Introduction
What is
Wake On LAN? Wake on LAN, or WOL, is the ability to send a signal over a local area network (LAN) to power up a PC.
Wake on WAN
is the ability to send that same signal over a wide area network (WAN),
such as the Internet, to trigger power-up of a PC on a private LAN.
Perhaps you have a PC at home that you don't want to leave
powered on, yet may need to access while at work. Maybe you saw Al
Gore's video, and you want to conserve energy and leave your PC off
except when you need it. Certainly, your PC is more secure from hackers
when it is off.
In order to take advantage of Wake On LAN/WAN technology, there are
multiple steps to perform. This guide lists those steps, covering BIOS
configurations, software, testing, routing, and security. The goal here
isn't to cover every aspect of Wake On LAN/WAN technology, but to
provide understanding and tools to make it work on your network.
You'll notice that testing comprises multiple steps in this guide. I
can't emphasize enough the importance of making one change at a time,
and then testing the effectiveness. Trust me, you'll thank yourself
later for your patience and attention to detail now. I have been
involved in far too many network changes that had to be completely
re-done due to poor testing and methodology. If you check your work at
each step, you can avoid doing it all over again later.
To find your way through all the options, it's helpful to reference
the OSI model for computer networking. As you can see in Figure 1, the
OSI model specifies seven layers. WOL plays primarily in Layers 1-4.
Figure 1: A chart showing the OSI model
(CCNA Intro Exam Certification Guide, Cisco Press, 2004, Wendell Odom, p34)
At Layer 1, (the Physical layer) both the PC to be turned on and the
PC sending the WOL signal need to use wired Ethernet connections.
At Layer 2, (the Data Link layer) WOL uses MAC (Media Access Control)
addresses to turn on a specific PC. The MAC address is critical, as a
PC in the off condition doesn't have an IP address. IP addresses are
loaded in memory, whereas MAC addresses are burned into the card.
The frame sent to the target PC carries a special datagram, called a
"magic packet", which triggers an Ethernet card (NIC) to power up a PC. A
WOL packet sent over the Internet will hit your router first. Your
router will take the packet, strip the WAN IP, and send the packet to
the Layer 2 MAC address on your LAN.
It's important to note that WOL doesn't work over wireless networks.
Although both wired and wireless networks use MAC addressing, the format
of a wireless frame is different than the format of a wired frame.
Specifically, there is additional information carried in the header of a
wireless frame that interferes with the magic packet frame, preventing
the target machine from detecting the wakeup signal.
At Layer 3, (the Network layer) WOL works best when directed at a
broadcast address. The broadcast address in most home and small business
LANs ends in .255. For example, a gateway router with an IP address of
192.168.1.1 will typically have a broadcast address of 192.168.1.255.
This guide assumes your LAN uses a private IP address space, such as
10.x.x.x, 172.16.x.x, or 192.168.x.x. Typically, you'll have a gateway
router providing NAT (Network Address Translation) through the public IP
address provided by your ISP.
The challenge at Layer 3 (which handles IP addresses) is transmitting
a Layer 2 frame, destined for a private IP broadcast address, across
the Internet. Private IP addresses are not transmitted across the
Internet, and broadcasts are often blocked.
The solution lies in Layer 4, the Transport layer. This layer
specifies transport type (TCP or UDP) and port numbers. Communication
across an IP network, the Internet included, uses both IP addresses and
ports. Successfully transmitting a WOL signal over the Internet requires
knowing the UDP port used by your WOL utility, and forwarding that port
through your firewall.
Below are eight steps to follow to enable Wake On LAN/WAN technology
on your network. Before you start, it will be helpful to have a solid
understanding of your LAN and its elements. Taking the time to map and
document the details of your network will come in handy. Even a small
LAN of a half-dozen nodes has numerous key details, including subnet
information, DHCP settings, MAC addresses, installed OS's, router
configurations, etc.
Step 1 - Enable Wake on LAN
Most motherboards today have a built in NIC and support Wake on LAN
functionality. You'll have to go into the BIOS Power Options to enable
it. The process is different in each motherboard, but pretty
straightforward.
On an Intel CPU ASUS P4C800 board, the option is called
Power On By PCI Devices in the APM (Advanced Power Management) menu. On an AMD CPU MSI K8N board, the option is called
Resume by MAC LAN.
Figure 2 below is screen shot from a laptop BIOS. You can see the option is called
Power Management and there is a selection for Wake on LAN.
