MAC Address Generator
Locally Administered, Safe to Assign

How to Generate a MAC Address That Actually Works

To generate a MAC address you need six bytes of hexadecimal. That part is easy, and it is all most tools do. The part that matters is that two of the forty-eight bits are not free for you to pick, and if you let chance decide them you will produce an address that either cannot be assigned to anything or quietly claims to be somebody else's hardware.

So the honest answer to how to generate MAC address values properly is three steps rather than one:

1. Decide the class first. If you are assigning the address to a virtual machine, a container or a test interface, you want a locally administered unicast address. That is the range set aside for exactly this purpose.
2. Fix the first byte to match. Locally administered and unicast means the second hex digit must be 2, 6, A or E. Nothing else will do, and the tool above does this before it randomises anything else.
3. Fill the remaining bits randomly, then check for collisions. Forty bits is plenty of room, but if you are producing a batch they still need to be unique within it.

The generator handles all three. Press Generate and you get a valid address; the panel underneath tells you which class you got and whether it is safe to assign, so you are not taking the result on trust. Use it to generate MAC address values one at a time, or to generate MAC addresses fifty at a time for a lab build.

Doing it by hand

You do not need a free MAC address generator for a single address. To generate a random MAC address by hand, take any six random bytes, then set the first byte so the second hex digit is 2, 6, A or E. 3A:1F:B2:44:90:C7 is valid. 3B:1F:B2:44:90:C7 is not, because B is odd and an odd second digit means multicast.

Where a unicast MAC address generator earns its place is volume and consistency: fifty addresses for a lab, all unique, all in the right class, in the format your config file wants, without you checking fifty first bytes by eye.

Why Three in Four Random MAC Addresses Are Unusable

Almost every random MAC address generator online rolls forty-eight random bits and prints the result. We measured what that produces over a hundred thousand samples:

Three out of four results are wrong for the job, and none of those sites mentions it. Assign a multicast address to an interface and the interface will not come up, or it will come up and traffic will behave strangely, and nothing will tell you why. The address looks perfectly normal.

Why the second quarter matters less, but still matters

A universally administered address will almost always work. The objection is not that it breaks; it is that you have taken an unnecessary bet. Every one of those addresses sits inside a block that the IEEE assigned to a real company, and somewhere there may be shipped hardware carrying it. On your home lab, the odds are negligible. On a large flat network, on a segment you do not fully control, or in a DHCP reservation you will still be relying on in three years, it is a bet with no upside.

The locally administered range exists precisely so nobody has to take it. It costs nothing to stay inside it.

Unicast, Multicast, and the Two Bits That Decide Everything

A MAC address is 48 bits — six octets, twelve hexadecimal characters. Forty-six of them are yours to do as you like with. The two that are not both live in the first octet, and between them they decide what kind of address you have made.

• The I/G bit (bit 0, the least significant bit of the first octet). Clear means unicast — one interface. Set means multicast — a group of interfaces.
• The U/L bit (bit 1). Clear means universally administered, assigned by the IEEE to a manufacturer. Set means locally administered — made up by software or by you.

Because both bits sit in the low half of the first octet, they are visible in the second hex character of the address. You never have to work in binary to read them:

So a valid unicast MAC address is any address whose second hex digit is even. A unicast MAC address example you can safely assign would be 4E:2B:91:0A:7C:D3 — second digit E, locally administered, unicast. Compare it with 4F:2B:91:0A:7C:D3, one character different, which is multicast and will not work as an interface address.

The MAC address generator unicast option above is the default for this reason — if you searched for a random MAC address generator unicast mode specifically, that is what you already have. You can switch to multicast deliberately, and the tool will tell you what you have made, but you will not get one by accident.

Broadcast is the extreme case of multicast: FF:FF:FF:FF:FF:FF, every bit set, delivered to everything on the segment. Our guide to broadcast addresses in networking covers where that fits at Layer 2 and Layer 3.

Generating MAC Addresses for Virtual Machines

This is what most people actually came for. Every hypervisor will hand a guest an address automatically, and most of the time that is fine. You need a static MAC address of your own when you want it to survive a rebuild, when a licence is pinned to it, when a DHCP reservation depends on it, or when you are provisioning machines from a script and want the addresses decided in advance.

