IT Technology: Magic Packet

The magic packet is a broadcast frame 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.[6]

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
• 802.11 wireless interfaces do not maintain a link in low power states and cannot receive a magic packet

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 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.


Reference:
Wake-on-LAN
http://en.wikipedia.org/wiki/Wake-on-LAN