Wake-on-LAN
Encyclopedia
Wake-on-LAN is an Ethernet
computer networking standard that allows a computer to be turned on or woken up
by a network
message.
The message is usually sent by a program
executed on another computer on the same local area network
. It is also possible to initiate the message from another network by using Subnet directed broadcasts or a WOL gateway service. Equivalent terms include Wake On WAN, Remote Wake-up, Power On By LAN, Power Up By LAN, Resume by LAN, Resume on LAN, Wake Up On LAN. In case the computer being woken is communicating via Wi-Fi
, a supplementary standard called Wake on Wireless LAN (WoWLAN) must be employed.
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.
formed the Advanced Manageability Alliance(AMA). In April of 1997, this alliance introduced the Wake on LAN technology.
The term "Wake on LAN" is a trademark of IBM Corporation.
of the destination computer. The listening computer waits for a magic packet addressed to it and then initiates system wake-up.
The magic packet is sent on the data link or layer 2 in the OSI model
and broadcast to all NICs
using the network broadcast address
; the IP-address (layer 3 in the OSI model) is not used.
It is a common misconception that because Wake-on-LAN is built upon broadcast technology it can only be used within the current network subnet. While this is generally the case there are some exceptions.
In order for Wake-on-LAN to work, parts of the network interface need to stay on. This consumes standby power
, much less than normal operating power. If Wake-on-LAN is not needed, disabling it may reduce power consumption slightly while the computer is switched off but still plugged in.
containing anywhere within its payload 6 bytes of all 255 (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.
Since the magic packet is only scanned for the string above, and not actually parsed by a full protocol stack, it may be sent as any network- and transport-layer protocol, although it is typically sent as a UDP
datagram
to port
7 or 9, or directly over Ethernet as EtherType
0x0842
A standard magic packet has the following basic limitations:
The Wake-on-LAN implementation is designed to be very simple and to be quickly processed by the circuitry present on the network interface card (NIC) with minimal power requirement. Because Wake-on-LAN operates below the IP protocol layer the MAC address is required and makes IP addresses and DNS names meaningless.
.
In that case, software tools like a packet analyzer can help with Wake-on-LAN troubleshooting as they allow to confirm (while the PC is still on) that the magic packet is indeed seen by a particular computer's NIC. The same magic packet can then be used to find out if the computer powers up from an offline state. This allows networking issues to be isolated from other hardware issues. In some cases they also confirm that the packet was destined for a specific PC or sent to a broadcast address
and they can additionally show the packet's internals.
In Windows Vista and higher, you can also determine how the OS was powered up. You can use powercfg /lastwake in the CMD prompt and it will list the "Wake Source". The Wake-on-LAN event should also be logged in the System event log.
, which can be used or abused by anyone on the same LAN, unless the L2 LAN equipment is capable of (and configured for) filtering such traffic to match site-wide security requirements.
Firewalls may be used to prevent clients among the public WAN
from accessing the broadcast addresses of inside LAN segments, or routers may be configured to ignore subnet-directed broadcasts (see above.)
Certain NICs
support a security feature called "SecureOn". It allows users to store within the NIC
a hexadecimal password of 6 bytes. Clients have to append this password to the magic packet. The NIC
wakes the system only if the MAC address
and password are correct. This security measure significantly decreases the risk of successful brute force attack
s, by increasing the search space by 48 bits (6 bytes), up to 296 combinations if the MAC address is entirely unknown. However any network eavesdropping will expose the cleartext password.
Still, only a few NIC
and router manufacturers support such security features.
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.
to improve security for Wake-on-LAN. For example, Intel AMT
(a component of Intel vPro
technology), includes Transport Layer Security
(TLS), an industry-standard protocol that strengthens encryption
.
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. AMT secures the communication tunnel Advanced Encryption Standard
(AES) 128-bit encryption and RSA keys
with modulus lengths of 2,048 bits. 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). Since the encrypted communication occurs “below” the OS level, it is less vulnerable to attacks by viruses, worms, and other threats that typically target the OS level.
