network configuration
sudo netplan apply

# Test configuration with rollback
sudo netplan try
# Press ENTER to accept, Ctrl+C to revert

# Generate configuration files
sudo netplan generate
🌉
Advanced Netplan

Configure bridges, bonds, and VLANs with Netplan.

Bridges, bonds, VLANs in YAML

Advanced Configurations:

# Bridge configuration
network:
  version: 2
  renderer: networkd
  bridges:
    br0:
      interfaces: [eth0]
      addresses: [192.168.1.100/24]
      gateway4: 192.168.1.1

# Bond configuration
network:
  version: 2
  bonds:
    bond0:
      interfaces: [eth0, eth1]
      parameters:
        mode: 802.3ad
        lacp-rate: fast

# VLAN configuration
network:
  version: 2
  vlans:
    vlan100:
      id: 100
      link: eth0
      addresses: [192.168.100.100/24]

Practical Network Configuration Examples

Real-World Network Configuration Scenarios

# 1. Basic Static IP Configuration
# Debian/Ubuntu - /etc/network/interfaces
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 8.8.8.8 8.8.4.4
    dns-search example.com

# Red Hat/CentOS - /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
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
DOMAIN=example.com

# 2. NetworkManager - Static IP
sudo nmcli connection add type ethernet con-name "static-eth0" \
  ifname eth0 ip4 192.168.1.100/24 gw4 192.168.1.1
sudo nmcli connection modify "static-eth0" ipv4.dns "8.8.8.8,8.8.4.4"
sudo nmcli connection modify "static-eth0" ipv4.dns-search "example.com"
sudo nmcli connection up "static-eth0"

# 3. systemd-networkd - Static IP
# /etc/systemd/network/10-eth0.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
Domains=example.com

# Enable and start
sudo systemctl enable systemd-networkd
sudo systemctl start systemd-networkd

# 4. Netplan - Static IP (Ubuntu)
# /etc/netplan/01-netcfg.yaml
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses: [192.168.1.100/24]
      gateway4: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
        search: [example.com]

sudo netplan apply

# 5. Multiple IP Addresses on Single Interface
# Debian/Ubuntu - /etc/network/interfaces
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1

auto eth0:0
iface eth0:0 inet static
    address 192.168.1.101
    netmask 255.255.255.0

# NetworkManager
sudo nmcli connection modify "static-eth0" +ipv4.addresses "192.168.1.101/24"

# systemd-networkd
[Match]
Name=eth0

[Network]
Address=192.168.1.100/24
Address=192.168.1.101/24
Gateway=192.168.1.1

# 6. Bridge Configuration Examples
# Debian/Ubuntu Bridge
auto br0
iface br0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    bridge_ports eth0
    bridge_stp off
    bridge_fd 0
    bridge_maxwait 0

# NetworkManager Bridge
sudo nmcli connection add type bridge con-name br0 ifname br0
sudo nmcli connection modify br0 ipv4.addresses 192.168.1.100/24
sudo nmcli connection modify br0 ipv4.gateway 192.168.1.1
sudo nmcli connection modify br0 ipv4.method manual
sudo nmcli connection add type ethernet con-name br0-slave ifname eth0 master br0

# 7. Bonding Configuration
# NetworkManager Bond
sudo nmcli connection add type bond con-name bond0 ifname bond0 \
  bond.options "mode=active-backup,miimon=100"
sudo nmcli connection add type ethernet con-name bond0-slave1 ifname eth0 master bond0
sudo nmcli connection add type ethernet con-name bond0-slave2 ifname eth1 master bond0
sudo nmcli connection modify bond0 ipv4.addresses 192.168.1.100/24
sudo nmcli connection modify bond0 ipv4.gateway 192.168.1.1
sudo nmcli connection modify bond0 ipv4.method manual

# 8. VLAN Configuration
# NetworkManager VLAN
sudo nmcli connection add type vlan con-name vlan100 ifname vlan100 \
  dev eth0 id 100
sudo nmcli connection modify vlan100 ipv4.addresses 192.168.100.100/24
sudo nmcli connection modify vlan100 ipv4.method manual

# 9. Wireless Configuration
# NetworkManager WiFi
sudo nmcli device wifi list
sudo nmcli device wifi connect "MySSID" password "mypassword"

# Persistent WiFi configuration
sudo nmcli connection add type wifi con-name "MyWiFi" \
  ifname wlan0 ssid "MySSID"
sudo nmcli connection modify "MyWiFi" wifi-sec.key-mgmt wpa-psk
sudo nmcli connection modify "MyWiFi" wifi-sec.psk "mypassword"

# 10. DNS Configuration Scenarios
# Static DNS in /etc/resolv.conf (not recommended - use below methods)
nameserver 8.8.8.8
nameserver 8.8.4.4
search example.com local

# NetworkManager DNS
sudo nmcli connection modify "static-eth0" ipv4.dns "8.8.8.8,8.8.4.4"
sudo nmcli connection modify "static-eth0" ipv4.dns-search "example.com,local"

# systemd-resolved configuration
# /etc/systemd/resolved.conf
[Resolve]
DNS=8.8.8.8 8.8.4.4
Domains=example.com
FallbackDNS=1.1.1.1 1.0.0.1

