How to find the MAC address of an offline computer?

There are multiple ways of getting the MAC address of a system that is on either locally or remotely. But, what if your system is off, you do not have physical access to the system and you wanted to turn it on remotely using Wake on Lan(WOL)? In order to turn your computer on remotely using WOL you need to know the MAC address of that system. If you are not planned this ahead of time, finding the systems MAC address might not be very easy. What are your options?

Your first option is your router. There are several ways that you can use your router to locate the MAC address. These options depend on the router. Here are some of these options:

  1. Access Control List: Some routers log every allowed device into their Access Control List regardless they are currently on or not. For example Netgear R7000. This would be one of the easiest way to get the MAC address of an offline system.
  2. Router Logs: Some routers log the MAC address of each local connection.
  3. ARP Table (more below): Some routers keep the MAC address of an offline computer in their ARP table even long after the system goes offline. These are usually advanced routers.

If you have another system that you can access, you can look at that system’s ARP table to see if the offline system is listed. Windows 8.1 system that I checked kept the offline system in its ARP table hours after it’s been turned off.  You can obtain the ARP table using the following command on Windows Command Prompt, or Terminal on OS X and Linux:

arp –a

If you have another Windows system that you can access, and if that system has interacted with the target system, you might get lucky. Search the registry of the system that you have access for the computer name and ip address of the target system. For example, Windows Media Player’s Play To functionality keeps a record in the registry for the systems it previously interacted. On Windows 7, it is located at HKLM\Software\Microsoft\Windows Media Player NSS\3.0\Devices, and it stores MAC address, ip address and computer name along with some other information. Device names under this key are MAC addresses of those systems/devices.

Once you find the MAC address of the offline system, you can try a WOL tool to awaken it.

You can get more information about Wake on LAN at Wikipedia.

Happy hunting.

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