Mastering Netplan and systemd-networkd: Overcome DNS Resolution Nightmares

April 20, 2025

Debugging Netplan and systemd-networkd DNS Resolution Failures

In today’s networked world, reliable DNS resolution is crucial for the seamless operation of applications and services. When using Netplan and systemd-networkd for network configuration on Linux systems, DNS resolution failures can lead to significant disruptions. This guide aims to provide a comprehensive approach to debugging these issues, ensuring that network administrators can quickly identify and resolve DNS-related problems.

Understanding Netplan and systemd-networkd

Netplan is a network configuration abstraction tool for Linux, primarily used in Ubuntu and other distributions. It allows users to define network settings in YAML files, which are then applied by either NetworkManager or systemd-networkd. systemd-networkd is a system service that manages network configurations and connections, providing a robust framework for handling network interfaces.

Common Causes of DNS Resolution Failures

Before diving into debugging steps, it’s essential to understand the common causes of DNS resolution failures:

Incorrect DNS server configuration in Netplan.
Network connectivity issues preventing access to DNS servers.
Firewall rules blocking DNS traffic.
Issues with the DNS server itself.

Configuration Steps for Debugging

Step 1: Verify Netplan Configuration

Start by checking your Netplan configuration file, typically located in /etc/Netplan/. Use the following command to list the files:

ls /etc/Netplan/

Open the relevant YAML file with a text editor:

sudo nano /etc/Netplan/01-netcfg.yaml

Ensure that the DNS settings are correctly specified under the appropriate network interface:

network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true
      nameservers:
        addresses:
          - 8.8.8.8
          - 8.8.4.4

Step 2: Apply Configuration Changes

After making any changes, apply the configuration using:

sudo Netplan apply

Step 3: Check systemd-networkd Status

Verify that systemd-networkd is running correctly:

sudo systemctl status systemd-networkd

Look for any error messages that might indicate issues with the network configuration.

Step 4: Test DNS Resolution

Use the dig or nslookup command to test DNS resolution:

dig google.com

If the command returns an error, it indicates a DNS resolution failure.

Step 5: Check Network Connectivity

Ensure that your system can reach the DNS servers. Use the ping command:

ping 8.8.8.8

If the ping fails, there may be a network connectivity issue.

Step 6: Review Firewall Settings

Check if any firewall rules are blocking DNS traffic (UDP port 53). Use:

sudo iptables -L -n

Look for rules that might be affecting DNS traffic.

Practical Examples

Consider a scenario where a server is unable to resolve domain names. After following the steps outlined above, you discover that the DNS server IP was incorrectly configured in the Netplan file. Correcting the IP address and reapplying the configuration resolves the issue.

Best Practices for DNS Configuration

Always use reliable DNS servers, such as Google (8.8.8.8) or Cloudflare (1.1.1.1).
Implement redundancy by specifying multiple DNS servers in your configuration.
Regularly monitor DNS resolution performance and logs for anomalies.
Document your network configuration changes for future reference.

Case Studies and Statistics

A study by the Internet Society found that 30% of organizations experience DNS-related outages at least once a year. By following best practices and maintaining a robust DNS configuration, organizations can significantly reduce the risk of such failures.

Conclusion

Debugging DNS resolution failures in Netplan and systemd-networkd requires a systematic approach to identify and resolve issues. By following the steps outlined in this guide, network administrators can ensure reliable DNS functionality, enhancing the overall stability and performance of their networked systems. Remember to apply best practices and regularly monitor your configurations to prevent future issues.