/ What is a MAC address?

What is a MAC address?

Celeste Stewart Until the home computer networking revolution, most computer users had no real need to learn about MAC addresses. In the office environment, IT techs handled the networking requirements and dealt with MAC and IP addressing. But once families decided that one home computer wasn’t enough, the average computer user suddenly had to learn about basic networking concepts.

In order to create even the most basic network, computers require a network adapter. Once a network adapter is installed in each computer, two or more computers can speak with each other through wired or wireless connections into the network adapter. The MAC address is the unique identifier associated with each network adapter.

MAC addresses aren’t simply random numbers. They follow a specific hexadecimal pattern of 12-digits (48 bits) in the following format (with MM signifying Manufacturer numbers and SS signifying Serial numbers):

MM:MM:MM:SS:SS:SS

Occasionally, MAC addresses use a format such as:

MMMMMM-SSSSSS or MM-MM-MM-SS-SS-SS

For example:

In the MAC address “00:13:10:a2:bf:a6,” 001310 represents the manufacturer of the network adapter (in this case Cisco-Linksys) while a2bfa6 represents the serial number.

When you first purchase your networking hardware, the MAC address information is usually easy to find. For example, if you buy a new router, the MAC address will be included with the router’s documentation. In addition, a label with the MAC address will likely be on the router itself. Similarly, any hardware that you buy that uses a MAC address should have similar information and labeling. For example, if your laptop came with a wireless network adapter preinstalled, you’ll likely find a label on the bottom of the laptop marked “wireless LAN” or “MAC address.”

If you can’t find a label, you can use the ipconfig command to discover the IP and MAC addresses of your computer. In Windows 2000 and above, go to the Start button and select Run. (In Windows Vista, you may need to go to a Command Prompt first. Start > Programs > Accessories > Command Prompt.) Type in: ipconfig /all

This will display a list of all of your IP and MAC addresses for various adapters installed on the system. The MAC address will be listed as a “physical address.” Each network card will have its own physical address. In addition, you will likely see at least one virtual MAC address.

MAC address tracking is often performed both by your ISP as well as within your home computer network. For example, if you have a cable modem, you will likely need to register it with your ISP as part of the setup of your Internet connection. This step is part of creating your Internet access account. The ISP will recognize your device and grant you access to the network. However, if you replace your cable modem, you’ll have a new device with a new MAC address. When you try to connect to the Internet, you’ll likely be denied access because your device’s MAC address doesn’t match the one you’ve previously registered. A quick phone call to the ISP is usually all that’s involved in registering your new MAC address.

Your home networking software also monitors the various MAC addresses of connected computers. For example, you can set up your network to only allow “trusted” MAC addresses to connect to your computer. By entering the MAC addresses of your networked computers, you will exclude other computers from connecting to your network.