Wake on LAN (was: Re: evolution in action (Re: Napster))

[Seb Wills]

On Fri, 6 Sep 2002, Roland Perry wrote:

> In message
> <BB3AF5C4A607FE4E969AA39CB42B6C7B112D7C@bond.campus.ncl.ac.uk>, Quentin
> Campbell <Q.G.Campbell@newcastle.ac.uk> writes
> >In some circumstances a laptop may provide LESS protection than a
> >desktop PC.
> >
> >Many (most?) laptops have the "Wake on LAN" feature. If that feature is
> >left "enabled" AND the latop is left connected to the network, a
> >shut-down laptop will power-up and re-boot itself
>
> What if a boot-up password is set? Do you really mean boot-up, anyway,
> as my notebook takes well over any normal IP timeout to boot!

I'm not sure about laptops, but all modern desktops have Wake-on-LAN
support if the network card supports it. The PC really can wake up from
the "fully off" state (i.e. as off as you can make it without switching it
off at the wall). It will then boot up normally (or resume if it was
suspended). So a boot password should stop it, as will making sure the
Wake-on-LAN feature is disabled in BIOS. IP timeout is irrelevant since
the Wake on LAN packet just wakes the machine - no reply is generated.

> >when it detects any
> >network activity (assuming that the battery is charged).
>
> *Any* network activity?

No. The network card has to receive a special Wake-on-LAN packet via an
ethernet broadcast packet. The machine wakes up if the payload of that
magic packet contains the machine's MAC address. Some network cards also
require a simple "password" to be included in the packet too.

One implication is that the person trying to wake up the PC needs to be
able to send a broadcast packet which will reach the target machine. Which
usually means they have to be acting from a machine on the same subnet.

seb