MAC Address Explained: Its Purpose and How to Spoof One

The MAC address is a critical element of networking, and you'll learn all about it in this post. However, the first thing to remember is that a MAC address differs from an IP address, although the two coexist nicely. You can even say one depends on the other.

That said, it's a good idea to check out my explainer on the IP address before (or after) this post. You might want to do that anyway.

Dong's note: I first published this post on March 1, 2019, and updated it on January August 23, 2024, to include additional relevant information.

What is a MAC address?

MAC stands for media access control. A MAC address—I'll call it MAC from now on—is a unique identifier to control the access of a network interface controller (NIC), which is often known as a network adapter.

Your device—be it a computer, a tablet, or a phone—can connect to the Internet because it has a NIC. This NIC is available as a Wi-Fi receiver (such as the Intel BE200,) an Ethernet adapter (wired), or a cellular modem.

An actual device, like a phone or a computer, only has a MAC address when it has a network adapter. If the device has more than one adapter, each will have its own MAC address.

A MAC address consists of six groups, called octets, of two hexadecimal numbers— 0 to 9 and A to F—separated by colons, hyphens, or nothing. That said, here is a MAC address as you'd see on a Windows computer:

D4-FB-6A-7C-31-B4 

This same address can also appear as d4:fb:6a:7c:31:b4 or D4FB6A7C31B4, depending on what platform or application you use to view it.

(This is a random address I made up for this post. If it belongs to an actual device, that's just a coincidence.)

As you might have noticed, MAC is not case-sensitive but tends to appear in all lower or upper cases. Generally, when you alter a digit or letter, you'll get a new MAC.

Things to keep in mind about MAC

Here are some interesting facts about the MAC address.

• Every network adapter must have a MAC. (The MAC address of a device, such as a phone or a computer, is that of its network adapter.)
• The MAC address can be called with different names. Here are a few examples: Physical address, basic service set identifier (BSSID), Ethernet hardware address (EHA), hardware address, or adapter address.
• A MAC is unique and permanent. It's embedded in each networking adapter by the manufacturer—the MACs of a company often share the first three numbers. It's like the vehicle identification number (VIN) of a car. (Take "permanent" with a grain of salt because, just like a VIN, it's susceptible to manipulation. More below.)
• Eventually, we'll run out of MAC addressing space. But considering this is a 48-bit scheme with a total of 281,474,976,710,656—that's 281 trillion and then some hundred billion more—possible addresses, it's safe to say many things more consequential, like humanity or hopefully just the need for the MAC itself, would expire before we have to worry about a MAC shortage. That's not to mention it's OK to use the same (virtual) MAC on two devices as long as they are not part of the same local network—more below.
• MAC addresses are allocated in large groups to hardware vendors. For this reason, connected network devices are often identified within the network as the name of the vendor—such as Dell, Cisco, Hon Hai, Netgear, etc.—instead of their MAC addresses or the names you give them. This is purely a matter of identity.

Generally, a device has its MAC on its label. It's not a secret; everyone can see it. Again, it's like the VIN of a car—it must be visible. However, once the device is yours, it's a good idea to keep this address secure. You'll know why by the end of this post.

Usage: MAC address vs. IP address

If MAC is the VIN of a car, then the IP address is the license plate. Both are used to identify a car, but at different levels and purposes. Specifically, you can't register your vehicle (and get a new license plate) if it doesn't have a VIN.

The use of a MAC address

A DHCP server (like your router) uses a MAC address to assign an IP address to a network adapter. Without MAC, an adapter can't get an IP address. Without an IP address, the device can't connect at all.

You can also use the MAC to reserve a particular IP address for an adapter within a local network. When this happens within the network, the device will get the same IP address each time it connects. This IP reservation feature is necessary for advanced network applications.

Conversely, you can also use MAC to deny (or explicitly allow) access to an adapter via MAC filtering, a kind of security feature. "Kind of" because it's not absolutely secure since you can actually "change" this address, as shown below.

For the most part, though, a MAC address is permanent when you don't do anything. Consequently, if someone knows your device's MAC (like your phone's), they can potentially keep track of you—both at local (LAN) and Internet (WAN) levels.

For this reason, by default, modern mobile devices automatically use a temporary random "virtual" (or "private") MAC address when they connect to a new or public Wi-Fi network. That's also one of the reasons why, now and then, you might want to change your device's MAC.

Reasons you might want to change your MAC

Take "change" with a loose meaning of the word. It's more of a spoofing than changing since this is only temporary at the software level. Specifically, you can only make a device appear to a third party with a virtual MAC address. Its actual MAC is always the same, only disguised by another.

Here are a few occasions where you might want to change your device's MAC.

• You want to re-use an already-approved MAC address on a new device—this is why many routers have a "MAC clone" feature. (By the way, in this case, on the reverse, if you change the MAC of an approved device, it will be disconnected.)
• You know your computer has been blocked or restricted from a network and want to sneak through.
• You're about to join a new network—like a public Wi-Fi—and don't want folks to know your device's real MAC.

And, finally, you don't need any reason. You can change the MAC for the hell of it because you can. But before you can do that, you need to know what your device's MAC is.