IT shops using Wake-on-LAN through the Intel AMT implementation can wake an AMT PC over network environments that require TLS-based security, such as IEEE 802.1x
, Cisco
Self Defending Network
(SDN), and Microsoft
Network Access Protection
(NAP) environments. The Intel implementation also works for wireless
networks.
(BIOS) of a computer and the network interface (firmware), and is consequently not dependent on the operating system (and NIC drivers) running on the hardware. Some operating systems can control Wake-on-LAN behaviour via hardware drivers. If the network interface is a plug-in card rather than being integrated into the motherboard, the card may need to be connected to the motherboard by an additional cable. Motherboards with an embedded Ethernet controller which supports Wake-on-LAN do not need a cable. The power supply must meet ATX
2.01 specifications.
via a special 3-pin cable; however, systems supporting the PCI 2.2 standard and with a PCI 2.2 compliant network adapter card do not usually require a Wake-on-LAN cable as the required standby power is relayed through the PCI bus.
PCI version 2.2 supports PME (Power Management Events). PCI cards send and receive PME signals via the PCI socket directly, without the need for a Wake-on-LAN cable.
Wake-on-LAN usually needs to be enabled in the Power Management section of a PC motherboard's BIOS setup utility, although on some systems, such as Apple computers, it is enabled by default. On older systems the bios setting may be referred to as "WOL", on newer systems supporting PCI version 2.2, it may be referred to as "PME" (Power Management Events, which include WOL). It may also be necessary to configure the computer to reserve standby power for the network card when the system is shut down.
In addition, in order to get Wake-on-LAN to work it is sometimes required to enable this feature on the network interface card or on-board silicon. Details of how to do this depend upon the operating system
and the device driver.
Laptops powered by the Intel Centrino Processor Technology or newer (with explicit BIOS support) allow waking up the machine using wireless Wake on Wireless LAN (WoWLAN).
In most modern PCs, ACPI
is notified of the "waking up" and take control of the Power up. In ACPI, OSPM must record the "wake source" or the device that is causing the power-up. The device being the "Soft" power switch, the NIC (via Wake-on-LAN), the cover being opened, a temperature change, etc.
The 3-pin WOL interface on the motherboard consist of pin-1 +5V DC (red), pin-2 Ground (black), pin-3 (green or yellow). By supplying +5V DC to the pin-3 wake signal with +5V DC the computer will be triggered to power up provided WOL is enabled in the BIOS
configuration.
for a developer to add Wake-on-LAN to a program is readily available in many computer languages.
Some home routers are able to send magic packets to LAN, for example routers with the DD-WRT
or Tomato
firmware have a built-in Wake On Lan client. The 3rd party FOSS project OpenWrt
supports both Linux implementations for WoL etherwake and wol.
Modern Mac hardware features integrated WoL functionality, controlled via the OS X System Preferences Energy Saver panel, in the Options tab. Marking the Wake for Ethernet network administrator access checkbox enables Wake-on-LAN.
Apple's Apple Remote Desktop
client management system can be used to send Wake-on-LAN packets, but there are also freeware and shareware Mac OS X applications available.
On Mac OS X Snow Leopard, the service is called Wake On Demand or Bonjour Sleep Proxy and is synonymous with the Sleep Proxy Service
. It comes enabled out of the box, but for previous versions of the operating system, the service will need to be enabled under the Energy Saver pane of System Preferences
. Your network interface card may allow the service to function only on WiFi, only on Ethernet, or both.
Since then many options have been added and standards agreed upon. A machine can be in 7 power states from S0 (fully on) through S5 (powered down but plugged in) and disconnected from power (G3, Mechanical Off), with names such as "sleep", "standby", and "hibernate". In some reduced-power modes the system state is stored in RAM and the machine can wake up very quickly; in others the state is saved to disk and the motherboard powered down, taking at least several seconds to awake. The machine can be woken from a reduced-power state by a variety of signals.
