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WHAT IS A MAC ADDRESS?

What is a MAC address?

When you open a website or try to download a video from the internet, the site knows your location using your IP address, but the IP address does get it so far as to your router. Usually your router has more than one device connected to it, so it needs a way to distinguish the devices, this is where MAC address comes in. MAC (Media Access Control) address or burned-in address is a unique identifier assigned to a NIC (Network Interface Controller). Your router uses the MAC addresses of your devices to assign them private IP addresses for distinguishing them. When a NIC is manufactured it is assigned a MAC address. These MAC addresses are used for differentiating devices for network purposes. The MAC addresses follow the standards set by the IEEE (Institute of Electrical and Electronic Engineers- also referred as I-triple-E).

The default format of mac addresses is six set of two-digit characters, separated by hyphens but there are some different notations like:

1. Hyphen-Hexadecimal notation (default): 00-1B-44-11-3A-B7

2. Colon-Hexadecimal notation : 00:1B:44:11:3A:B7

3. Period-separated hexadecimal notation: 001.B44.113.AB7
Windows uses hyphen hexadecimal notation; Linux OS uses Colon-Hexadecimal notation and Cisco systems uses Period-separated hexadecimal notation.

The first 6 digits of a MAC address are called OUI (Organizational Unique Identifier) and they represent the manufacturer of the NIC, in our example 00-1B-44 are the first 6 digits, this means the manufacturer of our example NIC is SanDisk Corporation. Here are the OUI’s of some well-known manufacturers:

CC:46:D6 - Cisco Systems

3C:5A:B4 - Google, Inc.

3C:D9:2B - Hewlett Packard (HP)

00:9A:CD - HUAWEI TECHNOLOGIES CO.,LTD

Local MAC address

Although all NICs are manufactured with a physical unchangeable address. A network administrator can create a local address which overrides the burned-in original address in the local network. We can differentiate local and universal mac addresses by looking to the second least significant bit of the first octet. If that bit is 0, the address is universal if it is 1 the address is local. Therefore, that bit is also referred to as U/L (Universal/Local) bit. In our example the binary form of the first octet (00) is 00000000 the second least significant bit is, like all bits here, is 0 so our example address is a Universal address.

What can I do with this information?

You can use MAC addresses for extra network security, for example you can limit the access of your network to certain devices using their MAC addresses, this way even if a cyber-criminal hacks into your system, he/she cannot access your systems without also physically getting access to your permitted devices.

How to check your MAC address?

You can easily check your MAC address and find out the manufacturer of your NIC using that address. In Windows all you need to do is open the command prompt and type in “ipconfig /a” and it will give a bunch of information including the MAC address of your device. If you are using a MAC computer, you should open the Terminal and type in “networksetup-listallhardwarereports” for seeing your mac address.
 

Murat GÖĞEBAKAN
Undergraduate in Bogazici University Management Information Systems



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