What Is a MAC Address? What Is a NIC?

So the question is often asked: What is a MAC address?

An interface to a network from a computer or server or printer (or really anything that connects to a network) that interface enables that computing device to send and receive data across the network.

It's typically referred to as the "network interface" All modern computing devices have a network interface either wired to connect to an Ethernet network using Ethernet cables like these or wireless to connect to a wireless Access Point (AP).

What is a NIC?

The network interface traditionally has been called a Network Interface Card or NIC for short because the interface in most older machines up to this point came on a separate expansion card.

However for many years now motherboards of both laptops and desktops have "onboard" or rather built-in network interfaces. Most texts today still call them NICs whether they're built-in or whether they're an actual separate card that's used on the motherboard of a server or a PC or a printer.

This is a picture of an onboard NIC that's already built into the motherboard for a desktop PC just gave me give you a little bit of an idea of how that looks.

There are several responsibilities that NICs have: They provide connection to the network media of course (either network cables or wires or wireless using radio frequency waves or they could be Bluetooth, etc.) they provide connectivity.

NICs also have a physical address known as a MAC address that stands for Media Access Control which I'm going to show you and talk more about shortly in this same video these NICs enable communication with other devices on the network.

Finally NICs take data from the operating system and they encapsulate that data into a frame suitable for traversing that physical layer that physical aspect of the network whether that's the cable or the wireless.

In fact, if and when you study the 7 layers of the OSI model or the layers of the TCP/IP model, you need to know upfront that most of the work that takes place in those layers working together is really all done within that NIC and it's usually its onboard processor chip or chips that do all that work with the with the layers of the OSI model or the layers of the TCP/IP model.

More on that in other posts and in the bonus section of the free mini course if you manage to take advantage of getting access to that.

What Is a MAC Address?

So let's talk about the MAC address on every NIC.

The analogy that's usually used with MAC addresses and IP addresses in the networking field is that they are similar to the name of a student in a classroom - that's always the analogy that's used.

The teacher and the other students in that classroom may not know how to find or address one another if they don't have a name for each other if they don't know what to call each other. So each person has a name each student and the teacher or teachers have a name.

A MAC address is the same as the name hard assigned to each NIC card or each NIC interface on a motherboard.

On every NIC burned onto a ROM chip is special firmware containing a unique identifier with a 48 bit value called the Media Access Control address or MAC address for short.

The OUI (1st Half of MAC)

No 2 NIC's ever share the same MAC address EVER! Any company that makes NIC's that manufactures them must contact the Institute of Electrical and Electronics Engineers (also known as IEEE) and request a block of MAC addresses which that company then burns into the ROMs or the ROM chips on its NIC's.

Many NIC makers also print the MAC address on the surface of each NIC like you see here. MAC addresses are written with a hexadecimal digit because each hex character represents 4 bits each and it takes 12 hex characters to represent 48 bits.

The MAC address on this NIC card shown here is:
004005A7BA71

Although in print we represent the MAC address 00-40-05-A7-B7-71 (we put hyphens between every 2 hexadecimal characters in that MAC address to make it easier to read).

The first 6 digits in this example 00-40-05 represent the number of the NIC manufacturer. Once the IEEE issues those 6 hex digits to that manufacturer often called the Organizationally Unique Identifier (or OUI), no other manufacturer may use those 6 digits in that order.

The "Device ID" (2nd Half of MAC)

The last 6 digits in this example are A7-BA-71

Well those are the manufacturers unique serial number for that specific NIC. This portion of the MAC address is often called the "Device ID" so the first half is the OUI first half the MAC address is the OUI the Organizationally Unique Identifier and the last half the last 6 digits is the Device ID for that specific NIC card.

Would you like to see the MAC address for your NIC on the computer that you're on now?

If you have a Windows system search for the command line program you can search for CMD also called a Command Line Interface.

And once that text command program is open it'll look similar to this you're going to type in "ipconfig /all" and hit ENTER. You're going to do that from the command prompt to display the MAC address like you see here.

Now note that in the IE config output the MAC address is always called the "physical address" that's how it's referred to when you reference it on a computer like this.

So that's the basic functions of the NIC card and what we're referring to when we talk about the MAC Address on a computing device or any device connected to a network.

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