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Netplan

Netplan is a powerful utility that simplifies network configuration on modern Linux systems. It provides a declarative way to configure network interfaces using YAML files, replacing older methods such as ifconfig and /etc/network/interfaces.

What is Netplan?

Netplan is a configuration utility for easily managing and applying network settings. Introduced in Ubuntu 17.10, it serves as a bridge between system administrators and low-level networking tools like systemd-networkd and NetworkManager. With Netplan, you define your network configurations in YAML files, and it handles the backend integration with these renderers.

Key Features

  • Declarative Configuration: Network settings are defined in human-readable YAML files.
  • Renderer Independence: Supports both systemd-networkd and NetworkManager as backends.
  • Modern Networking: Supports advanced features like bridges, VLANs, and bonds.
  • Simplified Management: A single command (netplan apply) applies all configurations.

Why Use Netplan?

Netplan streamlines network configuration by:

  1. Reducing Complexity: YAML syntax is simpler and more intuitive compared to legacy methods.
  2. Centralizing Configurations: Consolidates all network settings in the /etc/netplan/ directory.
  3. Supporting Modern Networking: Provides built-in support for advanced features like DHCP, static IPs, bridges, and VLANs.

Netplan Configuration Files

Location of Configuration Files

Netplan configuration files are stored in the /etc/netplan/ directory. These files typically have a .yaml extension, such as 01-netcfg.yaml or 50-cloud-init.yaml.

Structure of a Netplan File

A basic Netplan configuration file contains:

  1. network: The root key that holds all network settings.
  2. version: Indicates the YAML schema version (currently version 2).
  3. ethernets, vlans, bonds, bridges: Define specific types of interfaces.

Example:

network:
  version: 2
  ethernets:
    enp0s3:
      dhcp4: true

Why Configuration Files Have Numbers

Files in /etc/netplan/ often have a prefix like 01-, 50-, etc., which determines the order in which they are applied. Lower numbers take precedence over higher numbers. For example:

  • 01-netcfg.yaml will override settings in 50-cloud-init.yaml if both define the same interface.

This numbering system allows you to prioritize and layer configurations.

Applying Configuration Files

After creating or modifying a configuration file, you must apply the changes using:

sudo netplan apply

You can test the configuration before applying it permanently:

sudo netplan try

What is a Renderer in Netplan?

The renderer determines how Netplan applies configurations to the system. Netplan supports two renderers:

  1. networkd (systemd-networkd): A lightweight backend suitable for servers and minimal installations.
  2. NetworkManager: A full-featured network manager typically used on desktops and laptops.

Specifying the Renderer

In the YAML file, you can specify the renderer globally or per interface. Example:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      dhcp4: true

Or assign a different renderer to specific interfaces:

network:
  version: 2
  ethernets:
    enp0s3:
      renderer: NetworkManager
      dhcp4: true

Advanced Options

Netplan also supports advanced configurations like:

  • Bonds: For link aggregation.
  • Bridges: For virtualized or containerized environments.
  • VLANs: For virtual LAN tagging.

Refer to specific guides for these configurations.

Troubleshooting Netplan

Validating Configuration Files

Ensure the YAML syntax is correct:

sudo netplan generate

Debugging Errors

Check logs for error messages:

journalctl -u systemd-networkd

Reverting Changes

If a configuration fails, Netplan will automatically revert to the previous working state when using netplan try.

Conclusion

Netplan simplifies network management on Linux systems, offering a modern, declarative approach to configuring interfaces. Understanding its YAML syntax, file ordering, and renderers allows you to unlock powerful networking capabilities while keeping configurations clean and manageable. For more details, refer to the Netplan Official Documentation.