Each platform has its own registered vendor OUI prefix, and the generator's presets apply them:

The VMware range that stops VMs booting

If you take one thing from this page, take this. A VMware MAC address generator that just bolts random bytes onto 00:50:56 will eventually hand you an address VMware refuses. This is the detail that makes a MAC address generator VMware administrators can actually rely on different from a generic one.

VMware splits its own OUI. Addresses from 00:50:56:80:00:00 to 00:50:56:BF:FF:FF are what vCenter allocates for itself. The window left for manual assignment is 00:50:56:00:00:00 to 00:50:56:3F:FF:FF — the fourth byte must be 3F or lower. Set an address outside it and the VM can refuse to power on, with an error that says nothing about MAC ranges.

The VMware preset above caps that fourth byte. We generated five hundred addresses through it and checked every one; the highest fourth byte produced was 3F. No other generator we examined applies this constraint.

Proxmox, KVM and containers

A Proxmox MAC address generator has an easier job, because QEMU's 52:54:00 prefix is already locally administered. Pick the QEMU preset and paste the result into the VM's network device, or use the qm set line the tool produces. The same address works for a plain libvirt domain or a docker run --mac-address flag — the config snippets under your results cover Proxmox, VMware's .vmx, VirtualBox, libvirt XML, Linux ip link and Docker.

Two things that catch people out. Cloning a VM copies its MAC address, so a clone that keeps the original address will fight with its parent the moment both are running. And a DHCP reservation is tied to the address, so changing the MAC silently invalidates the reservation and the guest starts taking pool addresses instead.

Once a machine is running, you can confirm what you assigned actually landed by checking the address in the MAC address lookup. A locally administered address comes back as exactly that, with no vendor, which is the correct answer rather than a failed search.

Bulk Generation for Testing, Labs and Sample Data

The other half of the demand is test data. If you are building anything that accepts a MAC address — an inventory system, a NAC policy engine, a DHCP server, a form with a validation rule — you need realistic input, and you need more than one.

A bulk MAC address generator is worth having for a simple reason: uniqueness. Generate fifty by hand and you will not check them against each other. This tool produces up to 500 unique addresses per batch and guarantees no duplicates within it, including inside a constrained range like the VMware window where the space to draw from is much smaller.

What people use a MAC address for testing:

• Seeding a database with plausible device records. A sample MAC address that looks like the real thing without belonging to anything is exactly what MAC address test data should be.
• Validation testing. Generate valid addresses, then break them deliberately — drop an octet, add one, swap in a non-hex character — and confirm your parser rejects what it should.
• Network simulation and load testing, where a switch or controller needs to see many distinct Layer 2 endpoints.
• Lab and demo environments, where fifty VMs need addresses decided before any of them exist.
• Documentation and screenshots, where you want a realistic address that is definitely not a real customer's.

Fake, dummy, alternate, random — all the same thing

This corner of the internet has collected an unusual number of names for one idea. A fake MAC address generator, a dummy MAC address, an alternate MAC address generator, a MAC address maker, a MAC address randomizer, a MAC address creator — in practice these all mean the same thing: an address produced by software rather than burned into a network interface controller at the factory.

The same goes for the word order people type. MAC address generate online, MAC address online generator, generator MAC address — all of them land on the same job, and the phrase you happened to use makes no difference to what you get. Whichever term brought you here, the tool above is it, and the advice does not change: for anything you are assigning, use the locally administered unicast option. The only time to reach for a universally administered address is when a test fixture genuinely needs to look like shipped hardware, and even then it is worth knowing that is what you are doing.

Output Formats and Exporting Your Results

The same forty-eight bits get written four different ways depending on who is reading them, and pasting the wrong one into a config file is a genuinely common way to waste twenty minutes. The MAC address format selector covers all four:

Case is a separate axis. Linux tooling generally writes lowercase, Windows and Cisco generally uppercase, and while nothing cares functionally, a config file that mixes both is harder to diff. The uppercase and lowercase switch is there so you can match whatever you are pasting into.

