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Ethernet hardware address

Last revision July 3, 2007

Every ethernet interface adapter has a globally unique hardware address assigned by the manufacturer, consisting of a set of six hexadecimal pairs (hexadecimal means numbers in base 16, which are represented by the normal digits 0 to 9, plus the letters a to f). This hardware address is often printed on a label affixed to the device or shipping box. Otherwise, it can be found during using a driver or utility program (see below).

Because this hardware address is the only truly unique identifier for your device on the network, it is the key to your network access via the Dynamic Host Configuration Protocol (DHCP). During the self-registration procedure (for Macs and Windows) or manual registration (for other devices), your hardware address is discovered or provided and becomes associated to a specific network IP address valid on the Earth Sciences network that is assigned for you in the registration database.

Selecting DHCP as your configuration method (the default for all modern computers, printers, and other network devices) causes your computer to broadcast its ethernet hardware address on the network when it starts up. The campus DHCP servers receive this broadcast and use the registration database information for your hardware address (updated to them every 15 minutes) to automatically provide your computer its assigned IP address, router information, and name server information so it can function on the network.

When your registered computer moves to another network on campus, or accesses the wireless network, the same DHCP procedure is used to assign it a temporary IP address valid on that network, assuming it was registered with the roaming attribute.

Stanford's DHCP servers do not provide IP addresses to random devices that are plugged into our network. They only respond to broadcasts from registered devices.

Finding the ethernet hardware address for your system

MacOS X

First, open the System Preferences application (often in the dock, otherwise accessible from the Apple menu). Click on the Network preference pane.

There are two drop-down menu options at the top of the Network pane, one named Location: (pre-defined configuration options for different networks), and the other Show: (which interface is used for your connection). Make sure that the Automatic: option is selected in the Location: menu.

To find the ethernet hardware address of your wired ethernet interface, select the Built-in Ethernet item from the Show: drop-down menu. Below the drop-down menus, there is a series of tabs, each of which can be clicked to show different configuration parameters. In MacOS X 10.3 or 10.4, click on the Ethernet tab. Your ethernet hardware address will be displayed after the heading Ethernet ID. In older versions of MacOS X, click on the TCP/IP tab; now your ethernet hardware address will be shown at the bottom of the window, labeled Ethernet Address.

To find the ethernet hardware address of your wireless interface, first select the AirPort item from the Show: drop-down menu. Now click on the AirPort tab. The AirPort ID item displays your wireless ethernet hardware address.

Windows 2000, XP, 2003, or Vista

First, open a command-line (DOS-style) window to type commands by running the cmd program from the Run item in the Start menu. Inside the command-line window that it opens, type the command ipconfig /all and press the RETURN key.

This will report information on all your network interfaces, wired and wireless. Each interface is identified, and then has various parameters listed below. The value reported in the Physical Address line is the ethernet hardware address for that interface.

Unix/Linux computers

Unix and Linux computers usually report the ethernet hardware address on the console during the configuration stage of the boot process.

Legacy operating systems

See this page for information about determining the ethernet hardware address for older operating systems that are no longer supported on the Earth Sciences network.

More information

More information on obtaining the ethernet hardware address for a Macintosh or PC can be obtained from the following web sites. These sites contain screen shots showing the programs listed above.

 


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