WOL over the internet

A computer A is connected to the internet by means of an ADSL
modem/router, which is connected to A at A's Ethernet port.

Assuming that we know the Ethernet address of this board, and
that the hardware (motherboard, Ethernet board and BIOS configuration)
does support WOL, would it be possible to wake up A from some other
computer B in the internet? Would one have to open any specific ports in
A's router/modem for the wake up packet to reach A, or would any port?

Użytkownik H.K. Kingston-Smith napisał:
> A computer A is connected to the internet by means of an ADSL
> modem/router, which is connected to A at A's Ethernet port.
>
> Assuming that we know the Ethernet address of this board, and
> that the hardware (motherboard, Ethernet board and BIOS configuration)
> does support WOL, would it be possible to wake up A from some other
> computer B in the internet? Would one have to open any specific ports in
> A's router/modem for the wake up packet to reach A, or would any port?
>
>
>
AFAIK you need a router with WoL built-in. WoL works on layer-2 and your
connection to router (from Internet) is in Layer-3. So with "normal"
router there is no way to generate "magick" packet on LAN.

W.P.

On Thu, 28 Jun 2007 12:23:35 +0200, W.P. wrote:

> Użytkownik H.K. Kingston-Smith napisał:
>> A computer A is connected to the internet by means of an ADSL
>> modem/router, which is connected to A at A's Ethernet port.
>>
>> Assuming that we know the Ethernet address of this board, and
>> that the hardware (motherboard, Ethernet board and BIOS configuration)
>> does support WOL, would it be possible to wake up A from some other
>> computer B in the internet? Would one have to open any specific ports
>> in A's router/modem for the wake up packet to reach A, or would any
>> port?
>>
>>
>>
> AFAIK you need a router with WoL built-in. WoL works on layer-2 and your
> connection to router (from Internet) is in Layer-3. So with "normal"
> router there is no way to generate "magick" packet on LAN.

It can work, at least with some implementations:
http://forums.speedguide.net/showthread.php?t=141643

OP will need to set up a port forward on the router to 0, 7 or 9 UDP,
depending on the WOL implementation of the target machine.
http://en.wikipedia.org/wiki/Wake-on-LAN


Alternatively, with a Linksys WRT54G running third-party firmware (I use
Sveasoft Alchemy), it is possible to ssh into the router from the internet
and use the WOL utility on the router to send the magic packet to the LAN.



--


--
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On Thu, 28 Jun 2007, in the Usenet newsgroup comp.os.linux.networking, in
article <(E-Mail Removed)>, H.K. Kingston-Smith wrote:

>A computer A is connected to the internet by means of an ADSL
>modem/router, which is connected to A at A's Ethernet port.

You will have to look at that "modem/router" as that's where the
difficulty will lie.

> Assuming that we know the Ethernet address of this board, and
>that the hardware (motherboard, Ethernet board and BIOS configuration)
>does support WOL, would it be possible to wake up A from some other
>computer B in the internet?

Yes

>Would one have to open any specific ports in A's router/modem for the
>wake up packet to reach A, or would any port?

The "Wake-On-LAN" "magic packet" is merely specified as having the
target NIC adapters MAC address repeated 16 times in the data field.
Thus, the packet can be anything you can send - a ping is often
easiest to create, but any protocol that your network allows is
equally acceptable, such as TCP, UDP, IPX, Appletalk, what-ever.
Donald Becker used to have a program called "ether-wake" as part of
the "diag-ether" tarball.

THE PROBLEM is getting the router to deliver the packet. For _any_
data transmission on an Ethernet type of network, the local _sending_
station (in this case, the "modem/router") has to know the MAC address
to send it to. The packet must either be a broadcast (and the sending
station accepting/allowing this concept), OR the packet must be a normal
"unicast" directed at the MAC address of the destination host.[1] The
operating system remembers this data in an ARP cache (try "/sbin/arp -a"
to see the current MAC/IP relationships your system knows about). The
normal problem about the ARP cache is that Internet standards
(specifically RFC1122 Section 2.3.2.1) requires this data to expire in
a timely manner - the recommended value is "on the order of a minute".
So, a minute after the router stops talking to host $FOO, the ARP cache
entry should disappear. Thus, if some _local_ host wants to "talk" to
host $FOO, it either must have the MAC/IP entry in it's arp cache, OR it
sends an ARP request (a simple Ethernet broadcast) to try to get this
information.

12:38:06.114000 arp who-has 192.0.2.21 tell 192.0.2.133

The rub come from the fact that "192.0.2.21" is powered down, and won't
answer this ARP request. The result is that "192.0.2.133" can't talk to
"192.0.2.21" because it can't determine the MAC address to send packets
to.

WHAT TO DO? There are two ways around this problem. The first is to
send the WOL packet to the network broadcast address. This is a less
than optimal solution, as a LOT of routers are configured to not send
such packets (abuse prevention). The other solution is to use a
static arp entry on the local "sending" station. For a common Linux box,
see the arp(8) man page, and look at the "-s" option. Most routers have
a similar command/capability. NOTE: On a switched network (as opposed
to coax or using a hub), the network switch _may_ also require a static
entry - see the manual/documentation for your network switch.

Old guy

[1] On a non-switched network (coax or hub), the packet _can_ be sent
to any MAC address on the local wire. A switch would not forward this
packet to all hosts, thus the actual destination MAC address is needed.