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Remote Wake-Up refers to remotely turning on a networked computer by sending a network message (called a magic packet) that contains the MAC address of the computer. On receipt, the computer initiates the system wake-up. The computer receiving the magic packet does not need to be left “on,” as was the case before Remote Wake-Up became available; so IP personnel no longer have to manually turn “on” networked computers, or remind employees to do so, before remotely checking, configuring, installing software or other tasks. This feature is included in Intel’s Wired for Management (WfM) network specification.
Generally, Remote Wake-Up will only work if magic packets are sent from a computer on the same local area network (LAN) or within the current network subnet. However, there are exceptions making it possible to remotely wake-up a computer from outside its LAN.
The Remote Wake-Up feature goes by many names, including: wake on LAN (WOL), wake on WAN, wake up on LAN, power On By LAN, power Up By LAN, resume by LAN and resume on LAN.
For computers communicating via WiFi, the wake on wireless LAN” (WoWLAN) supplementary standard must be used.
Remote Wake-Up is independent of the operating system, or network interface card (NIC), used by the computer. Support for this feature is implemented on the motherboard (in the BIOS) along with the network interface or firmware. However, some operating systems can control the operation with hardware drivers.
The magic packets use the data link layer in the OSI model as they are sent to all NICs using the network broadcast address. The magic packet does not provide any delivery confirmation signal back to the sending computer.
For Remote Wake-Up to function, there are parts of the network/computer interface that need to remain powered, even though the computer is shut off; and some power is consumed for this purpose, as long as the computer is plugged in to a powered electrical outlet.
To function reliably, Remote Wake-Up requires the proper BIOS and NIC; and sometimes the proper OS and support for the final router are required. This can make the setup and testing frustrating for the IT network technician. Moreover, different hardware have a variety of low-power states, such as a fully-off state, sleep or hibernation; some may allow wake-up while others may not.
Remote Wake-Up does have some security issues. Magic packets may be sent by anyone on the LAN, and in some cases by sources outside the LAN. Some measures can be taken to reduce the risk of unintended magic packets being received or others sent with malicious intent; these include: filtering data transmissions to match site-wide security requirements; firewalls preventing access to broadcast addresses within the LAN segments; and the use of 6 byte hexadecimal passwords which must be appended to each magic packet received.