Booting for Lazy People – Wake On LAN
Gepost op 2007.08.23 | Reacties (4) | Technologie
Wake Up!
Not you… The computer!
Just had some fun enabling Wake On LAN on one of my computers. A great technology for the lazy people among us, you simply sit in your chair and realize you need to access some other computer in your house, but sadly enough it isn’t powered on. The fit among us might simply walk to the machine and boot it, but I’d rather open up some program, hit a button and with some magic the machine starts up. Funnily enough, the keyword behind all of this is appropriately named a ‘Magic Packet‘, waking up the dead from their sleep.
This Magic Packet is nothing more than an UDP packet being broadcast with the MAC address of the computer to power on. I don’t know if it has a technical reason or is more meant as a joke to go with the naming, but the MAC address is contained 16 times in the packet, just as the hexadecimal numeral system is base 16.
To set this up, I had to go into the BIOS and enable the Wake On LAN features. This seems to be the most annoying part of the while thing, since I’ve already found one BIOS which didn’t list any options for it.
The only thing left is some configuration in Windows, telling the network card is should enable its Wake On LAN features and explaining to Windows that the network card is allowed to wake the computer. (Picture taken on another computer than the one I configured however, since it was running a Dutch version of Windows)
That’s the only configuration needed, now we need to use an application which can send these Magic Packets, AMD’s PCnet Magic Packet Utility being one of them.
From now on I can boot machines from my desk, log in remotely and shut them down from a distance as well, just a little bit more and my life will revolve around my desk!
you would need to know the MAC address for all the PCs you want to wake up.
You can probably get it from the router’s configuration table though.
Hi David,
You might be interested in my Wake on LAN for C# sample too at http://community.bartdesmet.net/blogs/bart/archive/2006/04/02/3858.aspx. It’s part of a larger Terminal Services thin client solution that tracks the MAC addresses of the thin client machines in the network and allows WOL and remote shutdown by the IT admin or on a server-scheduled basis, e.g. in a school environment.
To coolpran: ping the computer and check your computer’s arp cache using arp -a to reveal the MAC address of the target computer.
-Bart
Almost forgot what I wanted to clarify: the Magic Packet format. The first 6 FF values are for sync purposes, and act as the initial state to the receiving adapter’s Magic Packet detector state machine. Next, incoming bytes are checked against the MAC address which is stored in the Ethernet card’s ROM. To reduce the chance of having some packet arriving at the adapter that matches 6xFF and the MAC address once – which would wake up the computer mistakenly – repetition of the MAC address is required. A four bit counter is commonly available, so adding that to the Ethernet card’s design isn’t too difficult (e.g. in CMOS), hence the ‘logical choice’ for 16 (if you can count up to 16, why would you just use part of that capacity?).
Hope this can clarify things a bit, for what it’s worth – as long as the pc wakes up, we’re more than happy, aren’t we?
You can try this website for waking up your Wake-on-Lan enabled PC from the Internet:
http://wol.vanis.cz