The machine's BIOS must be set to allow Wake-on-LAN. To allow wakeup from powered-down state S5, wakeup on PME (Power Management Event) is also required. The Intel adapter allows "Wake on Directed Packet", "Wake on Magic Packet", "Wake on Magic Packet from power off state", and "Wake on Link". Wake on Directed Packet is particularly useful as the machine will automatically come out of standby or hibernation when it is referenced, without the user or application needing to explicitly send a magic packet. Unfortunately in many networks waking on directed packet (any packet with the adapter's MAC address or IP address) or on link is likely to cause wakeup immediately after going to a low-power state. Details for any particular motherboard and network adapter are to be found in the relevant manuals; there is no general method. Knowledge of signals on the network may also be needed to prevent spurious wakening.
Some machines do not support Wake-on-LAN after they have been disconnected from power (e.g., when power is restored after a power failure). Use of an uninterruptible power supply
(UPS) will give protection against a short period without power, although the battery will discharge during a prolonged power cut.
Other problems can affect the ability to start or control the machine remotely: hardware failure of the machine or network, failure of the BIOS
settings battery (the machine will halt when started before the network connection is made, displaying an error message and requiring a keypress), loss of control of the machine due to software problems (machine hang, termination of remote control or networking software, etc.), and virus infection or hard disk corruption. Therefore, the use of a reliable server-class machine with RAID
drives, redundant power supplies, etc., will help to maximize availability. 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.
For a machine not in constant use, energy can be conserved by putting the machine into low-power RAM standby after a short timeout period. 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.
(VPN), which makes the remote computer appear to be a member of the Local Area Network
(LAN). In the absence of a VPN, a computer connected to a router can be woken if a magic packet sent over the Internet is routed to it. This requires any firewall to be set up to allow entry of the Wake-on-LAN signal to a specified port. The port can be forwarded to the computer to be woken up; or some routers permit the packet to be broadcast to the entire LAN. However, some routers do not support this as they will not forward broadcast packets.
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
computer networking standard that allows a computer to be turned on or woken up
Power management
Power management is a feature of some electrical appliances, especially copiers, computers and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state when inactive. In computing this is known as PC power management and is built...
by a network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
message.
The message is usually sent by a program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
executed on another computer on the same local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
. It is also possible to initiate the message from another network by using Subnet directed broadcasts or a WOL gateway service. Equivalent terms include Wake On WAN, Remote Wake-up, Power On By LAN, Power Up By LAN, Resume by LAN, Resume on LAN, Wake Up On LAN. In case the computer being woken is communicating via Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
, a supplementary standard called Wake on Wireless LAN (WoWLAN) must be employed.
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
Sleep Proxy Service
Apple's Bonjour Sleep Proxy service is an open sourcecomponent of zero configuration networking, designed to assist in reducing power consumption of networked electronic devices. A device acting as a sleep proxy server will respond to Multicast DNS queries for another, compatible device which has...
) feature.
History
In October of 1996, Intel and IBMIBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
formed the Advanced Manageability Alliance(AMA). In April of 1997, this alliance introduced the Wake on LAN technology.
The term "Wake on LAN" is a trademark of IBM Corporation.
Principle of operation
Wake-on-LAN is implemented using a special network message called a magic packet. The magic packet contains the MAC addressMAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
of the destination computer. The listening computer waits for a magic packet addressed to it and then initiates system wake-up.
The magic packet is sent on the data link or layer 2 in the OSI model
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
and broadcast to all NICs
Network card
A network interface controller is a computer hardware component that connects a computer to a computer network....
using the network broadcast address
Broadcast address
A broadcast address is a logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams...
; the IP-address (layer 3 in the OSI model) is not used.
It is a common misconception that because Wake-on-LAN is built upon broadcast technology it can only be used within the current network subnet. While this is generally the case there are some exceptions.
In order for Wake-on-LAN to work, parts of the network interface need to stay on. This consumes standby power
Standby power
Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity , refers to the electric power consumed by electronic and electrical appliances while they are switched off Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity...
, much less than normal operating power. If Wake-on-LAN is not needed, disabling it may reduce power consumption slightly while the computer is switched off but still plugged in.
