systemd-networkd Linux: Complete Network Configuration Manager Guide

systemd-networkd is a powerful system daemon that manages network configurations on Linux systems. As part of the systemd ecosystem, it provides a declarative approach to network configuration, making it easier to manage complex network setups with consistent and predictable behavior.

What is systemd-networkd?

systemd-networkd is a system service that manages network configurations through configuration files. Unlike traditional network management tools, it integrates seamlessly with systemd, providing better integration with other system services and improved boot-time network setup.

Key Features

• Declarative Configuration: Define network settings in simple configuration files
• Dynamic Reconfiguration: Apply changes without system restart
• DHCP Support: Built-in DHCP client and server capabilities
• Link Aggregation: Support for bonding and bridging
• VLAN Support: Easy VLAN configuration and management
• IPv6 Ready: Full IPv6 support including auto-configuration

Installation and Setup

Most modern Linux distributions include systemd-networkd by default. Here’s how to enable and start the service:

# Enable systemd-networkd
sudo systemctl enable systemd-networkd

# Start the service
sudo systemctl start systemd-networkd

# Check service status
sudo systemctl status systemd-networkd

Expected output:

● systemd-networkd.service - Network Service
     Loaded: loaded (/lib/systemd/system/systemd-networkd.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2025-08-26 02:41:15 IST; 2min 34s ago
       Docs: man:systemd-networkd.service(8)
   Main PID: 1234 (systemd-network)
     Status: "Processing requests..."
      Tasks: 1 (limit: 4915)
     Memory: 2.1M
        CPU: 15ms
     CGroup: /system.slice/systemd-networkd.service
             └─1234 /lib/systemd/systemd-networkd

Configuration File Structure

systemd-networkd uses three types of configuration files:

• .netdev files: Define virtual network devices
• .network files: Configure network interfaces
• .link files: Configure physical link properties

Configuration Directories

Configuration files are stored in these directories (in order of precedence):

/etc/systemd/network/          # System administrator files
/run/systemd/network/          # Runtime files
/lib/systemd/network/          # Distribution provided files

Basic Network Configuration

Static IP Configuration

Create a network configuration file for static IP assignment:

# Create configuration file
sudo nano /etc/systemd/network/20-wired.network

Add the following configuration:

[Match]
Name=eth0

[Network]
DHCP=no
Address=192.168.1.100/24
Gateway=192.168.1.1
DNS=8.8.8.8
DNS=8.8.4.4

DHCP Configuration

For dynamic IP assignment using DHCP:

[Match]
Name=eth0

[Network]
DHCP=ipv4

[DHCP]
UseDNS=yes
UseRoutes=yes

Dual Stack (IPv4 + IPv6) Configuration

[Match]
Name=eth0

[Network]
DHCP=yes
IPv6AcceptRA=yes

[DHCP]
UseDNS=yes
UseRoutes=yes

Advanced Configuration Examples

VLAN Configuration

First, create a VLAN netdev file:

# /etc/systemd/network/vlan10.netdev
[NetDev]
Name=vlan10
Kind=vlan

[VLAN]
Id=10

Then configure the VLAN network:

# /etc/systemd/network/vlan10.network
[Match]
Name=vlan10

[Network]
DHCP=no
Address=192.168.10.100/24
Gateway=192.168.10.1

Configure the physical interface to support VLAN:

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

[Network]
VLAN=vlan10

Bridge Configuration

Create a bridge netdev:

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

Configure the bridge network:

# /etc/systemd/network/br0.network
[Match]
Name=br0

[Network]
DHCP=yes

Bind physical interfaces to the bridge:

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

[Network]
Bridge=br0

Bond Configuration

Create a bond netdev:

# /etc/systemd/network/bond0.netdev
[NetDev]
Name=bond0
Kind=bond

[Bond]
Mode=active-backup
MIIMonitorSec=1s

Configure bond network:

# /etc/systemd/network/bond0.network
[Match]
Name=bond0

[Network]
DHCP=yes

Bind interfaces to the bond:

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

[Network]
Bond=bond0

# /etc/systemd/network/21-eth1.network
[Match]
Name=eth1

[Network]
Bond=bond0

Managing systemd-networkd

Applying Configuration Changes

After creating or modifying configuration files, reload the service:

# Reload configuration
sudo systemctl reload systemd-networkd

# Or restart the service
sudo systemctl restart systemd-networkd

Viewing Network Status

Use networkctl command to view network status:

# List all network interfaces
networkctl list

Sample output:

IDX LINK   TYPE     OPERATIONAL SETUP     
  1 lo     loopback carrier     unmanaged 
  2 eth0   ether    routable    configured
  3 wlan0  wlan     off         unmanaged

