The MagicPacket: How WoL Works
WoL-enabled computers essentially wait for a "magic packet" to arrive that includes the NIC's MAC address in it. These magic packets are sent out by professional software made for any platform, but can also be sent by routers and internet-based websites. The typical ports used for WoL magic packets are UDP 7 and 9 . Because your computer is actively listening for a packet, some power is feeding your network card which will result in your laptop's battery draining faster, so road warriors should take care to turn this off when you need to eke out some extra juice.
Magic packets are usually sent over the entirety of a network and contain the subnet information, network broadcast address, and the MAC address of the target computer's network card, whether Ethernet or wireless. The above image shows the results of a packet sniffer tool used on magic packet.