Network Configuration with Netplan

Overview

• What you’ll learn: How Netplan works as Ubuntu’s network configuration layer, YAML syntax for defining interfaces, static and DHCP addressing, routes, DNS, bonds, VLANs, and how to apply and troubleshoot configurations.
• Prerequisites: Lesson 14 – Routing and Switching Basics
• Estimated reading time: 20 minutes

Introduction

Network configuration on Linux has historically been managed through a variety of tools and file formats — from /etc/network/interfaces on Debian to NetworkManager on desktop systems. Ubuntu 17.10 introduced Netplan, a unified, declarative YAML-based configuration layer that sits above the underlying network daemons (systemd-networkd or NetworkManager).

Netplan simplifies network configuration by providing a single, consistent syntax regardless of which backend renderer is used. You describe the desired network state in YAML files, and Netplan generates the appropriate configuration for the backend. This approach is especially powerful for cloud deployments and automated provisioning.

In this lesson, you will learn the Netplan architecture, master the YAML configuration syntax, configure common networking scenarios, and learn how to apply, test, and troubleshoot your configurations.

Netplan Architecture

Netplan operates as a translation layer between your YAML configuration files and the underlying network renderer. Configuration files are stored in /etc/netplan/ and are processed in lexicographic order. Netplan supports two backend renderers: systemd-networkd (default on Ubuntu Server) and NetworkManager (default on Ubuntu Desktop).

# List existing Netplan configuration files
$ ls /etc/netplan/
01-netcfg.yaml

# View the current configuration
$ cat /etc/netplan/01-netcfg.yaml
network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: true

# View what Netplan will generate (dry run)
$ sudo netplan generate

# Show the current network state as Netplan sees it
$ sudo netplan status
     Online state: online
    DNS Addresses: 192.168.1.1
       DNS Search: localdomain

●  1: lo -- Software Loopback (Unmanaged)
●  2: ens33 -- Ethernet (networkd: ens33)
      MAC Address: 00:0c:29:ab:cd:ef
        Addresses: 192.168.1.10/24
      DNS Servers: 192.168.1.1
           Routes: default via 192.168.1.1

Static IP Configuration

The most common Netplan task is assigning a static IP address. You specify the interface, disable DHCP, and provide the address, gateway, and DNS servers.

# /etc/netplan/01-netcfg.yaml — Static IP configuration
network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: no
      addresses:
        - 192.168.1.10/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        search: [example.com]
        addresses: [8.8.8.8, 8.8.4.4]

# Apply the configuration
$ sudo netplan apply

# Verify the new IP address
$ ip addr show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
    inet 192.168.1.10/24 brd 192.168.1.255 scope global ens33

# Verify the default route
$ ip route show
default via 192.168.1.1 dev ens33 proto static
192.168.1.0/24 dev ens33 proto kernel scope link src 192.168.1.10

# Verify DNS resolution
$ resolvectl status ens33
Link 2 (ens33)
    Current Scopes: DNS
    DNS Servers: 8.8.8.8 8.8.4.4
    DNS Domain: example.com

Multiple Interfaces and Routes

Servers often have multiple network interfaces — for example, one for public traffic and another for a private management network. Netplan makes it easy to configure each interface independently with its own addresses, routes, and DNS settings.

# /etc/netplan/01-netcfg.yaml — Multiple interfaces
network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: no
      addresses:
        - 192.168.1.10/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8]
    ens34:
      dhcp4: no
      addresses:
        - 10.0.0.10/24
      routes:
        - to: 10.10.0.0/16
          via: 10.0.0.1
        - to: 172.16.0.0/12
          via: 10.0.0.254

# Apply and verify
$ sudo netplan apply
$ ip route show
default via 192.168.1.1 dev ens33 proto static
10.0.0.0/24 dev ens34 proto kernel scope link src 10.0.0.10
10.10.0.0/16 via 10.0.0.1 dev ens34 proto static
172.16.0.0/12 via 10.0.0.254 dev ens34 proto static
192.168.1.0/24 dev ens33 proto kernel scope link src 192.168.1.10

Bonding and VLANs

For high availability and network segmentation, Netplan supports interface bonding (combining multiple physical interfaces into one logical interface) and VLANs (virtual LANs that segment traffic on the same physical network).

# /etc/netplan/01-netcfg.yaml — Bond configuration
network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: no
    ens34:
      dhcp4: no
  bonds:
    bond0:
      interfaces: [ens33, ens34]
      addresses:
        - 192.168.1.10/24
      routes:
        - to: default
          via: 192.168.1.1
      parameters:
        mode: 802.3ad
        lacp-rate: fast
        mii-monitor-interval: 100

# VLAN configuration
network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: no
  vlans:
    vlan100:
      id: 100
      link: ens33
      addresses:
        - 10.100.0.10/24
    vlan200:
      id: 200
      link: ens33
      addresses:
        - 10.200.0.10/24

Testing and Troubleshooting

Netplan provides a safe way to test configurations before committing them. The netplan try command applies changes temporarily and automatically reverts if you do not confirm within a timeout period.

# Test a configuration with automatic rollback (default 120 seconds)
$ sudo netplan try
Do you want to keep these settings?

Press ENTER before the timeout to accept the new configuration

Changes will revert in 118 seconds

# Validate YAML syntax without applying
$ sudo netplan generate
# (No output means success; errors are printed if YAML is invalid)

# Debug mode — see exactly what Netplan generates
$ sudo netplan --debug generate
DEBUG: Processing /etc/netplan/01-netcfg.yaml
DEBUG: Generating output files...

# Check systemd-networkd status
$ networkctl status ens33
● 2: ens33
       Link File: /usr/lib/systemd/network/99-default.link
    Network File: /run/systemd/network/10-netplan-ens33.network
            Type: ether
           State: routable (configured)
         Address: 192.168.1.10
         Gateway: 192.168.1.1
             DNS: 8.8.8.8

Key Takeaways

• Netplan is Ubuntu’s declarative YAML-based network configuration system that generates configs for systemd-networkd or NetworkManager backends.
• Configuration files in /etc/netplan/ define interfaces, addresses, routes, DNS, bonds, and VLANs in a clean, readable format.
• Use sudo netplan apply to activate changes, and sudo netplan try to test with automatic rollback for safety.
• Multiple interfaces can be configured independently, each with their own static addresses, routes, and nameservers.
• Always validate with sudo netplan generate before applying, and use networkctl status to verify the result.

What’s Next

In Lesson 16, you will learn DNS Fundamentals — how the Domain Name System translates human-readable names to IP addresses, the DNS hierarchy, record types, and tools for querying DNS.