How Wake-on-LAN Works
When a computer is "off," its network card is not always completely dead. With Wake-on-LAN enabled, the network interface card (NIC) keeps a trickle of standby power and stays in a low-power listening mode while the rest of the system is shut down or asleep. It is waiting for one specific thing: a magic packet addressed to it.
When that packet arrives, the NIC recognises the pattern and signals the motherboard to power the machine on, exactly as if you had pressed the power button. The whole point is that no other part of the computer needs to be running — only the network card, sipping standby power, has to stay alert.
The Magic Packet
The trigger is deliberately distinctive so the NIC cannot mistake ordinary traffic for a wake request. A magic packet is a frame containing:
- Six bytes of
0xFF(a synchronisation stream), followed by - the target device's MAC address repeated 16 times in a row.
Because the packet is keyed to the MAC address — the hardware identifier burned into the NIC — it does not rely on the machine having an IP address yet (it has none while off). The packet is almost always sent as a UDP datagram to port 7 or 9, broadcast across the local network so it reaches the sleeping card.
What You Need to Enable It
Wake-on-LAN usually has to be switched on in two separate places, and both are required:
- BIOS/UEFI firmware. Reboot into your motherboard's setup and look under power management for an option named Wake on LAN, Power On by PCI-E/PCI, Resume by LAN, or similar. Enable it. Some systems also need "deep sleep" or "ErP" power-saving modes disabled, since those cut power to the NIC entirely.
- Operating system network adapter. In the NIC's properties, allow the device to wake the computer and to respond to a magic packet. On Windows this lives in Device Manager under the adapter's Power Management and Advanced tabs; Linux uses
ethtool(thewol gsetting); macOS exposes it as "Wake for network access."
Two practical requirements matter a great deal:
- Use wired Ethernet. WoL is most reliable over a cable. A Wi-Fi equivalent (WoWLAN) exists but is inconsistent — many wireless adapters drop their connection on sleep and never hear the packet.
- Leave the cable and NIC powered. The card needs standby power, so the machine must be connected and the power supply must keep feeding the NIC when off.
Waking a Device on Your Local Network
On the same network, sending a magic packet is simple. A WoL utility (desktop apps, phone apps, router built-ins, or command-line tools) asks for the target's MAC address and broadcasts the packet across the LAN. Within a second or two, the target boots. You can find a device's MAC address ahead of time using the methods in how to find a MAC address — note it down while the machine is still on, since you will need it when the machine is off.
Waking a Device Over the Internet
Waking a machine from outside your home is the part that trips people up. A magic packet is a local broadcast, and routers do not forward broadcasts between networks by default — so a packet sent from the internet has nothing to land on. There are three common ways around this:
| Method | How it works | Trade-off |
|---|---|---|
| Port forwarding | Forward a UDP port on your router to the target, often paired with a static ARP entry mapping its IP to its MAC. | Needs a public IP; fiddly, and blocked by CGNAT. |
| VPN into your home | Connect to a VPN server on your network, then send the packet as if you were local. | Cleanest and most secure; needs a VPN endpoint that stays on. |
| Always-on relay | A low-power device (router, mini-PC, NAS) that is always on receives your request and broadcasts the magic packet locally. | Requires one device left running. |
The VPN approach is generally the most reliable and secure, because it avoids exposing anything directly to the internet and sidesteps the broadcast-routing problem entirely. If you rely on port forwarding instead, remember it will not work behind carrier-grade NAT.
What People Use It For
- Home servers and NAS — keep a media server or backup box powered off, and wake it only when you actually need a file or a stream, cutting idle power use.
- Remote desktop — boot a desktop from afar before connecting in, rather than leaving it on all day.
- Occasional-use workstations — a powerful editing or gaming PC that is wasteful to idle but inconvenient to walk over and switch on.
Troubleshooting
- Nothing happens: confirm WoL is enabled in both BIOS and the OS, and that "deep sleep"/ErP power saving is off.
- Works from sleep but not full shutdown: some systems only support waking from sleep states; check for a "shutdown WoL" or "S5 wake" option in firmware.
- Wi-Fi won't wake: switch to wired Ethernet — this is the single most common fix.
- Works locally, not remotely: the broadcast isn't reaching the target — use a VPN or relay rather than wrestling with port forwarding.
Frequently Asked Questions
What is Wake-on-LAN?
A standard that lets you power on a sleeping or shut-down computer by sending it a magic packet over the network. The NIC stays partly powered, listens for the packet, and signals the motherboard to boot.
What is a magic packet?
The frame that triggers WoL: six bytes of 0xFF followed by the target's MAC address repeated 16 times, usually sent as UDP to port 7 or 9. The NIC recognises this pattern even while the machine is off.
How do I enable Wake-on-LAN?
Enable it in the BIOS/UEFI (Wake on LAN / Power On by PCI-E) and in the OS network adapter settings (allow the device to wake the computer on a magic packet). Use wired Ethernet for reliability.
Can Wake-on-LAN work over the internet?
Yes, with extra setup, because the magic packet is a local broadcast routers don't forward. Use port forwarding with a static ARP entry, a VPN into your home, or an always-on relay device that broadcasts the packet locally.
Does Wake-on-LAN work over Wi-Fi?
There is a variant (WoWLAN), but it is far less reliable than wired WoL and depends on the adapter and driver. Many Wi-Fi cards drop the connection on sleep. Use Ethernet for dependable wake-ups.