Wake on LAN is a networking standard that lets you turn on a powered-off or sleeping computer by sending it a magic packet. The magic packet is a broadcast frame carrying six bytes of all ones followed by the target computer's MAC address repeated sixteen times.
While the machine is off, its network card stays partly powered and listening; when it sees a magic packet addressed to its own MAC, it signals the motherboard to power on.
Because the packet is a layer 2 broadcast keyed to the MAC rather than the IP, wake on lan works within one subnet by default and needs extra setup to cross subnets or the internet.
- Wake on LAN turns on an off or sleeping computer over the network
- The trigger is a magic packet: six 0xFF bytes then the MAC repeated 16 times
- The network card stays partly powered and listens while the machine is off
- It is a layer 2 broadcast keyed to the MAC, so it works within one subnet by default
- It must be enabled in BIOS or UEFI and in the network card settings
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What it isWhat wake on lan is
WoL solves a small but real problem: reaching a device that is not on.
It powers a machine on remotely. Wake-on-LAN is an Ethernet networking standard that allows a computer to be turned on or awakened from sleep by a network message. It is how an administrator patches a room of desktops overnight, or how you reach a home machine that you left asleep.
It works because the card never fully sleeps. When the computer is off or sleeping, its network interface card stays in a low-power state, still drawing a little power and watching the wire. To save energy further, the Ethernet link is usually dropped to its lowest speed. The card is doing one job: waiting for the magic packet.
It is a WoL hardware feature, not software. The wake happens below the operating system. The card sees the packet and signals the motherboard to power up, so the machine can be completely shut down, not just asleep, and still respond, as long as the hardware and firmware support it.
The magic packetThe magic packet
The whole mechanism turns on one specially shaped frame.
It has a fixed signature. The magic packet is a frame, most often sent as a broadcast, that contains somewhere in its payload six bytes of all ones, FF FF FF FF FF FF in hexadecimal, followed by sixteen repetitions of the target computer's 48-bit MAC address, for a total of 102 bytes. The card scans incoming traffic for exactly that pattern.
It identifies the target by MAC, not IP. The packet is addressed to the machine's MAC address, not its IP address. That is why you wake a machine by its MAC: while it is off it has no active IP, but its MAC is burned into the card and the card is still listening.
It is usually carried in a broadcast. Because the target has no active IP, the packet is normally sent to the network broadcast address so every device on the Ethernet segment sees it, and only the card whose MAC matches acts.
It commonly rides in a UDP datagram to port 7 or port 9, though the port does not matter to the card, only the payload signature does.
Where it reachesHow wake on lan travels the network
Where the packet can reach is the part that trips people up.
Within a subnet it just works. On the same broadcast domain, the broadcast reaches every device, so waking a machine on your own LAN generally has no issues. This is the common case and needs no special routing.
Across subnets it needs help. Routers do not forward broadcasts by default, so a magic packet does not naturally cross from one subnet to another. Waking a machine in a different segment requires a subnet-directed broadcast, or a device on that segment to relay the packet.
Over the internet it needs forwarding. Reaching a machine from outside the network means either a subnet-directed broadcast through the router or port forwarding from the public address to the target segment. This is wake on lan over the internet, and it is more fragile because it depends on the router passing WoL packets inward correctly.
Enabling itTurning it on
WoL is off until several pieces are enabled together.
Enable it in firmware. The WoL setting lives in the BIOS or UEFI, often named Wake-on-LAN, Power on by PCIe, or similar. Without it, the card is not kept powered while the machine is off and nothing will wake it.
Enable it on the network card. In the operating system, the network adapter's power management has to allow the card to wake the computer, and specifically to wake on a magic packet rather than on any traffic. Both firmware and the driver setting have to agree.
Know the target's MAC. Because the wake is keyed to the MAC address, whatever tool sends the WoL magic packet needs that device MAC. On a managed network this is inventoried; at home it is read once from the machine while it is on.
Enabling wake on lan in Windows and Linux
In Windows the WoL setting sits on the network interface card (NIC). Open Device Manager, open the properties of the network adapter, and on the Power Management tab allow this device to wake the computer. Then select the option to only allow a magic packet to wake it, so ordinary packets do not.
The Advanced tab of the same adapter usually lists a Wake on Magic Packet property, and it has to be enabled too. On Linux the NIC setting is read and changed with ethtool, where a Wake-on value of g means the interface wakes on magic packets.
Which power states WoL can wake a system from
How does wake on lan work after a shutdown in Windows? Often it does not. Microsoft's article on WOL behavior says Windows 10 shuts down by default into hybrid shutdown, also known as Fast Startup, power state S4. Network adapters are then explicitly not armed, and WOL from S4 or S5 is unsupported.
The same article says WOL is supported from sleep (S3), or from hibernate when the user requests it explicitly. It adds that the firmware on some systems can arm the NIC for wake from S4 or S5 without Windows being involved, which is why results differ from one device to the next.
Clearing the fast startup check box, under Power Options in Control Panel, is the documented way to disable the S4 state. Microsoft also says it does not recommend disabling it, so test the wake from shutdown before relying on WoL for remote access.
UsesWhat wake on lan is used for
The feature is small, but the jobs it enables are the reason it is built into almost every business network card.
Overnight maintenance. With a WoL tool or a remote management system, an administrator can wake a fleet of devices on a schedule, push patches or updates, and let them sleep again, without anyone leaving their machine on all night. WoL is what makes unattended, out-of-hours management possible across many devices at once.