Magic packet
The magic packet is a broadcast frameData frame
In computer networking and telecommunication, a frame is a digital data transmission unit or data packet that includes frame synchronization, i.e. a sequence of bits or symbols making it possible for the receiver to detect the beginning and end of the packet in the stream of symbols or bits...
containing anywhere within its payload 6 bytes of all 255 (FF FF FF FF FF FF in hexadecimal
Hexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
), followed by sixteen repetitions of the target computer's 48-bit MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
, for a total of 102 bytes.
Since the magic packet is only scanned for the string above, and not actually parsed by a full protocol stack, it may be sent as any network- and transport-layer protocol, although it is typically sent as a UDP
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
datagram
Datagram
A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....
to port
TCP and UDP port
In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication...
7 or 9, or directly over Ethernet as EtherType
EtherType
EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the PayLoad of an Ethernet Frame. This field was first defined by the Ethernet II framing networking standard, and later adapted for the IEEE 802.3 Ethernet networking standard.EtherType...
0x0842
A standard magic packet has the following basic limitations:
- Requires destination computer MAC address (also may require a SecureOn password)
- Does not provide a delivery confirmation
- May not work outside of the local network
- Requires hardware support of Wake-On-LAN on destination computer
The Wake-on-LAN implementation is designed to be very simple and to be quickly processed by the circuitry present on the network interface card (NIC) with minimal power requirement. Because Wake-on-LAN operates below the IP protocol layer the MAC address is required and makes IP addresses and DNS names meaningless.
Subnet directed broadcasts
A principal limitation of standard broadcast Wake-On-LAN is that broadcast packets are generally not routed. This prevents the technique being used in larger networks or over the internet. Subnet Directed Broadcasts (SDB) may be used to overcome this limitation. SDB may require changes to intermediate router configuration. Subnet directed broadcasts are treated as normal network packets until processed by the final (local) router. This router converts the packet into a true broadcast packet. This technique allows a broadcast to be initiated on a remote network but requires all intervening routers to forward the SDB. When preparing a network to forward SDB packets, care must be taken to filter such that only desired (e.g. WoL) SDB packets are permitted—otherwise the network becomes a participant in DDoS attacks such as the Smurf AttackSmurf attack
The Smurf attack is a way of generating significant computer network traffic on a victim network. This is a type of denial-of-service attack that floods a target system via spoofed broadcast ping messages....
.
Troubleshooting magic packets
Wake-on-LAN can be a frustrating technology to implement. This is because it requires appropriate BIOS, network card and, sometimes, operating system and router support to function reliably. In some cases hardware may wake from one low power state but not from others. This means that due to hardware issues the computer may be waking up from the "fully off state" (S5) but doesn't wake from sleep or hibernation or vice-versa. Also, it is not always clear what kind of magic packet a NIC expects to see.In that case, software tools like a packet analyzer can help with Wake-on-LAN troubleshooting as they allow to confirm (while the PC is still on) that the magic packet is indeed seen by a particular computer's NIC. The same magic packet can then be used to find out if the computer powers up from an offline state. This allows networking issues to be isolated from other hardware issues. In some cases they also confirm that the packet was destined for a specific PC or sent to a broadcast address
Broadcast address
A broadcast address is a logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams...
and they can additionally show the packet's internals.
In Windows Vista and higher, you can also determine how the OS was powered up. You can use powercfg /lastwake in the CMD prompt and it will list the "Wake Source". The Wake-on-LAN event should also be logged in the System event log.
Unauthorized access
Magic packets are sent via the data link or OSI-2 layerData link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
, which can be used or abused by anyone on the same LAN, unless the L2 LAN equipment is capable of (and configured for) filtering such traffic to match site-wide security requirements.
Firewalls may be used to prevent clients among the public WAN
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
from accessing the broadcast addresses of inside LAN segments, or routers may be configured to ignore subnet-directed broadcasts (see above.)
