Wake-on-LAN
The message is usually sent to the target computer by a program executed on a device connected to the same local area network (LAN).
If the computer being awakened is communicating via Wi-Fi, a supplementary standard called Wake on Wireless LAN (WoWLAN) must be employed.
[1] The WoL and WoWLAN standards are often supplemented by vendors to provide protocol-transparent on-demand services, for example in the Apple Bonjour wake-on-demand (Sleep Proxy) feature.
[3] It enabled a remote network device to be woken up through the underlying “power management circuitry”, by sending it a standard Ethernet frame, which “contains a specific data pattern detected by the Ethernet-controller on the receiving end”.
[3] Wake-on-LAN saw wide adoption starting in October 1996, when IBM formed the Advanced Manageability Alliance (AMA) with Intel.
[9] A connection-oriented transport-layer protocol like TCP is less suited for this task as it requires establishing an active connection before sending user data.
A standard magic packet has the following basic limitations: The Wake-on-LAN implementation is designed to be simple and to be quickly processed by the circuitry present on the network interface controller using minimal power.
[14] Wake-on-LAN can be a difficult technology to implement because it requires appropriate BIOS/UEFI, network interface hardware and, sometimes, operating system and router support to function reliably.
This means that due to hardware issues the computer may be wakeable from its soft off state (S5) but doesn't wake from sleep or hibernation or vice versa.
[16] This security measure significantly decreases the risk of successful brute force attacks, by increasing the search space by 48 bits (6 bytes), up to 296 combinations if the MAC address is entirely unknown.
Abuse of the Wake-on-LAN feature only allows computers to be switched on; it does not in itself bypass password and other forms of security, and is unable to power off the machine once on.
The use of Wake-on-LAN technology on enterprise networks can sometimes conflict with network access control solutions such as 802.1X MAC-based authentication, which may prevent magic packet delivery if a machine's WoL hardware has not been designed to maintain a live authentication session while in a sleep state.
AMT uses TLS encryption to secure an out-of-band communication tunnel to an AMT-based PC for remote management commands such as Wake-on-LAN.
[19][20] Because the encrypted communication is out-of-band, the PC's hardware and firmware receive the magic packet before network traffic reaches the software stack for the operating system (OS).
In order to get Wake-on-LAN to work, enabling this feature on the network interface card or on-board silicon is sometimes required.
[23] By supplying the pin-3 wake signal with +5V DC the computer will be triggered to power up provided WoL is enabled in the BIOS/UEFI configuration.
Software that sends a WoL magic packet is referred to in different circles as client or server, which can be a source of confusion.
Software to send WoL magic packets is available for all modern platforms, including Windows, Macintosh and Linux, plus many smartphones.
[citation needed] Example source code for a developer to add Wake-on-LAN to a program is readily available in many computer languages.
The following example is in Python: If the sender is on the same subnet or local area network as the computer to be awakened there are generally no issues.
When sending over the Internet, and in particular where a network address translation (NAT) router is involved (as typically in most homes), special settings are often necessary.
This allows the router to forward the magic packet to the sleeping computer at a networking layer below typical IP usage.
In the NAT router, ARP binding requires a dedicated IP and the MAC address of the destination computer.
Further configuration from the OS is required in some cases, for example via the Device Manager network card properties on Windows operating systems.
On laptops, the feature is controlled via the macOS System Settings Battery panel, in the Options pop-up window.
Additionally, a device which can switch the machine off and on again, controlled perhaps by a remote signal, can force a reboot which will clear problems due to misbehaving software.
If a connection delay of a minute or two is acceptable, the machine can timeout into hibernation, powered off with its state saved to disk.
The originator of the wakeup signal (magic packet) does not have to be on the same local area network (LAN) as the computer being woken.
