Wake Up and Smell the Network

By Joseph Moran

June 15, 2007

More and more people want to take advantage of remote access, but your PC has to be on to be accessible, right? Well, yes and no, thanks to a technology called Wake on LAN.

In the ongoing discussion about the problem of climate change, much is made of our penchant for gas-guzzling vehicles. But another major culprit is our use of electricity — the desktop PCs found in a typical home or office can consume a lot of energy, especially if they're powered on 24/7.

Of course, you can curtail the amount of power a system uses by setting it to automatically go into standby or hibernate mode, or even by simply shutting it down during extended periods of disuse. You might also think that a disadvantage of doing this is that it precludes you from having remote access your system — after all, it has to be on to be accessible, right?

Well, yes and no, because a technology called Wake on LAN can let you bring your PC back to life no matter what power-saving mode it's in — even if it's completely turned off. In order to take advantage of Wake on LAN, your system's BIOS, Ethernet adapter and network drivers must all support the feature, but as long as your system is less than about five years old, it should be compatible.

(Note that the steps outlined below assume that you're using a system running Windows XP with a wired Ethernet connection — it doesn't work with Wi-Fi adapters — and that you're also using a broadband router.)

System Prep
Start by rebooting your system and entering its BIOS setup screen by hitting the F2 or DEL key (depending on your system) before Windows starts to load. Look for a setting labeled Wake on LAN, Power on LAN, or something similar, and make sure it's enabled. (Most systems BIOS have numerous configuration pages, so you may find the Wake on LAN settings buried under a Power Management or ACPI heading.) Be sure to save your BIOS changes, then reboot the system.

The next step is to make sure that Wake on LAN is enabled on your Ethernet adapter. Open up Device Manager, find the entry for your adapter, and double-click it. Then click the Advanced tab, look for any settings that begin with "Wake on," and set them all to Enable. Now click the Power Management tab, and make sure there are check marks next to any option to Allow the computer to turn off this device to save power, Allow this device to bring the computer out of standby, and Only allow management stations to bring the computer out of standby.

In order to activate Wake on LAN on a system, you'll need to know its MAC address, which you can look up by running IPCONFIG /ALL from a command prompt. Look for the entry marked Physical Address and copy down the six pairs of alphanumeric characters displayed — you'll need this information later.

Network Prep
That does it for the system setup — now it's time to configure your network, which can be a little more complicated. Chances are, your system gets its IP addresses via DHCP, but in this case, you'll want to configure it with a static IP address to make sure the system is always available at a fixed address. If your router supports the DHCP reservation feature or allows you to specify an address lease time of forever, you can accomplish the same thing and continue to use DHCP.

Now you need to create a port forwarding rule in your router so the Wake on LAN signal can be directed to the right system. Choose a high-numbered port to avoid conflicting with any standard network traffic common on lower ports (like port 80 for HTTP, 53 for DNS and so on) and make sure the traffic on that port goes to the IP address you specified earlier. The exact steps for setting up this rule vary depending on your router, so check your documentation.

Now comes the tricky part, because in order to access your system from outside your network, you have to know the public IP address your ISP has assigned you. That's easy enough to look up (you'll find it listed within the Status page of your router), but if your ISP is like most, that IP address probably changes every so often, which means the address you see will be valid only for a limited time.

The simplest way around this problem is to set up an account with a Dynamic DNS provider, which will track your network's IP address changes and let you access it using a consistent domain name. (For more details on Dynamic DNS and how to set it up, check out our recent article on the subject.

You Can Do Magic
In order to wake a system out of its slumber, you need to send it a so-called "magic packet," a specially formatted packet that contains the system's MAC address over and over. There are lots of free utilities available to generate and send magic packets, but I came across a Web site that will do it without the need to download and install any software.

To send your system a magic packet, enter the MAC address you copied down earlier, your network's IP address (or Dynamic DNS domain name) and the port number you chose into the appropriate fields (you can leave the Subnet Mask field as is). Then click the Wake On Wan button, and within a second or two, your system will begin to power up. There's no way to get an acknowledgment that it actually worked, but if you have another system, you can test it right from home.

A couple of final thoughts — when waking your system while on the road, remember that it can take several minutes for the system to fully power up and re-establish all its network connections, so it may be a little while before it responds to your attempts at remote access. Also keep in mind that in order for Wake on LAN to work, the system must of course remain plugged into AC and your router.

As you can see, setting up Wake on LAN takes some doing, but once it's done, you can save some of the electricity and money it takes to run your PC without sacrificing the capability to access it remotely when you need to.



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