Certain NICs
Network card
A network interface controller is a computer hardware component that connects a computer to a computer network....
support a security feature called "SecureOn". It allows users to store within the NIC
Network card
A network interface controller is a computer hardware component that connects a computer to a computer network....
a hexadecimal password of 6 bytes. Clients have to append this password to the magic packet. The NIC
Network card
A network interface controller is a computer hardware component that connects a computer to a computer network....
wakes the system only if the MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
and password are correct. This security measure significantly decreases the risk of successful brute force attack
Brute force attack
In cryptography, a brute-force attack, or exhaustive key search, is a strategy that can, in theory, be used against any encrypted data. Such an attack might be utilized when it is not possible to take advantage of other weaknesses in an encryption system that would make the task easier...
s, by increasing the search space by 48 bits (6 bytes), up to 296 combinations if the MAC address is entirely unknown. However any network eavesdropping will expose the cleartext password.
Still, only a few NIC
Network card
A network interface controller is a computer hardware component that connects a computer to a computer network....
and router manufacturers support such security features.
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.
Interactions with network access control
The use of Wake-on-LAN technology on enterprise networks can sometimes conflict with network access control solutions such as 802.1x or 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. Configuration of these two features in tandem often requires tuning of timing parameters and thorough testing.Data privacy
Some PCs include technology built into the chipsetChipset
A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
to improve security for Wake-on-LAN. For example, Intel AMT
Intel Active Management Technology
Intel Active Management Technology is hardware-based technology for remotely managing and securing PCs out-of-band.Currently, Intel AMT is available in desktop PCs with Intel Core 2 processor with Intel vPro technology and available in laptop PCs with Centrino or Centrino 2 platform with vPro...
(a component of Intel vPro
Intel vPro
Intel vPro technology is computer hardware technology to allow remote access to the PC independent of the state of the operating system or power state of the PC. It consists of a set of features built into a PC's motherboard and other hardware...
technology), includes Transport Layer Security
Transport Layer Security
Transport Layer Security and its predecessor, Secure Sockets Layer , are cryptographic protocols that provide communication security over the Internet...
(TLS), an industry-standard protocol that strengthens encryption
Encryption
In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
.
AMT uses TLS encryption to secure an out-of-band
Out-of-band management
In computing, out-of-band management involves the use of a dedicated management channel for device maintenance...
communication tunnel to an AMT-based PC for remote management commands such as Wake-on-LAN. AMT secures the communication tunnel Advanced Encryption Standard
Advanced Encryption Standard
Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...
(AES) 128-bit encryption and RSA keys
Key (cryptography)
In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...
with modulus lengths of 2,048 bits. 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). Since the encrypted communication occurs “below” the OS level, it is less vulnerable to attacks by viruses, worms, and other threats that typically target the OS level.
IT shops using Wake-on-LAN through the Intel AMT implementation can wake an AMT PC over network environments that require TLS-based security, such as IEEE 802.1x
IEEE 802.1X
IEEE 802.1X is an IEEE Standard for port-based Network Access Control . It is part of the IEEE 802.1 group of networking protocols. It provides an authentication mechanism to devices wishing to attach to a LAN or WLAN....
, Cisco
Cisco
Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...
Self Defending Network
Network Access Control
Network Access Control is an approach to computer network security that attempts to unify endpoint security technology , user or system authentication and network security enforcement.-Background:Network Access Control is a computer networking solution that uses a set of protocols to define and...
(SDN), and Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
Network Access Protection
Network Access Protection
Network Access Protection is a Microsoft technology for controlling network access of a computer host based on the system health of the host, first introduced in Windows Server 2008....
(NAP) environments. The Intel implementation also works for wireless
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
networks.
Hardware requirements
Wake-on-LAN support is implemented on the motherboardMotherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
(BIOS) of a computer and the network interface (firmware), and is consequently not dependent on the operating system (and NIC drivers) running on the hardware. Some operating systems can control Wake-on-LAN behaviour via hardware drivers. If the network interface is a plug-in card rather than being integrated into the motherboard, the card may need to be connected to the motherboard by an additional cable. Motherboards with an embedded Ethernet controller which supports Wake-on-LAN do not need a cable. The power supply must meet ATX
ATX
ATX is a motherboard form factor specification developed by Intel in 1995 to improve on previous de facto standards like the AT form factor. It was the first big change in computer case, motherboard, and power supply design in many years, improving standardization and interchangeability of parts...