How to figure out your device’s MAC

Depending on the device type, there are many ways to find out a device's MAC address. For example, on a router or a modem, the address is generally on the underside of the hardware itself. Just flip it up and take a close look.

But most of the time, we need to figure this out via software, like the device's operating system. So, in a mobile device (like a phone), this tends to be in the "About Device" area.

You can find out about the MAC on computers the way you find out your current IP address—in the ipconfig command, it's the physical address.

Since MAC and IP are closely related, the two are almost always stored next to each other. In other words, if you see the IP, chances are the MAC is around.

How to change a device’s MAC address

Now that you know what a MAC is and where to locate it let's find out how you can (temporarily) change it. Unlike a VIN, it's not illegal to alter your device's MAC address. That's partly because you cannot permanently change a device's MAC address anyway. What you can do is disguise a NIC's actual MAC address as another using software.

This change is temporary. When you reset (or reinstall) the application, move the NIC to a different device, or even restart the device, its original MAC address will return.

Again, keep in mind the limited sense of the word "change" in this case. I'd say "MAC spoofing" is a more accurate choice of expression.

There are many different types of networking devices, some of which you can change the MAC address, others you can't. Generally, that's universally possible with a router or a computer. And that's probably all we'd need to do anyway.

How to change the MAC address of a router

It's only possible to change a router's MAC address if the router has the MAC Clone feature—most routers do.

In this case, all you have to do is log into the router's web interface, navigate to the WAN (Internet) setting area, and choose to enter a new MAC address—whichever you want as long as it fits the format.

Or you can clone the MAC of the computer you're using. After that, apply the change, and the router will carry that MAC address (when working with a third party) until you reset it to default factory settings.

How to change the MAC address of a Windows computer

There are many ways to change the MAC on a Windows computer. The following is the easiest way. You need to use an account with the administrator's privilege.

1. Click on the Start button, and type in ncpa.cpl then press Enter to call up the Network Connections window.
2. Right-click on the network adapter you want to work with and choose Properties. The Properties window of the connection will appear.
3. Click on Configure button, then on the Advanced tab.
4. Navigate to the "Network Address" (or "Locally Administered Address") entry.
5. Change the Value to a MAC address of your liking. It needs to be entered without any dash or colon, like this: D4FB6A7C31B4, then hit OK. If the new address doesn't work out, enter a new one until it does.

Again, there are complicated rules to form a MAC, but it's faster to start with a known valid one and then change a letter or number randomly until it creates a new MAC.

That's it. Restart your computer, and your new address will appear. To undo this, repeat steps 1 to 4, then choose Not Present before clicking OK. Also, if you reinstall Windows from scratch, the real MAC will be restored.

How to change the MAC address of a Mac computer

Again, there are a few different ways to change MAC on an Apple computer, but the following is the most convenient. Note that you need to log in to a Mac with an admin account for this to work.

1. Determine the NIC you're working with: This is called the interface name in the Apple world. If the computer has just one network adapter (all Wi-Fi-only computers are like that), then the interface name is always en0 (that's en—short for Ethernet—and zero). But if the machine has another NIC, its interface name will be en1, and so on. Determine which one's MAC you want to change.
2. Make sure the NIC is not being used: If this is an Ethernet NIC, disconnect the network cable. If it's a Wi-Fi adapter, press and hold the Option key on the keyboard, then click on the Wi-Fi icon (top right corner), then on Disconnect from the current Wi-Fi network. Do not disable (turn off) the adapter!
3. Call up Terminal: Use Spotlight (Command + Space bar) and then search for "Terminal". When you find it, click on it. The Terminal program will run.
4. Execute the MAC change command as shown below.

Assuming you want to use our example MAC address above—that's d4:fb:6a:7c:31:b4—and the NIC's interface name is en0.

Now copy and paste the following command into Terminal, then press Enter (enter your account's password, then press Enter again, if prompted):

sudo ifconfig en0 ether d4:fb:6a:7c:31:b4

(Clearly, d4:fb:6a:7c:31:b4 is the new MAC that you want to use. Replace it with one of your likings.)

Alternatively, you can use the following command to create a random MAC address:

openssl rand -hex 6 | sed 's/(..)/1:/g; s/.$//' | xargs sudo ifconfig en0 ether

And that's it. From this moment on, your NIC will have a new MAC address. When you restart the computer, the NIC's original MAC will return. To make the change persistent, you can write a startup script using the command above.

By the way, if you want to test if the new MAC is in effect, use this command:

ifconfig en0 | grep ether

It will show the current MAC address the adapter is using.

The takeaway

And that's all there is to know about the MAC address. You won't need to worry about it most of the time, but sometimes, knowing how to change your MAC can come in handy in handling some special situations. At the very least, it makes you feel like you're in control.

By the way, considering the vast number of MAC addresses, it's virtually impossible to have two devices sharing one MAC address in the same local network via randomizing.

But you can do that on purpose. In this case, both devices will get the same IP address, or neither will get one. Either case is no good. Generally, the result is that, at best, only one of the two can get connected, and most of the time, neither can. So, pick another MAC address for one of them or let the system handle the randomizing automatically.