A MAC Address (or Media Access Control) is a unique serial number (or identification number) given to network hardware, such as a network adapter or any other device used to connect to a network or more prominently to identify itself. In some situations it is also known as an Ethernet Hardware Address or EHA.
The MAC Address is used to pass packets between devices in the same network directly. This process ensures the fact that the packet is first received by the physical device. You could say that an IP Address is similar to the MAC Address in that they are both allowing devices to connect to the same network safely and reliably. It works in the data link layer of the OSI model. Unlike an IP address, we cannot use a MAC address to determine the proximity or location of the system.
The first EHA or MAC Address was used by the Xerox Ethernet addressing machine. Because it uses 48 bits to be defined, there are over 280 trillion possible MAC Addresses, so you are not going to find two MAC Addresses that are exactly the same on the planet. There are three numbering standards for this address and each one uses the same type of numbering. They are called:
EUI stands for Extended Unique Identifier. Here are some of the technologies you might encounter that use a MAC Address:
The MAC Address, as opposed to the IP Address, cannot be changed and will always be the same for the respective piece of hardware, whatever that might be. At best, you can clone a MAC Address in a router if the network connection requires this information to be correct when connecting to the internet. All routers have this feature.
You are probably wondering how this MAC Address looks like. Just to give you an example: xx:xx:xx:xx:xx:xx. Each x in that sequence can be replaced by either a letter or a number to create a MAC Address. If you want to see what the MAC Address of your computer is, you can find this information by going to the control panel (Microsoft Windows) and accessing the network properties section. You will need this information in some cases, so it is a good idea to know where to look for it.
The MAC Address is assigned to the piece of networking hardware by the manufacturer based on certain algorithms and rules. The Address is than checked with the authority in this field to make sure that they are not releasing a network controller with the same MAC as another one that has been previously released, even if the chances of doing that are very slim.
So, the MAC Address has the simple task of making each device that is capable of connecting to a network unique. This ensures that you can connect to the internet at any time without any kind of problems caused by the fact that some other device is using the exact same identification number as you. To put it even simpler, it is like the license plate on your car. Remember the fact the your MAC address is invisible most of the time and in the internet only the IP address is used.
You can find more information about how to find your MAC address by reading this article. As said above, the first 3 bytes of the MAC address represents the organization that makes the hardware. See this list where you can find OUI of different vendors.