Exactly this. Many modern PHYs also integrate 802.3az (energy-efficient ethernet, a subset of Green Ethernet) but it's not super common.

I also finally found this old page of using an old dev board to construct a WoL listener for a mobo that didn't support it -- might be an interesting read for the curious: https://web.archive.org/web/20140525022112/https://hackingbe...

> In this script a fifo is created where the output of tcpdump is dumped. For whatever reason tcpdum | grep was not working properly, and would have a “miss” rate of about 50%. So tcpdump output is dumped in the fifo:

>

> tcpdump -i eth1 2>&1 | tee > /tmp/tcp_wol.fifo &

>

> and it’s grepped in a loop, when the magic packet (see http://en.wikipedia.org/wiki/Wake-on-LAN) is found , a led is triggered, thus powering-up the computer (with a driver and relay, will come back at this).

I have measured the powered off energy usage of my desktop computer at the wall, and it hovered about 5-6 W (resolution of the power meter was just whole watts). That would be split between losses in the PSU and WoL, and possibly other circuits. But I don't have any other such wakeups enabled (but that doesn't mean that the motherboard is designed super well to disable it fully if not needed). Turning off WoL made a difference of about 2 W (meter hovered around 3-4 W).

One thing I noticed is that if I connect to a gigabit upstream port, that the connection drops to 100 mbit/s when the computer is off, but if I connect to a 2.5 Gbit port, it stays at full speed. This is based both on LEDs on the connector as well as the OpenWRT dashboard on the router. If it made a difference it was too small to reliably measure with my simple meter.

If it makes a difference (potentially does for conversion losses I would guess), this is on 230 V mains.