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What’s a MAC Address?

A MAC address is a unique 48-bit hardware identifier burned into every network interface card, used to direct network traffic to the correct device. Expressed in hexadecimal and separated by colons or dashes for readability, MAC addresses operate at the hardware level across Ethernet and other network protocols.

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About this video

When multiple devices share a network, there must be a reliable way to direct traffic to the correct destination. MAC addresses solve this problem by giving every network interface card a unique 48-bit identifier, allowing a sender to tag outgoing data with the intended recipient's address so that all other devices on the network know to ignore it. A 48-bit address is represented as 12 hexadecimal characters, typically displayed in pairs separated by colons or dashes — a formatting choice made purely for human readability rather than any technical requirement. The underlying value is identical regardless of which separator is used. MAC addresses are burned in by the network interface card manufacturer, not assigned by the device owner or network administrator. This means the address is permanently embedded in the hardware before it ever reaches the end user, and in many cases the NIC manufacturer is a separate company from the maker of the device it ships inside. Because MAC addressing operates at the hardware level, it is used by Ethernet as well as several other networking protocols, though not all protocols rely on MAC addresses for device identification.

What you'll learn

What's covered

MAC Addresses

Aligned to

CompTIA Network+
1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.
Cisco CCNA
1.13 Describe switching concepts
Cisco CCST Networking
4.5 Explain basic switching concepts
3.3 Describe endpoint devices
Cisco CCST Cybersecurity
2.2 Explain how network addresses impact network security

Key terms

Media Access Control
MAC
A sublayer of the Data Link layer that controls how devices on a network gain access to a medium and transmit data.
Network Interface Card
NIC
A hardware component that connects a computer to a network.
Data Link Layer
Layer 2 of the OSI model responsible for node-to-node data transfer and error detection on a single network segment.
Burned-In Address
BIA
A MAC address permanently assigned to a network interface card by its manufacturer at the time of production.
Hexadecimal
Hex
A base-16 number system using digits 0–9 and letters A–F; each hex digit maps to exactly 4 bits, making it a compact shorthand for representing binary data.

Transcript

When we start communicating with more than one device, we're going to need to address the device that we want to speak to. We need some sort of addressing, and a MAC address is one of those addressings that we can use.

If one machine on this network is talking to another machine, we see with the hub that all other devices get that message, which has some security concerns, and we'll address that at a later time. But for now, let's just say that this computer needs to be able to address this computer, and then all other computers need to know that they need to ignore the message.

So how do we do that? What we can do is we can have a MAC address on every single machine. So that way, when this message gets sent out, we will tag it with what MAC address we're going for. So we're going to tag it with this MAC address right here. And then when all of these other devices see that message come in, they're going to ignore it, except for this one will process that message, because it's destined for the MAC address that is this computer.

How a MAC address is written

MAC addresses are 48 bits long, 48 ones and zeros all lined up like that. However, that's really hard to read and relay that information. So instead we use hexadecimal. So this is the equivalent in hexadecimal form. Of course, that also is a fairly long stretch of characters there. So what we do is we translate that into something like this, where we put colons in between every two characters.

And so what we have is 48 bits. However, it breaks down into 12 hexadecimal numbers right there. You'll also see sometimes we have dashes in between. It doesn't really matter what kind of separates it out, because it's just so we can read it better. It's not so the computer can read it. That's just the way the computer is displaying it.

Where MAC addresses come from

So then the next question is, where do these MAC addresses come from? Do we assign them to these computers? And the answer is no. It's what's called a burned-in address. So each one of these devices has a network interface card. That's how it can connect all together. So whatever the manufacturer was of that network interface card, and many times that's different than the actual device manufacturer, it's a different company that manufactures those NICs. So whoever manufactured those NICs burned in an address. So it comes with an address already pre-assigned to it.

Now, there are several different technologies that use MAC addresses, one of them being the Ethernet protocol, but there are other protocols. Some of them do use the MAC address, while others use other types of addressing. So just realize that this isn't just a given.

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