What is a MAC Address, and How Do I Find It?

What is a MAC Address?

The MAC address is a device's physical address, which uniquely identifies it on a specific network. MAC is short for Media Access Control and is also referred to as a hardware address, physical address, or burned-in address (BIA). The MAC address works on the OSI model's data link layer. The Address Resolution Protocol (ARP), a layer 2 communication protocol, maps the MAC addresses to the IP (Internet Protocol) address.

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In IEEE 802 standard, the data link layer is split into two sublayers: 

• Logical Link Control (LLC) Sublayer
• Media Access Control (MAC) Sublayer

The MAC address is used by the Media Access Control (MAC) sublayer.

The MAC is assigned to the Network Interface Card (NIC) of any device that can connect to the Internet. The vendor provides the number at the time of the device's manufacturer, and it's embedded in its NIC (hence the "burned in" description), which typically cannot be changed.

How a MAC Address differs from an IP Address

We need two addresses, the IP address and the MAC address, to facilitate communication between two networked devices. Both of these addresses identify a network device but do it differently. The MAC address identifies the device locally, while the IP address identifies it globally. The MAC address is only relevant to the Local Area Network (LAN) to which it's connected and isn't part of the data stream when the packets leave the device's network.

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This chart illustrates the differences between MAC addresses and IP addresses:

The Reason to Have Both an IP and a MAC Address

We’ve already established that a device needs an IP address so it can be identified across different networks. The MAC address identifies the device within the same network. So, if a user’s computer will never access the Internet, then theoretically, it wouldn’t need an IP address, but often does that happen? Try never.

So, a device needs the MAC address to establish its identity within an organization’s private network but needs an IP address to interact with other networks. Therefore, the device needs both to establish all required credentials regardless of the situation.

Why Should a MAC Address Be Unique in a LAN Network?

If a LAN has multiple devices with the same MAC address, the network won’t work.

For example, devices Alpha, Bravo, and Charlie are connected to a network via a switch. Their MAC addresses are 11100ACB68GC, 01100BDD64GB, and 11100ACB68GC, respectively. As you can see, the NICs of the Alpha and Charlie devices have the same MAC address. If Bravo transmits a data frame to the address 11100ACB68GC, the switch will fail to deliver it to the destination because there are two possible recipients of the data frame.

It looks like someone at the NIC manufacturer is going to lose their job!

So, to sum it up, if each device doesn’t have a unique identifier (the MAC address) that distinguishes it from all other devices on the network, the network breaks down.

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What is a MAC Address: The Format of a MAC Address

Remember, we can’t alter the MAC address; it’s hardcoded into the NIC when it’s manufactured. The MAC is globally unique, so two devices can’t have the same MAC address. Each device’s MAC is represented in a hexadecimal format on each device, like this: 00:0a:45:2e:52:28. It’s a 12-digit number and is 48 bits long, also called a 6-byte hexadecimal number. It’s split into six octets, and each octet has eight bits.

The first 24 bits (or three octets) are used as the Organization Unique Identifier (OUI), and 24 bits are vendor-specific and assigned to and burned into the NIC. For instance, here are the OUIs from a couple of popular vendors:

Cisco: CC:46:D6

Google: 3C:5A:B4

Hewlett Packard: 3C:D9:2B

OUIs are assigned to each vendor or organization by the IEEE Registration Authority Committee, so there’s no duplication.

There are three possible formats for MAC addresses:

• Hyphen-Hexadecimal notation: 00-1s-99-f1-d2-4f
• Colon-Hexadecimal notation: 00:1s:99:f1:d2:4f
• Period-Separated Hexadecimal notation: 001.s99.f1d.24f

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What is a MAC Address: Types of MAC Addresses

There are three kinds of MAC addresses available. They are:

• Unicast MAC address. This MAC address represents the specific NIC on the local network. The Unicast MAC address frame is transmitted only to the interface that’s assigned to a particular NIC, so it’s transmitted to only the single destination device.
• Multicast MAC address. This MAC address lets the source device transmit a data frame to more than one device or NIC.
• Broadcast MAC address. This MAC address represents every device within a given network. If a source device wants to send data to every device in a network, it can use the broadcast address as the destination’s MAC address.

How to Find the MAC Address of a Device

By now, you may be wondering how to find your device’s MAC address. If you have a Windows-based device, follow these steps:

• Press the Windows key or click Window Start
• You will get a search box. Type “cmd” to open your command prompt
• Press Enter. Then type “ipconfig/all command” at the prompt and press Enter
• You will get a screen with a lot of information displayed. Scroll down and look for the physical address. That’s your MAC address.

If you have a macOS system, follow these steps:

• Open the Apple Menu and click on System Preferences, or just choose the Apple icon
• Under system preferences → Select Network →
• That path opens a network box
• Select the Wi-Fi option found in the box. It then shows the Wi-Fi address or the Airport Address displays, and that’s where you will find your device’s MAC address

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What is MAC Cloning?

Sometimes, your Internet Service Provider (ISP) experiences a connectivity issue, usually when you try introducing a new MAC address to an existing network. For example, your ISP uses your device’s MAC address when the service is initially installed, but if you later place a router behind the network modem, the ISP won’t recognize the new address associated with the device’s WAN port.

So, you must either notify the vendor and register the new device’s MAC with them or clone the computer’s MAC address onto the new device’s WAN port.

Here’s how to accomplish the cloning:

• Click "Start" on the device that has the MAC address that you want to clone, then type "Cmd" in the search box found at the bottom of the menu, then press Enter.
• Type "ipconfig /all" in the command prompt window. Press Enter.
• Copy the MAC address located at the right of the Physical Address field, found under the Ethernet adapter field in the Command Prompt.
• Start the device that has the MAC address you want to change the type "network connections" into the search box located at the bottom of the menu. Then, click "View Network Connections."
• Right-click the "Wireless Network Adapter" or "Local Area Connection,” depending on which value you want to change, then select "Properties."
• Click the "Advanced" tab.
• Select "Network Address" from the list of properties.
• Click on the button to the left of the text box, then type the MAC address into the text box.
• Save your settings by clicking “OK.”
• Congratulations! You cloned!

What is a MAC Address: The Characteristics of a MAC Address

We already know that an Ethernet MAC address is a 48-bit binary value rendered as 12 hexadecimal digits with four bits per hexadecimal digit, but here are a few extra MAC address characteristics you should know.

• MAC addresses are in a flat structure, so they are not routable on the Internet
• Serial interfaces don’t use MAC addresses
• MAC addresses do not have a network or host portion
• MAC addresses deliver the frame to the destination device.

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