[CentOS] ether-wake

Mon May 18 08:59:12 UTC 2020
Pete Biggs <pete at biggs.org.uk>

On Sun, 2020-05-17 at 20:25 -0600, R C wrote:
> Ok,  I get that, found it before;  "typically sent as a UDP datagram to 
> port 0, 7 or 9, or directly over Ethernet as EtherType 0x0842"
> The keyword being 'typically',   but what is it that ether-wake actually 
> uses/does?  (I need to forward a WOL packet to a different
> vlan on some Cisco hardware, between two Centos machines).

WoL packets are not routeable/forwardable. They are Layer 2 broadcast
packets that contain the MAC address of the machine that needs to be
woken up. But since you quoted the Wikipedia article on WoL you would
know that and it specifically says what the magic packet is and does.

The format of the packet is unimportant, all that happens is that the
ethernet *card* receives the packet, sees that it's a magic WoL packet
for that card and turns on the hardware "wakeup" line to the machine. 

The packets need to be sent on the same network as the target computer
- we did it a while ago for a very large complex network and it needed
a box behind every single router that could be commanded to send out
the WoL packet for a specific MAC address. We eventually abandoned it.