2.01 specifications.
Hardware implementations
Older motherboards must have a WAKEUP-LINK header onboard connected to the network cardNetwork card
A network interface controller is a computer hardware component that connects a computer to a computer network....
via a special 3-pin cable; however, systems supporting the PCI 2.2 standard and with a PCI 2.2 compliant network adapter card do not usually require a Wake-on-LAN cable as the required standby power is relayed through the PCI bus.
PCI version 2.2 supports PME (Power Management Events). PCI cards send and receive PME signals via the PCI socket directly, without the need for a Wake-on-LAN cable.
Wake-on-LAN usually needs to be enabled in the Power Management section of a PC motherboard's BIOS setup utility, although on some systems, such as Apple computers, it is enabled by default. On older systems the bios setting may be referred to as "WOL", on newer systems supporting PCI version 2.2, it may be referred to as "PME" (Power Management Events, which include WOL). It may also be necessary to configure the computer to reserve standby power for the network card when the system is shut down.
In addition, in order to get Wake-on-LAN to work it is sometimes required to enable this feature on the network interface card or on-board silicon. Details of how to do this depend upon the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
and the device driver.
Laptops powered by the Intel Centrino Processor Technology or newer (with explicit BIOS support) allow waking up the machine using wireless Wake on Wireless LAN (WoWLAN).
In most modern PCs, ACPI
ACPI
ACPI may refer to:*Advanced Configuration and Power Interface for computer configuration and management*Animation Council of the Philippines, Inc....
is notified of the "waking up" and take control of the Power up. In ACPI, OSPM must record the "wake source" or the device that is causing the power-up. The device being the "Soft" power switch, the NIC (via Wake-on-LAN), the cover being opened, a temperature change, etc.
The 3-pin WOL interface on the motherboard consist of pin-1 +5V DC (red), pin-2 Ground (black), pin-3 (green or yellow). By supplying +5V DC to the pin-3 wake signal with +5V DC the computer will be triggered to power up provided WOL is enabled in the BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
configuration.
Software requirements
Software which sends a WoL magic packet is referred to in different circles as both a "client" and a "server", which can be a source of confusion. While WoL hardware/firmware is arguably performing the role of a "server", web based interfaces which act as a gateway through which users can issue WoL packets without downloading a local client often become known as "The Wake On LAN Server" to users. Additionally, software that administers WoL capabilities from the host OS side may be carelessly referred to as a "client" on occasion, and of course, machines running WoL generally tend to be end-user desktops, and as such, are "clients" in modern IT parlance.Sending the magic packet
Software to send WoL magic packets is available for all modern platforms, including Windows, Macintosh and Linux, plus many smart phones. Also there are web sites on the Internet that allow a magic packet to be sent online without charge. Example source codeSource code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
for a developer to add Wake-on-LAN to a program is readily available in many computer languages.
Some home routers are able to send magic packets to LAN, for example routers with the DD-WRT
DD-WRT
DD-WRT is a Linux-based firmware for several wireless routers, most notably the Linksys WRT54G . Like other similar projects, DD-WRT is third-party firmware designed to replace the firmware that ships pre-installed on many commercial routers...
or Tomato
Tomato Firmware
Tomato Firmware is a partially free HyperWRT-based, Linux core firmware distribution for a range of Broadcom chipset based wireless routers, most notably the older-model Linksys WRT54G , Buffalo AirStation, Asus Routers and Netgear's WNR3500L...
firmware have a built-in Wake On Lan client. The 3rd party FOSS project OpenWrt
OpenWrt
OpenWrt is a Linux distribution primarily targeted at routing on embedded devices. It comprises a set of about 2000 software packages, installed and uninstalled via the opkg package management system. OpenWrt can be configured using the command-line interface of BusyBox ash, or the web interface...
supports both Linux implementations for WoL etherwake and wol.
