Lately I came across a requirement for an ability to remotely turn on computers in our company. Couple of team members (including me...) tend to work from home sometimes so they leave their PCs running when they leave the office so the next day they could access it over Remote Desktop. Do you spot a problem already? To be honest I did not realise this was a problem either ... until an electricity bill came in. The workstation PCs are running nonstop (no one really bothers to switch them off, what if they did not go to the office tomorrow ...), which obviously has very negative impact on the electricity consumption in our office.

So it was clear we need to do something about it. One can switch off a PC using Remote Desktop very easily (you can do it directly from Start menu), but having ability to switch off a computer remotely is useless unless you can then remotely switch on the computer again. And that is where Wake on LAN finds its place.

"Magic Packet"

Wake On LAN (sometimes referred as WOL or WoL) is a marketing term used for ability to bring computer out of Stand-By mode by sending it a special packet, called "Magic Packet".

When you shutdown Windows, all modern ATX-power based PCs do not switch off completely. Instead they enter a Stand-By mode, which means RAM, CPU and hard drives are switched off, but motherboard itself and a network card are still powered. To determine if your network card supports WOL, shut down your PC and check the Link LED on the network card - if it is still active, your network card is still powered and should support Wake on LAN.

Even though a PC is shut down, the network card is listening on the data layer (usually Ethernet) level and scans incoming packets for special character sequence. If it detects the sequence, it will turn on the PC. This sequence, called Magic Packet, has following structure:

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