Remote access to your own machine. Waking a computer before you connect means you can leave it asleep and still have access to it. A common pattern is to send the magic packet, wait for the machine to boot, then open a remote session, so the device is only powered up when you actually need it.
Saving energy. Because WoL lets a computer sleep or shut down and still be reachable, it removes the reason people leave machines running around the clock. A device that can be woken on demand can safely be powered down the rest of the time.
Centralized control of many endpoints. On a managed network, WoL turns a room full of Ethernet-connected computers into something that can be powered up as a group from one console, which is far more practical than walking to each machine.
PitfallsWhere people go wrong
Trying to wake by IP alone. A sleeping machine has no active IP, so the wake has to target the MAC. Tools that ask for an IP are really using it only to pick the broadcast address; the MAC is what identifies the machine.
Expecting it to cross a router. Broadcasts stop at the router. A magic packet sent from another subnet or the internet needs a subnet-directed broadcast or port forwarding, and forgetting this is the most common reason a wake silently does nothing.
Enabling firmware but not the driver, or the reverse. Both the BIOS or UEFI setting and the operating system's network card power setting have to be on. One without the other leaves the card either unpowered or not configured to wake, and the packet is ignored.
Fast startup hiding the setting. On some systems an aggressive shutdown or fast-boot mode cuts power to the NIC, so WoL works from the sleep state but not from a full shutdown. The behavior depends on the firmware and the shutdown mode.
Assuming it is secure by default. The basic magic packet carries no authentication; anyone on the segment who knows a MAC can wake the machine. Some cards support a password in the packet, but plain WoL is a convenience feature, not a secured one.
ComparisonWake on LAN, the essentials
| Criterion | Detail |
|---|---|
| Standard | Ethernet wake-on-LAN |
| Trigger | Magic packet frame |
| Signature | 6 bytes of 0xFF, then the MAC 16 times, 102 bytes |
| Addressed by | MAC address, not IP |
| Transport | Broadcast, commonly UDP port 7 or 9 |
| Default reach | The local subnet or broadcast domain |
| To cross subnets | Subnet-directed broadcast or a relay |
| To enable | BIOS/UEFI plus network card power settings |
The two things to remember are that the packet is keyed to the MAC, and that as a broadcast it stays inside one subnet unless the network is set up to carry it further.
FAQFrequently asked questions
What is wake on lan?
A networking standard that lets you turn on a powered-off or sleeping computer by sending it a network message called a magic packet. The computer's network card listens for that packet while the machine is off and powers the machine on when it arrives.
What is a magic packet?
The frame that triggers a wake. It contains six bytes of all ones, FF FF FF FF FF FF, followed by the target computer's MAC address repeated sixteen times, 102 bytes in total. The network card scans traffic for exactly this pattern.
What port does wake on lan use?
The magic packet is commonly sent in a UDP datagram to port 7 or port 9, but the port is not what matters. The card acts on the payload signature, not the port, so any port can carry it.
Does wake on lan work over the internet?
It can, but not by default. Because the magic packet is a broadcast that routers do not forward, waking a machine from the internet needs a subnet-directed broadcast or port forwarding on the router to deliver the packet to the right segment.
Why does wake on lan use the MAC address?
Because a machine that is off has no active IP address. Its MAC address is fixed in the network card, and the card is the only part still powered, so the wake has to be keyed to the MAC.
How do I enable wake on lan?
Turn it on in the BIOS or UEFI, then allow the network card to wake the computer in the operating system's adapter power settings, specifically on a magic packet. Both the firmware and the driver setting have to be enabled.
Does the computer have to be plugged in?
Yes. The network card keeps drawing a small amount of standby power while the machine is off, so wake on lan needs the machine connected to power, and for wired cards, connected to the network.
Can wake on lan turn on a fully shut-down PC?
Usually yes, if the hardware and firmware support it and the setting is enabled. Some systems with aggressive fast-startup or shutdown modes cut power to the card, so it wakes from sleep but not from a full shutdown.
Does wake on lan work over Wi-Fi?
Standard wake on lan is a wired Ethernet feature. There is a wireless variant, sometimes called Wake on Wireless LAN, but it needs specific hardware and driver support and is less widely available than the wired version.
Is wake on lan secure?
The basic magic packet has no authentication, so anyone on the same network segment who knows a machine's MAC can wake it. Some cards support a password in the packet, but plain wake on lan is a convenience feature and should be treated as one.
Why is my wake on lan not working?
The usual causes are the setting being enabled in only one of firmware or the driver, trying to wake across a router without a directed broadcast, a fast-startup mode cutting card power, or sending to the wrong MAC or broadcast address.
What is the difference between wake on lan and remote desktop?
Wake on lan turns the machine on; remote desktop connects to a machine that is already running. They are often used together: wake on lan powers the machine up, then remote desktop logs in.
Where is the Wake on LAN BIOS setting?
The Wake on LAN BIOS setting is usually in the power management section of the firmware menu, under a name such as Wake on LAN, Power On by PCI-E, or Resume by LAN. It has to be enabled there and in the network adapter's driver settings in the operating system, or the magic packet is ignored.
Keep readingRelated concepts
Read next · Switching What Is a VLAN? The broadcast domain a magic packet stays within by default. Open this next14 min- Network fundamentals · 9 min Ethernet Frame Format, Field by Field The frame the magic packet rides inside, field by field.
- Switching · 9 min The MAC Address Table, and How to Find Which Port a Device Is On The MAC address the magic packet is keyed to, and how switches use it.