Wake-on-LAN: how to turn on a computer or server remotely

Need to reach a computer at home or at work, but it is turned off? You do not need someone to go turn it on for you. Wake-on-LAN serves this purpose. Let us explain what it is, how it works and when it is useful.

What Wake-on-LAN is

Wake-on-LAN (WoL for short) is a feature that lets you turn on a computer remotely over the network. The computer looks turned off, but its network card stays on standby and listens. When it receives a special “wake” message, the computer turns on.

This wake message is called a magic packet. It is a small network packet addressed to a specific computer that wakes it up.

How it works

1. The computer has Wake-on-LAN enabled in the BIOS and the network card.
2. Even when off, the network card is powered and waits for a signal.
3. From another device (smartphone, laptop) you send a magic packet.
4. The computer turns on as if you had pressed the button.

Within one network this is straightforward. To turn it on over the internet from afar, additional setup is needed, most securely via VPN, or via port forwarding.

What to set up

• Enable WoL in the computer’s BIOS.
• Enable WoL in the network card settings in the operating system.
• A cable connection is more reliable. Over WiFi, WoL works only in a limited way.
• An app or router that can send the magic packet.

It sounds like a few steps, but the details vary by hardware and it is often easier to have it set up for you.

A practical step-by-step guide

Let us walk through the setup on an ordinary Windows computer. On other systems the principle is the same, only the names of the options differ.

1. Enter the BIOS/UEFI. Right after powering on, keep pressing Delete or F2 (it varies by manufacturer). In the Power Management section look for an option such as “Wake on LAN”, “Power On by PCI-E” or “Resume by LAN” and enable it.
2. Disable power-saving features that cut power to the network card. Leave options such as “ErP Ready” or “Deep Sleep” turned off, otherwise the card loses power once the computer shuts down and has nothing to listen with.
3. Open Device Manager in Windows, expand Network adapters and open the properties of your card. On the Power Management tab allow “Allow this device to wake the computer” and in the Advanced settings enable “Wake on Magic Packet”.
4. Turn off Fast Startup. This feature in the Windows power settings means that a “shut down” Windows is actually in a special hibernation state from which WoL does not work on many boards.
5. Find the MAC address of the network card. In the command prompt run ipconfig /all and note the Physical Address line. That is the address the magic packet is sent to.
6. Test the wake-up within your home network. Install a magic packet app on a smartphone or another computer, enter the MAC address and try waking the machine. Only once it works at home should you deal with access from outside via VPN.

Which states the computer can be woken from

After a power outage some boards “forget” the setting until the computer boots normally once. If remote power-on matters to you, it is worth protecting the machine with backup power (a UPS).

Where Wake-on-LAN is worth it

• Working from home. You turn on your work computer in the office and connect to it.
• A home server or NAS that need not run all the time and you turn on only when you need it, saving energy.
• Remote management and service. A technician wakes the computer, does maintenance and puts it back to sleep.
• Access to files you have only on your home computer.

Advantages

• Energy saving. The computer need not run nonstop, you turn it on only when needed.
• Convenience. Access to the device even when you are elsewhere.
• No other person. You do not need anyone to physically turn the computer on for you.

Common mistakes and myths

• “Enabling it in the BIOS is enough.” It is not. WoL must also be enabled on the network card in the operating system, otherwise the computer wakes at best from sleep, not from a powered-off state.
• “WoL drains the computer.” A network card on standby draws under 1 W, a fraction of what a running computer uses.
• “A magic packet turns on any computer on the network.” It does not. The packet contains the MAC address of one specific card and only that card reacts to it.
• “It works the same over WiFi as over cable.” It does not. When the computer is off, the WiFi module is usually unpowered, which is why we always recommend a cable for WoL.
• “It will just work from the internet.” It will not. A router does not pass the wake broadcast in from the internet; you need a VPN or a targeted setup.

When the computer will not wake: troubleshooting

• Look at the network card’s indicator light. If it is dark and not blinking while the computer is off, the card has no power. Check ErP/Deep Sleep in the BIOS.
• Turn off Fast Startup in Windows. It is the most common reason WoL fails from a “powered-off” state.
• Check the settings after updates. A Windows update occasionally reinstalls the network card driver and the wake permissions revert to defaults.
• Verify the MAC address. One wrong character and the packet wakes nobody. Also make sure you are targeting the card the computer is actually connected through.
• Test remote wake-up in stages. First confirm WoL works within the home network, only then over VPN. That narrows down the possible causes.

Security at the end

When turning on over the internet, think about security. Do not open ports to the internet unnecessarily, rather use a VPN. This also relates to securing the router.

This article is part of our Computer networks overview.