Wake-on-LAN

Wake-on-LAN (WoL) powers on a machine by sending it a “magic packet”: 6 bytes of FF followed by the target MAC address repeated 16 times, normally in a UDP broadcast to port 9 (some tools use 7). It needs support in the BIOS/UEFI and the network card, and the card must stay powered while the machine is off. It is layer 2, so crossing VLANs needs a directed broadcast or a relay.

Documentation: ethtool man page · Netplan reference (wakeonlan) · systemd.link

Verification: commands and snippets were written from the upstream documentation and not executed. Behaviour depends heavily on NIC, driver and firmware, so test with the machine fully shut down, not just suspended.

See also: Homelab · VLANs · Proxmox Networking · Proxmox qm and pct · NUT (Network UPS Tools) · Tailscale · WireGuard

Target Machine Setup #

1. Enable Wake on LAN / Power on by PCIe in BIOS/UEFI. Disable “ErP/EuP” or deep-power-saving options that cut standby power to the NIC.
2. Find the interface name and MAC: ip -br link.
3. Enable magic-packet wake in the driver (below) and make it persistent.

ethtool letters: p PHY activity, u unicast, m multicast, b broadcast, a ARP, g magic packet, s SecureOn password, d disabled.

The setting is lost on reboot on many systems; persist it one of these ways.

systemd-networkd .link file #

/etc/systemd/network/50-wol.link:

[Match]
MACAddress=aa:bb:cc:dd:ee:ff

[Link]
WakeOnLan=magic

Reboot (or sudo udevadm trigger -c add -s net) to apply.

Netplan #

network:
  version: 2
  ethernets:
    eno1:
      dhcp4: true
      wakeonlan: true

sudo netplan apply

NetworkManager #

nmcli -f 802-3-ethernet.wake-on-lan connection show "<CONNECTION>"
nmcli connection modify "<CONNECTION>" 802-3-ethernet.wake-on-lan magic
nmcli connection up "<CONNECTION>"

Proxmox / ifupdown #

In /etc/network/interfaces, under the physical NIC that is a bridge port:

iface eno1 inet manual
    post-up /usr/sbin/ethtool -s eno1 wol g

Apply with ifreload -a. See Proxmox Networking. Proxmox can also start guests on a schedule or by API (Proxmox qm and pct), which is often easier than waking the host; wake the node with WoL, then start its VMs.

Windows #

Device Manager -> network adapter -> Properties: Advanced “Wake on Magic Packet” enabled, Power Management “Allow this device to wake the computer” and “Only allow a magic packet to wake the computer”. Disable Fast Startup, which often breaks WoL after a shutdown.

Sending a Magic Packet #

Python with no extra package:

python3 - <<'EOF'
import socket
mac = bytes.fromhex("aabbccddeeff")
pkt = b"\xff" * 6 + mac * 16
with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
    s.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
    s.sendto(pkt, ("192.168.20.255", 9))
EOF

Docker (no install on the sender):

docker run --rm --network host alpine:3 sh -c 'apk add -q wakeonlan && wakeonlan <MAC>'

Host networking is needed so the broadcast leaves on the real LAN.

Waking Across VLANs and Remotely #

Web front-ends such as a small WoL container or Home Assistant’s wake_on_lan integration give a button without SSH; whichever you use, keep it internal-only (Reverse Proxy Patterns).

Check That the Machine Woke #

wakeonlan <MAC> && until ping -c1 -W1 <HOST_IP> >/dev/null 2>&1; do sleep 2; done && echo up

Watch for the packet arriving on a sibling machine: sudo tcpdump -ni <IFACE> 'udp port 9 or ether proto 0x0842' (0x0842 is the raw WoL EtherType used by etherwake).

Troubleshooting #