How to Determine Your Ethernet or Wireless Hardware Address

This document describes how to determine your computer's (or printer's) Ethernet or Wireless hardware address(es). You need to know your hardware address(es) in order to register your computer or printer in the Princeton University Host Database.

Contents

1. What is an Ethernet or Wireless Hardware Address?
2. The Easiest Way to Discover a Hardware Address
3. Forging (Spoofing, Cloning) Another Hardware Address is not Acceptable

• Windows 95, 98, ME
• Windows NT 4.0
• Windows 2000, XP
• Windows Vista
• Mac OS X 10.4, 10.5
• Sun

If your computer has both an Ethernet interface and a Wireless interface, each will have its own unique hardware address.

An Ethernet or Wireless hardware address is a 6-byte hexadecimal number; for example: 0x080007A9B2FC. (Each byte is written as two hexadecimal digits, so there are twelve hexadecimal digits; each hex digit is a number from 0-9 or a letter from A-F. A leading '0x' may be written to make explicit that the following digits should interpreted as hexadecimal.)

Ethernet and Wireless hardware addresses are often written in other forms, to make them easier to understand. It is common to leave off the leading '0x', and also to separate the six pairs of digits with colons or dashes, like: 08:00:07:A9:B2:FC or 00-00-94-ba-0e-cc. When using colons or dashes to separate the address into six pairs, sometimes any leading zero in each pair of digits is dropped; e.g. 8:0:7:A9:B2:FC or 0:0:94:ba:e:cc. (Note that when dropping leadings zeroes, '00' becomes '0' -- you never completely eliminate any of the six pairs of digits.)

Do not confuse an Ethernet or Wireless hardware address with an Internet Protocol ("IP") address; that's a number assigned to some computers and printers by the Princeton University, and looks something like: 128.112.1.2 or 140.180.1.2. Your Ethernet or Wireless hardware address is also not your email address, which typically looks something like rfraggle@princeton.edu.

If your computer or printer has a built-in Ethernet or Wireless interface, you may find a label attached to the back or bottom of the computer displaying the hardware address.

If you find a label, make sure it really is a hardware address; the section above describes what an Ethernet or Wireless hardware address looks like. For example, if you see letters of the alphabet other than A-F, you can be sure you're not looking at an Ethernet or Wireless hardware address; perhaps it is a model number or serial number for your computer.

In some cases, you will not find a hardware address displayed on the box, the Ethernet or Wireless interface, or the computer or printer. (Or you may have discarded the box, and opening the computer or printer to examine the interface card inside may not be a good choice.) In these cases, there is usually software you can run on the computer or printer that will display the Ethernet or Wireless hardware address. Instructions for some popular configurations appear below.

Many devices can be reconfigured so that instead of using the hardware address assigned by the manufacturer, they instead forge another hardware address of your own choosing. This is sometimes called "spoofing" or "cloning" a hardware address, particularly when the forged hardware address is one that belongs to another device.

Because a device's hardware address is one of the most important ways the device is identified on the campus network, forging a hardware address is not acceptable on the campus network. No device attached to the campus network should be configured to forge its hardware address; instead, every device attached to the campus network should use the unique hardware address assigned to it by the manufacturer.

The process of obtaining your ethernet address is fairly simple in Windows 95, Windows 98, and Windows ME. You need to have, at least, installed the Microsoft TCPIP protocol to use this method. If you have installed the MS TCPIP protocol do the following:

1. Click on Start.

2. Click on Run.

3. In the command line box which appears, enter the following and press the Enter key:

           winipcfg
   

4. A box will appear with a variety of information. Check the pull-down menu near the top to verify that your Ethernet interface is selected; if it is not, then select it in this menu.

5. Look for the line labelled Adapter Address. This is your Ethernet interface's hardware address. It will be written out completely as 6 pairs of 2 digits separted by hyphens. Write it down.

6. Click on the X in the top right-hand corner of the box to close the windows. You are now finished.

Troubleshooting

If you are unable to see your Ethernet interface in the window displayed by the winipcfg command, refer to the Help Desk solution: http://helpdesk.princeton.edu/scripts/tpm/solution.pl?ID=5094.

