Wake Up On Lan

Recently I’ve wanted to remotely start up machines, either because a machine the other end of VPN is down or I can’t be bothered to walk upstairs and turn on a desktop file server whilst using a laptop! What started off as a simple process seemed to have a number of gotcha’s that I thought I’d record.
The basic premise is that if your machine has a network card that support Wake Up On Lan (WOL) then if you enable this setting you can…wake the machine up via the network. There seem to be various ways of doing this but I chose the "Magic Number" approach using a utility called MC-WOL.EXE.
The basic steps in using this little program are:
  1. You first need to discover the MAC address of the network card in question. To do this I ran a command window on the target machine and entered "IPCONFIG /ALL". Note down the address of the card, it’s not the IP address but a series of hex numbers normally "-" separated.
  2. Ensure the machine’s BIOS is configured to accept WOL. This usually requires rebooting your machine and going into the "setup" for the BIOS. Locate your network settings and ensure that WOL is enabled. Note that on some systems you can have conflicting settings. So Wake Up from Hibernation settings often conflict, see you BIOS/Motherboard settings for more details.
  3. Switch your machine off and run MC-WOL from another machine.

This should work, however there are a number of gotcha’s.

  1. Firewalls. I only use this via a LAN or VPN so I’ve not had this problem but for sensible reasons a firewall can get in the way of your call. This is good news since you don’t want people on the internet starting your machines up.
  2. "Soft" and "Hard" shutdowns. This was the first time I’d come across this concept. You can shut a machine down in two different ways. For example, pressing Shutdown in Windows produces a Soft shutdown and the machine can normally be woken up. Hold the power button and switching the machine off results in a Hard shutdown and it won’t wake up. This is annoying since the reason you want to wake a machine might be because someone’s turned it off or ’cause of power cut, et al.
  3. Operating System settings. The BIOS changes aren’t always enough. Sometimes you have to go into Hardware Manager, select the network card and look at its settings. My cards have "Use Magic Number" or "Enable WOL". As you see there doesn’t seem to be a standard so look for something that sounds like Wake Up…not great instructions but there you go.

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