Get detailed status of a specific interface:

networkctl status eth0

Sample output:

● 2: eth0                                                        
                     Link File: /lib/systemd/network/99-default.link
                  Network File: /etc/systemd/network/20-wired.network
                          Type: ether
                         State: routable (configured)
                  Online state: online                           
                      HW Address: 52:54:00:12:34:56 (QEMU virtual NIC)
                           MTU: 1500
                         QDisc: fq_codel
  IPv4 Address Generation Mode: none                           
  IPv6 Address Generation Mode: eui64
          Number of Addresses: 2                               
                       Address: 192.168.1.100/24
                                fe80::5054:ff:fe12:3456/64
                       Gateway: 192.168.1.1
                           DNS: 8.8.8.8
                                8.8.4.4

Troubleshooting Common Issues

Configuration Validation

Check configuration file syntax:

# Validate network configuration
sudo systemd-analyze verify /etc/systemd/network/*.network

Debug Mode

Enable debug logging for detailed troubleshooting:

# Enable debug logging
sudo systemctl edit systemd-networkd

Add the following content:

[Service]
Environment=SYSTEMD_LOG_LEVEL=debug

Restart the service and check logs:

sudo systemctl restart systemd-networkd
sudo journalctl -u systemd-networkd -f

Common Configuration Issues

Interface Not Managed

If an interface shows as “unmanaged”, ensure:

• Configuration file exists with correct [Match] section
• Interface name matches exactly
• No conflicting network managers are running

DHCP Not Working

Check DHCP configuration:

# Verify DHCP settings
networkctl status eth0 | grep -A 5 -B 5 DHCP

DNS Resolution Issues

Ensure systemd-resolved is running and properly configured:

sudo systemctl status systemd-resolved
resolvectl status

Integration with systemd-resolved

systemd-networkd works seamlessly with systemd-resolved for DNS management:

# Enable systemd-resolved
sudo systemctl enable systemd-resolved
sudo systemctl start systemd-resolved

# Check DNS configuration
resolvectl dns

Custom DNS Configuration

Configure DNS settings in network files:

[Network]
DNS=1.1.1.1
DNS=1.0.0.1
Domains=example.com
DNSDefaultRoute=yes

Performance and Best Practices

Configuration Best Practices

• Naming Convention: Use descriptive filenames with proper prefixes (10-, 20-, etc.)
• Match Specificity: Use specific match criteria to avoid conflicts
• Documentation: Add comments to configuration files for clarity
• Testing: Test configurations in non-production environments first

Performance Considerations

# Monitor network performance
networkctl status --all
ss -tuln
ip route show

File Organization Example

/etc/systemd/network/
├── 10-eth0.link          # Physical link properties
├── 20-eth0.network       # Main network configuration
├── 30-br0.netdev         # Bridge device definition
├── 30-br0.network        # Bridge network configuration
├── 40-vlan10.netdev      # VLAN device definition
└── 40-vlan10.network     # VLAN network configuration

Migration from Other Network Managers

From NetworkManager

Disable NetworkManager and enable systemd-networkd:

# Disable NetworkManager
sudo systemctl disable NetworkManager
sudo systemctl stop NetworkManager

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

From ifupdown (Debian/Ubuntu)

Convert /etc/network/interfaces configuration to systemd-networkd format:

# Traditional ifupdown configuration
# auto eth0
# iface eth0 inet static
#   address 192.168.1.100/24
#   gateway 192.168.1.1

# Equivalent systemd-networkd configuration
[Match]
Name=eth0

[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1

Security Considerations

File Permissions

Ensure proper permissions on configuration files:

# Set appropriate permissions
sudo chmod 644 /etc/systemd/network/*.network
sudo chown root:root /etc/systemd/network/*.network

Network Security

Configure secure network settings:

[Network]
# Disable IPv6 router advertisements if not needed
IPv6AcceptRA=no

# Enable privacy extensions for IPv6
IPv6PrivacyExtensions=yes

# Configure link-local addressing
LinkLocalAddressing=ipv4

Conclusion

systemd-networkd provides a robust and flexible approach to network configuration management in Linux systems. Its declarative configuration model, integration with systemd ecosystem, and powerful features make it an excellent choice for both simple and complex network setups.

Key advantages include:

• Consistent configuration across different systems
• Better integration with systemd services
• Powerful features for advanced networking scenarios
• Improved boot-time network initialization
• Extensive logging and debugging capabilities

Whether you’re managing a simple desktop system or complex server infrastructure, systemd-networkd provides the tools and flexibility needed for effective network management. Start with basic configurations and gradually explore advanced features as your networking requirements grow.