Figure 2: A view of a laptop BIOS
If you're using a separate PCI LAN card, you'll have to enable WOL
functionality for PCI devices in your BIOS. Note that if you're using an
older motherboard with a PCI 2.1 or older bus, you'll likely need to
connect a 3-pin WOL cable from the NIC to the motherboard. This cable is
typically not needed in newer computers using a PCI 2.2 or newer bus.
Finally, check the Advanced Properties of your network card. In
Windows, go to Start-Settings-Network Connections to ensure Wake
functionality is enabled. An example is shown below in Figure 3.
Figure 3: The Advanced Properties tab of the NIC properties
Step 2 - Collect your MAC address
From the PC on which you want WOL functionality, go to the command line (Start-Run-cmd) and type
ipconfig /all. This will tell you the IP and MAC of the NIC you want to receive the WOL signal.
It's handy to store this information in a file you can access from
the PC you'll be using to power up the target PC. The MAC address will
be the
Physical Address in the form XX-XX-XX-XX-XX-XX. In the below example in Figure 4, the Physical Address is shown as
00-12.
I deleted the rest of it; normally, you'd see the full six sets of
characters. A sample MAC looks like this: 00-01-02-55-77-B3.
Figure 4: The results of the "ipconfig /all" command
Step 3 - Download and install software
There are a lot of useful utilities for WOL. The intent of this guide
isn't to review or recommend software, but to show you how to make it
work.
I use two WOL utilities,
mc-wol.exe, and AMD's
Magic Packet Utility. I like the AMD Utility (
www.amd.com/us-en/assets/content_type/utilities/magic_pkt.exe)
as it allows for creating and saving a file of target PC MAC addresses.
This comes in handy, allowing you to fire up the application, open your
file, grab the MAC, and power up.
The other tool I find invaluable for network troubleshooting is Ethereal, now known as Wireshark (
www.wireshark.org). These three tools are freeware and easy to use.
Step 4 - Test your configurations!
When making changes to your network, you can't be too thorough. Make
one change at a time, and test each one from controlled scenarios as
much as possible. Turn off your PC while at home and test WOL to watch
the PC turn on!
mc-wol.exe is a simple DOS based utility and works well
over the LAN. Using another PC on the same LAN as the target PC, start
up the command line and go to the directory where you saved the
mc-wol.exe
utility. From the command line, execute the application with the MAC as
its argument. For example: MC-WOL 00:01:02:55:77:B3 Note that the
command and MAC address aren't case-sensitive, so you can skip the shift
key.
You should observe the target PC powering up almost instantly upon
hitting enter. If not, stop here and go back to Step 1. WOL won't work
over the WAN if it doesn't work on the LAN. Measure, in seconds, the
amount of time from power-up to boot completion. Knowing this will make
the wait when you've sent a WOL signal easier.
Step 5 - Configure your router
There are two parts to WOL router configuration: optional and required changes. We'll discuss the optional configurations here.
To send a WOL signal over the Internet to your LAN, you need to know
your Public IP. Unless you're paying extra for a static public IP, your
ISP can change your public IP address whenever it wants, often when you
reboot your router.
Dynamic DNS is a free and useful way to keep track of your Public IP
address. If you have a Linksys or D-Link router, odds are that it has
Dynamic DNS (DDNS) functionality. Both work with a free public website,
www.dyndns.org.
Set yourself up with a free account and you'll have a fully qualified
domain name that won't change, even when your ISP changes your IP.
Enable DDNS and enter your account information into your router, and
your router will keep your IP tied to your new domain name. There are
other Dynamic DNS services that also work.
If your router doesn't support Dynamic DNS, you can download a
PC-based client from Dynamic DNS to allow a PC on your LAN to keep your
public IP associated with your domain. However, your domain can't be
updated if your IP changes while your computer is turned off.
Static DHCP is a useful router configuration for a PC that you want
to work with remotely. I like this better than setting a static private
IP. Static DHCP lets your PC synch with the router and get the correct
DNS information, saving the hassle of configuring it on the PC. Most
routers allow you to specify a MAC address and assign it an IP address.
When properly configured, your PC will now always have the same IP, but
get the current and correct DNS IPs. Further, your router will have the
MAC address of the target PC stored in its config.
Set up your router to allow for remote login. This is a security
concern, but it comes in handy while troubleshooting your home LAN
remotely.
Ping is a very powerful tool that is very useful for troubleshooting.
The default setting on router and PC firewalls is to disable ping or
echo replies. Having this functionality enabled helps verify the
reachability of your LAN and PC.
Many routers have the ability to perform simple diagnostics,
including a ping test, similar to what's shown in Figure 5. If your PC
firewall allows pings, it will come in handy when you're trying to see
if your PC is on or off. Familiarize yourself with this aspect of your
router. It is useful to be able to log into your home router remotely
and ping your target PC.
