After upgrading my Mac mini from Leopard to Snow Leopard it did no longer wake from sleep when I sent the magic wake-on-lan package. So, I checked the network and energy settings and noticed that Snow Leopard’s new Wake-On-Demand (WOD ?) feature was disabled. I didn’t change that and started to wonder why WOL didn’t work.
Internet search lead to http://support.apple.com/kb/HT3774 in which Apple explains that “for some earlier Macs this option must be enabled [manually]”. What I didn’t immediately grasp is that WOD is a full replacement for WOL. I was initially reluctant to enable this option because I don’t want WOD (don’t have the necessary AirPort Extreme anyway) but only WOL. However, even after going through the article this didn’t become apparent. One must guess or assume…
What further clarified the situation was an ars technica article about “The sleeping Mac dilemma”.
So, to cut a long story short. Snow Leopard’s WOD falls back to WOL mode if it can’t find the necessary infrastructure (AirPort Extreme or Time Capsule) and therefore you need to enable WOD if you want WOL. Logical, isn’t it?