Receiving the magic packet
Most WoL hardware may be configured directly using the system BIOS. However, it is often more desirable to configure the functionality without interrupting the normal operations of the machine. The BIOS step is necessary in addition to configuration from the OS in some cases.Microsoft Windows
Modern versions of Microsoft Windows integrate WoL functionality into the Device Manager. This is available in the Power Management tab of each network device. In most cases correct BIOS configuration is also required for WoL to function.Mac hardware (OS X)
Modern Mac hardware features integrated WoL functionality, controlled via the OS X System Preferences Energy Saver panel, in the Options tab. Marking the Wake for Ethernet network administrator access checkbox enables Wake-on-LAN.
Apple's Apple Remote Desktop
Apple Remote Desktop
Apple Remote Desktop is a Macintosh application produced by Apple Inc., first released on March 14, 2002, that replaced a similar product called Apple Network Assistant...
client management system can be used to send Wake-on-LAN packets, but there are also freeware and shareware Mac OS X applications available.
On Mac OS X Snow Leopard, the service is called Wake On Demand or Bonjour Sleep Proxy and is synonymous with the Sleep Proxy Service
Sleep Proxy Service
Apple's Bonjour Sleep Proxy service is an open sourcecomponent of zero configuration networking, designed to assist in reducing power consumption of networked electronic devices. A device acting as a sleep proxy server will respond to Multicast DNS queries for another, compatible device which has...
. It comes enabled out of the box, but for previous versions of the operating system, the service will need to be enabled under the Energy Saver pane of System Preferences
System Preferences
System Preferences is an application included with the Mac OS X operating system that allows users to modify various system settings which are divided into separate preference panes...
. Your network interface card may allow the service to function only on WiFi, only on Ethernet, or both.
Other machine states and LAN wakeup signals
In the early days of Wake-on-LAN the situation was relatively simple: a machine was connected to power but switched off, and it was arranged that a special packet be sent to switch the machine on.Since then many options have been added and standards agreed upon. A machine can be in 7 power states from S0 (fully on) through S5 (powered down but plugged in) and disconnected from power (G3, Mechanical Off), with names such as "sleep", "standby", and "hibernate". In some reduced-power modes the system state is stored in RAM and the machine can wake up very quickly; in others the state is saved to disk and the motherboard powered down, taking at least several seconds to awake. The machine can be woken from a reduced-power state by a variety of signals.
The machine's BIOS must be set to allow Wake-on-LAN. To allow wakeup from powered-down state S5, wakeup on PME (Power Management Event) is also required. The Intel adapter allows "Wake on Directed Packet", "Wake on Magic Packet", "Wake on Magic Packet from power off state", and "Wake on Link". Wake on Directed Packet is particularly useful as the machine will automatically come out of standby or hibernation when it is referenced, without the user or application needing to explicitly send a magic packet. Unfortunately in many networks waking on directed packet (any packet with the adapter's MAC address or IP address) or on link is likely to cause wakeup immediately after going to a low-power state. Details for any particular motherboard and network adapter are to be found in the relevant manuals; there is no general method. Knowledge of signals on the network may also be needed to prevent spurious wakening.
Unattended operation
For a machine which is normally unattended precautions need to be taken to make the Wake-on-LAN function as reliable as possible. For a machine procured to work in this way, Wake-on-LAN functionality is an important part of the purchase procedure.Some machines do not support Wake-on-LAN after they have been disconnected from power (e.g., when power is restored after a power failure). Use of an uninterruptible power supply
Uninterruptible power supply
An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
(UPS) will give protection against a short period without power, although the battery will discharge during a prolonged power cut.
Awakening without operator presence
If a machine that is not designed to support Wake-on-LAN is left powered down after power failure, it may be possible to set the BIOS to start it up automatically on restoration of power, so that it is never left in an unresponsive state. A typical BIOS setting is AC back function which may be on, off, or memory. On is the correct setting in this case; memory, which restores the machine to the state it was in when power was lost, may leave a machine which was hibernating in an unwakeable state.Other problems can affect the ability to start or control the machine remotely: hardware failure of the machine or network, failure of the BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
settings battery (the machine will halt when started before the network connection is made, displaying an error message and requiring a keypress), loss of control of the machine due to software problems (machine hang, termination of remote control or networking software, etc.), and virus infection or hard disk corruption. Therefore, the use of a reliable server-class machine with RAID
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
drives, redundant power supplies, etc., will help to maximize availability. 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.