You can find your ethernet address using Microsoft's ipconfig utility:

1. Click the Start button.

2. Select Programs and then select Command Prompt.

3. At the C:\> prompt, enter the following then press the Enter key:

           ipconfig /all
   

4. Your machine's ethernet address is listed as the Physical Address.

5. To close the Command Prompt window, enter the following at the C:\> prompt then press the Enter key:

           exit
   

You can find your machine's Ethernet or Wireless hardware addresses using Microsoft's ipconfig utility:

1. Click the Start button.

2. Select Programs and then select Accessories/Command Prompt.

3. At the C:\> prompt, enter the following then press the Enter key:

           ipconfig /all
   

4. Your machine's Ethernet or Wireless hardware address is listed as the Physical Address.

5. To close the Command Prompt window, enter the following at the C:\> prompt then press the Enter key:

           exit
   

You can find your machine's Ethernet or Wireless hardware addresses using Microsoft's getmac utility:

1. If your device is a Dell laptop, ensure it is plugged into an electrical outlet; if it is not plugged in, the device's Ethernet address will not be displayed.

2. Click the Start button.

3. In the Search box, enter the following then press the Enter key:

           cmd
   

4. At the DOS prompt, enter the following then press the Enter key:

           getmac /v
   

5. Your machine's Ethernet or Wireless hardware addresses are listed as the Physical Addresses.

6. To close the Command Prompt window, enter the following at the C:\> prompt then press the Enter key:

           exit
   

To display your Mac's Ethernet or Wireless hardware addresses:

1. Make sure that the network interface you're interested in is part of the current location, and is turned "on":
   1. Open the System Preferences application in the Apple menu. (It's also available in the Utilities folder, and sometimes in the Dock.)

   2. Click the Network icon.

   3. In the Location pop-up menu, select a location that includes the network interface of interest.

      For Mac OS X 10.4: You can verify that a network interface (port) is a member of a location by selecting that location, then in the Show pop-up menu, selecting Network Port Configurations. Verify that network interface of interest appears in the port list, and is turned "on" (its checkbox is checked).

      For Mac OX X 10.5: You can verify that a network interface (port) is a member of a location by selecting that location, then verifying that the network interface of interest appears in the network ports list on the left side of the window. Verify that the interface's status (which appears in grey just below the name of the interface) is anything other than "Inactive."

   4. If you made any changes in this window, click the Apply button in the lower right corner of the window.

   5. If you made any changes in the Network pane in System Preferences that you won't want to retain, make a note of them now, so you can undo them later.

   6. Once you've verified that the network interface you're interested in is part of the current location and is turned "on" (in 10.4), or is anything except "inactive (in 10.5), you can select Quit System Preferences from the File menu.

2. Launch the System Profiler application This program is normally located in the Utilities folder, which in turn is located in the Applications folder.

3. In the Contents pane on the left, select Network.

4. Displayed in the upper-right pane is a list of each of the Mac's network interfaces that are part of the current network location and are turned "on" (in 10.4), or anything except "inactive" (in 10.5).

   In this upper-right pane, select the item for the Ethernet or Wireless interface in which you are interested.

5. Displayed in the lower-right pane is information about the selected network interface.

   Each interface's hardware address is the value labelled Ethernet address, MAC address, or Hardware (MAC) address This is true even if the device is actually a wireless interface.

6. Quit the System Profiler application.

7. If earlier you changed any settings in the Network pane of System Preferences (e.g. to make a particular network interface active) and you wish to change it back, do so now.

If you have root privileges, the following command will show the Ethernet address for each Ethernet interface that exists on the system.

   # /usr/sbin/ifconfig -a

   lo0: flags=1000849 mtu 8232 index 1
           inet 127.0.0.1 netmask ff000000 
   hme0: flags=1000843 mtu 1500 index 2
           inet 192.168.1.2 netmask fffffc00 broadcast 192.168.1.0
           ether 8:0:20:4:5:6

Alternatively, reboot the machine. When it boots, it will write the Ethernet address to the console, to /var/adm/messages, or both. For example:

    unix: SunOS Release 5.8 Version Generic_108528-15 64-bit
    unix: Copyright 1983-2001 Sun Microsystems, Inc.  All rights reserved.
    unix: Ethernet address = 8:0:20:1:2:3
    ...