Figure 5: A router ping test
Last, if your router has a logging capability, you can use it to see
if your WOL packets are hitting your router and being forwarded to your
LAN. It's definitely a feature that you'll find useful if there are
issues.
Step 6 - Configure port forwarding
Configuring port forwarding on your router is a required change; WOL won't work without it.
WOL uses UDP as its Layer 4 transport, but the port varies based on the utility. The
mc-wol.exe utility uses UDP port 65535. AMD's
Magic Packet Utility uses UDP port 2304. There is a Linux tool, aptly named
wakeonlan, that uses UDP port 9.
An easy way to find the port is to use a packet sniffer utility to
see which port is used. Ethereal (now Wireshark) is probably the best
known, and a very powerful free download. If you're into networking, it
is an invaluable troubleshooting tool. You may find this tool comes in
handy if you're using a different WOL utility and need to find the port
number.
Figure 6 below is the Wireshark capture of a WOL packet. The areas
titled MAC ADDRESS and IP Address are blanked out in the example,
because you'll see your own MAC and IP addresses when you run it. The
key is the
Dst Port (Destination Port). This is what you're looking for.
Figure 6: Wireshark's packet capture showing the destination port
Once you have the port number, you have what you need. You'll need to
go into your router's port forwarding menu and set up a rule to forward
UDP packets sent to the WOL port to the broadcast IP address of your
LAN.
Some routers don't allow broadcast IPs to be used as a target IP.
This is where having Static DHCP comes in handy. If you have configured
Static DHCP, and your router has the MAC of your target PC, you can
configure your router to forward the WOL packet directly to the IP
address of the target PC.
Figure 7 below is a screen shot from a Linksys RV042 router. Port
forwarding is configured in the Setup menu under the Forwarding tab.
Figure 7: Setting up port forwarding on a Linksys RV042 router
Figure 8 below is a screen shot from a Zyxel P-334WT router with
several port forwarding rules configured. Port forwarding is configured
in the Network menu under the NAT-Port Forwarding tab.
Figure 8: Setting up port forwarding on a Zyxel P-334WT router
Step 7 - Test again!
Now that you think you've configured everything, test it. Start with
ensuring you can access the target PC. If you can ping from your router,
double-check and ping your target PC.
Now you've reached the moment of truth. Turn the target PC off. You
can remotely turn off a Windows PC via Remote Desktop Connection by
right-clicking the menu bar and selecting Task Manager. You'll see a
Shut Down option similar to Figure 9.
Figure 9: The Shut Down option on the Task Manager
Other OSes have similar options. Many Linux distributions have a power button at the top right, similar to Figure 10.
Figure 10: The power button on a Linux distribution
Okay, the PC is off. You can double-check that by sending a ping from your router to the target PC.
Now send the WOL signal to the target PC. If using the AMD Utility,
you'll enter your Dynamic DNS domain, or Public IP, and the MAC address
of the target PC, as in Figure 11 below. Note the time in seconds and
reference the measured time—from power-up to fully booted—you previously
recorded. You'll be glad you collected this as you wait the endless
seconds before you can remotely login.
Figure 11: Sending the WOL signal
If you can log in, congratulations! You've remotely powered up a
PC. If not, now is the time to start utilizing the tools discussed
previously.
Leveraging the tools in your router, especially ping and log
functionality, will help you find a problem. Start by looking at the log
of your router. See if it received a packet from your remote PC and
forwarded it per the rule you configured.
Step 8 - Security is important
Powering up a PC remotely, opening ports on your firewall, enabling
remote login, and enabling ping capabilities all expose your PCs and
network to the world. It's up to you how you manage that risk. For
example, you can turn off ping capability on your router and disable
your port forwarding rules. If you have enabled remote login to your
router, you can then turn on the ping and forwarding rules when you need
to power up a PC, and turn them off when you don't.
Regardless of OS, you need to set up the PC you subject to WOL
to require a username and password for remote login. Windows Remote
Desktop Connection is a useful way to remotely access a PC, and should
be set up with a username and password. VNC software should always be
configured to require a password on remote login.
Use secure passwords. Change the passwords on your router and PCs to
unique, 8 or more character mixtures of uppercase and lowercase
alphanumeric characters.
Test it at home before you leave your house with your PC off, hoping
to turn it on remotely. Then, test it remotely with someone else at home
to turn on your PC if WOL isn't working.
When all is said and done, you'll have a pretty cool solution: the
ability to remotely fire up your PC with a keyboard from anywhere on the
Internet. Plus, you'll save money and electricity by leaving your PC
off when you don't need it.
