[SLUG] Wake on Lan

[Mike Bennett]

On 2/26/07, Stephen O'Neill <soneill84 at yahoo.co.uk> wrote:
> To elaborate a tiny bit on what Mike says, to help with your internet
> searches, passing a WOL packet to the internal network is known as
> "broadcasting". With NAT routers which I have come across you need to
> setup firewall rules to pass packets to a specific IP address (e.g.
> 192.168.0.2) - it is not possible to use a broadcast address (e.g.
> 192.168.0.255).


Some routers will allow you to pass a MAC address with the command to
broadcast a packet and therefore direct the external packet to the
appropriate internal machines. The router, if it supports remote WoL,
should transform the incoming request into a broadcast to be sent over
the internal network anyway, because there will be no internal IP
address to pass the data to if the computer is powered down.

WoL packets break down into an initial data "wake-up" call or "magic
packet". This is normally just a burst of solid data to alert all
machines with WoL activated to listen out for the next bit.
The second part of a WoL is the broadcasting of the MAC address of the
target machine to wake up. This is normally repeated 8 or 16 times and
on some systems is then followed by  a termination packet (although
this is not required).

All machines in broadcast range of the originator will then check the
MAC address against the MAC address of the NIC recieving the data. If
it matches, then the machine will be booted.

Therefore it is not possible, as far as I am aware, to do it without a
router supporting WoL as you will have to pass the MAC address of the
target machine to the router.

The other option for this is to have an internal machine that is
always on and can do the same work as the router, therefore you can
use the same method (of broadcasting to the target MAC) from an
internal machine, and don't have to have a router that supports WoL as
you can just get or write a server/client to pass the data through to
the designated "always-on" internal machine as a standard protocol
over TCP/IP.

Hope this is helpful.

Cheers,
Mike