History

In April of 1997, the IBM Advanced Manageability Alliance released the first glimpse of Wake on LAN technology. Other industry initiatives, such as Intel-based Wired for Management, soon supported the standard.

Technical details

System requirements

Wake on LAN support is implemented in the motherboard of the computer. The motherboard must have a WAKEUP-LINK header onboard and connected to the network card via a special 3-pin cable; however, systems supporting the PCI 2.2 standard coupled with a PCI 2.2 compliant network adapter typically do not require a WOL cable as the required standby power is relayed through the PCI bus. Wake on LAN must also be enabled in the Power Management section of the motherboard's BIOS. It may also be necessary to configure the computer to reserve power for the network card when the system is shut down.

The general process of waking a computer up remotely in a LAN can be explained as such:

The target computer is shut down, with power reserved for the network card. The network card listens for a specific packet, called the Magic Packet. The Magic Packet is broadcasted on the broadcast address for that particular subnet or the entire LAN. The listening computer receives this packet, checks it for the correct information, and then boots if the Magic Packet is valid.

The Magic Packet is a broadcast frame, transmitted over port 7 or 9. It can be sent over a variety of connectionless protocols (UDP, IPX) but UDP is most commonly used. The data that is contained in a Magic Packet is the defined constant as represented in hexadecimal: FF FF FF FF FF FF followed by sixteen repetitions of the target computer's MAC address, possibly followed by a four or six byte password.