For a machine not in constant use, energy can be conserved by putting the machine into low-power RAM standby after a short timeout period. 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.
Wake on Internet
The computer being woken does not know whether the wakeup signal comes from another machine on the same network or from anywhere else. If the magic packet can be made to reach a computer, it can originate anywhere (e.g., from the Internet). This can be achieved by a Virtual Private NetworkVirtual private network
A virtual private network is a network that uses primarily public telecommunication infrastructure, such as the Internet, to provide remote offices or traveling users access to a central organizational network....
(VPN), which makes the remote computer appear to be a member of the Local Area Network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
(LAN). In the absence of a VPN, a computer connected to a router can be woken if a magic packet sent over the Internet is routed to it. This requires any firewall to be set up to allow entry of the Wake-on-LAN signal to a specified port. The port can be forwarded to the computer to be woken up; or some routers permit the packet to be broadcast to the entire LAN. However, some routers do not support this as they will not forward broadcast packets.
See also
- Alert on LANAlert on LANAlert on LAN is a 1998, IBM- and Intel-developed technology that allows for remote management and control of networked PCs. AOL requires a Wake on LAN adapter.- Technical details :...
- Alert Standard FormatAlert Standard FormatAlert Standard Format is a DMTF standard for remote monitoring, management and control of computer systems in both OS-present and OS-absent environments...
- Desktop and mobile Architecture for System HardwareDesktop and mobile Architecture for System HardwareDASH is a DMTF standard on requirements for implementing the Desktop and Mobile Architecture for System Hardware....
- Intel vProIntel vProIntel vPro technology is computer hardware technology to allow remote access to the PC independent of the state of the operating system or power state of the PC. It consists of a set of features built into a PC's motherboard and other hardware...
- RTC AlarmRTC AlarmA real time clock alarm is a feature that can be used to allow a computer to 'wake up' after shut down to execute tasks every day or on a certain day. It can sometimes be found in the 'Power Management' section of a motherboard's BIOS setup. However, newer BIOS setups do not include an RTC alarm...
- Sleep Proxy ServiceSleep Proxy ServiceApple's Bonjour Sleep Proxy service is an open sourcecomponent of zero configuration networking, designed to assist in reducing power consumption of networked electronic devices. A device acting as a sleep proxy server will respond to Multicast DNS queries for another, compatible device which has...
- Wake-on-RingWake-on-ringWake-on-Ring , sometimes referred to as Wake-on-Modem , is a specification that allows supported computers and devices to "wake up" or turn on from a sleeping, hibernating or "soft off" state Wake-on-Ring (WOR), sometimes referred to as Wake-on-Modem (WOM), is a specification that allows supported...
- Telephone line ring event - Conventional PCI pinout - Power Management Event (PME#) signal
- ATXATXATX is a motherboard form factor specification developed by Intel in 1995 to improve on previous de facto standards like the AT form factor. It was the first big change in computer case, motherboard, and power supply design in many years, improving standardization and interchangeability of parts...
- Motherboard standard that provides for power management - Wired for ManagementWired for ManagementWired for Management was a primarily hardware-based system allowing a newly built computer without any software to be manipulated by a master computer that could access the hard disk of the new PC to paste the install program. It could also be used to update software and monitor system status...
External links
- Troubleshooting Remote Wake-up Issues Useful WOL troubleshooting information from Intel
- AMD's Magic Packet Technology white paper Publication# 20213
- Wake-on-LAN History and How-To Guide
- Wake-on-LAN Security Best Practices (Microsoft, 2008)
- Wake On Local Area Network (LAN) WOL guide for Microsoft Windows from Energy Star (EPA)