You can find more info on WOL on Wikipedia. BTW, I will use UDP port 9 in the examples. Usually the magic packet is an UDP packet with destination port 0, 7 or 9, but this is not mandatory. When the powered off device’s ethernet card detects this special frame, it powers up the device. What does it make this packet magic? The fact that it must contain the Mac Address of the device to be woken up, repeated 16 times. This broadcast frame is processed by all the hosts on the lan segment. WOL is usually done by generating a packet with destination IP address the broadcast address of the network (in a common 192.168.0.0/24 network, it is directed to 192.168.0.255 or 255.255.255.255), which produces an ethernet frame with FF:FF:FF:FF:FF:FF destination mac address. Some network devices and PCs can listen for incoming special packets on their ethernet interfaces even when shutdown, and this is used to allow them to be powered up with a special magic packet, which is used by Wake-On-Lan (from now WOL).
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