# 11. Hostname Configuration
# Temporary hostname
sudo hostname new-hostname

# Permanent hostname
echo "new-hostname" | sudo tee /etc/hostname
sudo hostnamectl set-hostname new-hostname

# Update /etc/hosts
127.0.0.1   localhost localhost.localdomain
192.168.1.100 new-hostname.example.com new-hostname

# 12. Routing Configuration
# Add static route
sudo ip route add 10.0.0.0/8 via 192.168.1.254 dev eth0

# Persistent routes - Debian/Ubuntu
# /etc/network/interfaces
up ip route add 10.0.0.0/8 via 192.168.1.254 dev eth0

# Persistent routes - Red Hat/CentOS
# /etc/sysconfig/network-scripts/route-eth0
10.0.0.0/8 via 192.168.1.254 dev eth0

# 13. Network Troubleshooting Commands
# Check interface status
ip addr show
ip link show

# Check routing table
ip route show
route -n

# Check DNS resolution
nslookup google.com
dig google.com

# Check network connectivity
ping -c 4 8.8.8.8
ping -c 4 google.com

# Check listening ports
ss -tuln
netstat -tuln

# Check network statistics
ip -s link
netstat -i

# 14. Network Service Management
# Traditional Debian/Ubuntu
sudo systemctl restart networking

# Traditional Red Hat/CentOS
sudo systemctl restart network

# NetworkManager
sudo systemctl restart NetworkManager

# systemd-networkd
sudo systemctl restart systemd-networkd

# 15. Security Hardening
# Disable unused network services
sudo systemctl disable bluetooth
sudo systemctl stop bluetooth

# Configure firewall
sudo ufw enable
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw allow ssh

# Or use iptables directly
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
sudo iptables -A INPUT -j DROP

Common Use Cases

Server Environments

  • Static IP Configuration: Reliable network configuration for servers
  • Multiple Interfaces: Separate management and data networks
  • Bonding: Network redundancy and increased bandwidth
  • VLANs: Network segmentation for security

Cloud & Virtualization

  • Bridged Networking: Virtual machines with direct network access
  • NAT Configuration: Isolated virtual networks
  • Cloud-init: Automated network configuration in cloud environments
  • Container Networking: Network namespaces and virtual interfaces

Development & Testing

  • Multiple IPs: Testing different network configurations
  • Network Isolation: Creating test environments
  • DNS Configuration: Local development domains
  • Proxy Settings: Development behind corporate firewalls

Advanced Network Configuration

🛡️

Network Security

Secure network configuration and hardening.

Firewalls, VPNs, secure protocols

Security Measures:

  • Configure firewalls (iptables, ufw, firewalld)
  • Use SSH key authentication
  • Disable unused network services
  • Implement VPN for remote access

Example:

# Basic ufw configuration
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw allow ssh
sudo ufw allow 80/tcp
sudo ufw enable
📊

Network Monitoring

Monitor network performance and troubleshoot issues.

Monitoring tools and commands

Monitoring Tools:

  • iftop - Bandwidth monitoring
  • nethogs - Process bandwidth usage
  • tcpdump - Packet capture
  • netstat - Network statistics

Usage:

# Monitor bandwidth by interface
sudo iftop -i eth0

# Monitor bandwidth by process
sudo nethogs eth0

# Capture packets
sudo tcpdump -i eth0 -w capture.pcap
🔧

Performance Tuning

Optimize network performance for specific use cases.

Kernel parameters and interface settings

Tuning Parameters:

  • TCP buffer sizes
  • Interface MTU settings
  • Interrupt coalescing
  • Queue disciplines

Examples:

# Increase TCP buffer sizes
echo 'net.core.rmem_max = 16777216' >> /etc/sysctl.conf
echo 'net.core.wmem_max = 16777216' >> /etc/sysctl.conf
sysctl -p
Important Considerations:
• Always backup network configuration files before making changes
• Test network changes in non-production environments first
• Be cautious when changing network configurations remotely - you may lose connectivity
• Understand the difference between temporary and permanent network changes
• Keep network configuration files in version control for reproducibility
• Document network configurations for troubleshooting and recovery
• Consider using configuration management tools for complex environments
• Regularly review and update network security configurations
Pro Tips:
• Use ip addr show instead of deprecated ifconfig
• Use ss instead of netstat for better performance
• Test both IP and hostname connectivity to diagnose DNS issues
• Use mtr instead of traceroute for continuous route monitoring
• Configure network bonding for redundancy in server environments
• Use VLANs to segment network traffic for security
• Implement network monitoring and alerting for production systems
• Use configuration management (Ansible, Puppet) for consistent network configurations

Key Takeaways

Mastering Linux network configuration is essential for system administrators, DevOps engineers, and network professionals. Understanding the different configuration systems - from traditional files to modern managers like NetworkManager, systemd-networkd, and Netplan - allows you to work effectively across various Linux distributions and environments. Remember that network configuration involves not just IP addresses and DNS, but also routing, security, performance tuning, and troubleshooting. Whether you're managing a single server or an entire data center, these skills ensure reliable, secure, and performant network connectivity.

Next Step: Explore advanced networking topics like network namespaces, software-defined networking (SDN), container networking, and network automation with tools like Ansible and Terraform.