Ubuntu NetPlan

Preview

Netplan is Ubuntu’s standard way to declare networking in YAML and hand it off to a backend (“renderer”) like systemd-networkd or NetworkManager. Config lives under /etc/netplan/*.yaml, and Netplan can safely trial changes with automatic rollback.

Identify your interface before writing YAML

When a machine is fresh (or YAML isn’t there yet), quickly discover the real device names:

# List interfaces (names, state)
ip -br link

# Include addresses (IPv4/IPv6)
ip -br addr
ip -br -4 addr
ip -br -6 addr

# Drill into a specific interface
ip addr show dev enp3s0
ip -br addr show dev enp3s0

• -br/--brief shows tidy tables; -j/--json gives machine-readable output.
• ip a is shorthand for ip addr. You only need show dev IFACE when narrowing to one device; for listing, show isn’t required.

Minimal recipes

Put one of these under /etc/netplan/01-net.yaml, then sudo netplan try → confirm → sudo netplan apply.

1) DHCP (server-style)

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      dhcp4: true

2) Static IPv4 + DNS + default route

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      addresses: [10.10.10.20/24]
      nameservers:
        search: [corp.local]
        addresses: [10.10.10.253, 8.8.8.8]
      routes:
        - to: default
          via: 10.10.10.1

3) Multiple gateways (primary/backup via metrics)

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      addresses: [10.0.0.10/24]
      routes:
        - to: default
          via: 10.0.0.1
          metric: 100
        - to: default
          via: 10.0.1.1
          metric: 200

4) Bridge (commonly for KVM/containers)

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0: { dhcp4: false }
  bridges:
    br0:
      dhcp4: true
      interfaces: [enp3s0]

5) Bond (active-backup or 802.3ad/LACP)

network:
  version: 2
  renderer: networkd
  bonds:
    bond0:
      interfaces: [enp3s0, enp4s0]
      dhcp4: true
      parameters:
        mode: active-backup # or: 802.3ad

6) VLAN (tagged subinterface)

network:
  version: 2
  renderer: networkd
  ethernets:
    mainif: { dhcp4: false }
  vlans:
    vlan15:
      id: 15
      link: mainif
      addresses: [10.3.99.5/24]

7) Wi-Fi (desktop/laptop; use NetworkManager)

network:
  version: 2
  renderer: NetworkManager
  wifis:
    wlp2s0:
      access-points:
        "MY_SSID":
          password: "********"
      dhcp4: true

Safe-apply workflow (remote friendly)

1. Inspect the merged config:

sudo netplan get

1. Trial with auto-rollback:

sudo netplan try   # default 120s countdown

1. Commit:

sudo netplan apply

If you lose connectivity during step 2, Netplan restores the previous state automatically after the timeout—exactly what you want over SSH.

Troubleshooting checklist

• netplan status [IFACE] (add --diff to compare YAML vs live).
• Verbose apply: sudo netplan --debug apply.
• IP/Routes: ip -br addr, ip route.
• DNS: resolvectl status.
• Logs: journalctl -u systemd-networkd or journalctl -u NetworkManager.
• Netplan itself recommends using ip addr to see actual IP state.

About cloud images & generated YAML

On cloud images you’ll often find a generated file like /etc/netplan/50-cloud-init.yaml. Your platform (cloud-init, MAAS, etc.) may own networking until you switch it to Netplan-only or adjust its template. The key is knowing Netplan reads all YAML from /{lib,etc,run}/netplan and merges them lexicographically—later files amend/override earlier ones.

Appendix: iproute2 one-liners

# Interface names only
ip -o link show | awk -F': ' '{print $2}'

# IPv4 per NIC (comma-separated)
for i in $(ls /sys/class/net | grep -v lo); do
  printf "%-12s %s\n" "$i" "$(ip -4 -o addr show dev $i | awk '{print $4}' | paste -sd, -)"
done

# JSON (good for scripts)
ip -j addr show | jq .

• -br/--brief for compact tables, -j/--json for machine-readable, and object names can be abbreviated (ip addr → ip a).