Getting them out of the browser

Every address has its own copy button, and there are two batch buttons above the results. Copy all gives you plain text, one address per line, which is what you want for a script or a config file. Copy as CSV adds a header row and three extra columns — administration, cast, and whether the address is safe to assign — which is what you want for a spreadsheet or a ticket.

Every setting also lives in the URL. Generate a batch with a VMware preset in lowercase hyphen notation and the shareable link reproduces exactly that, so a runbook can link to the settings rather than describing them.

Alternate MAC Addresses on Consoles and Routers

Two pieces of consumer hardware expose this setting directly, which is why a lot of people looking for an alternate MAC address generator are not running virtual machines at all.

Xbox

Xbox consoles have a network option literally called Alternate MAC Address, under Network settings, Advanced settings. It lets the console present an address other than its built-in one, and Microsoft put it there mainly to work around networks that behave badly with the console's own address — some hotel, campus and captive-portal networks among them.

If you are filling that field, the same rules apply as everywhere else on this page. The console wants twelve hexadecimal characters with no separators, and a locally administered unicast address is the correct kind — second hex digit 2, 6, A or E. Generate one above, pick the no separator format, and paste. If the console rejects it or the network still fails, clearing the field returns it to the factory address.

An Xbox MAC address generator is not really a separate thing; it is this tool with the separator turned off. The same goes for older consoles — a Wii MAC address generator is the same twelve characters in the same range.

Routers and MAC cloning

Consumer routers have the same feature under a different name. MAC cloning lets the router present a chosen address on its WAN interface, and it exists because some ISPs tie your service or your public IP to the address they first saw. Our guide to changing your router's IP address covers where cloning fits into that.

A router MAC address generator is, again, this tool. What differs is the advice: on a WAN interface facing your ISP, think before you change anything, because a service tied to the old address may stop working until the ISP's records catch up.

Changing an address on a computer

Operating systems let you override the hardware address at the driver level. On Linux it is two ip link commands, and the exact lines are in the config snippets under your results. On Windows it is an adapter property or a registry value, which is what a MAC address changer utility edits for you; on macOS, ifconfig, though recent versions have tightened this considerably.

People call this MAC address spoofing, and the word carries more menace than it deserves. Your phone already does it: MAC address randomization is on by default in modern iOS and Android, and Windows calls the same feature Random Hardware Addresses. It exists so a shop with Wi-Fi cannot log the same identifier on Tuesday and Friday and know it is the same person. Generating an address for your own machine is the same operation your phone performs every time it sees a new network.

What it does not do is make you anonymous. A MAC address never leaves the local network segment, so it was never visible to the websites you visit in the first place. MAC addresses and IP addresses do different jobs at different layers, and changing one has no effect on the other.

Generating a MAC Address in Code

If you need this inside a test suite or a provisioning script, you do not want a web page. The logic is four lines in any language: get six random bytes, force the first one into the locally administered unicast range, format.

The mask is the only part worth getting right. byte | 0x02 sets the U/L bit; & 0xFE clears the I/G bit. Together they guarantee the second hex digit lands on 2, 6, A or E.

Python

If you want a random MAC address generator Python can run inside a test suite, this is the whole of it:

import secrets

def random_mac():
    b = bytearray(secrets.token_bytes(6))
    b[0] = (b[0] | 0x02) & 0xFE      # locally administered, unicast
    return ':'.join(f'{x:02X}' for x in b)

C#

The same logic as a C# random MAC address generator:

using System.Security.Cryptography;

static string RandomMac() {
    var b = RandomNumberGenerator.GetBytes(6);
    b[0] = (byte)((b[0] | 0x02) & 0xFE);
    return string.Join(":", b.Select(x => x.ToString("X2")));
}

C

unsigned char mac[6];
getrandom(mac, 6, 0);
mac[0] = (mac[0] | 0x02) & 0xFE;
printf("%02X:%02X:%02X:%02X:%02X:%02X",
       mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);

Shell

printf '%02X' $(( (RANDOM % 256 | 2) & 254 ))
openssl rand -hex 5 | sed 's/\(..\)/:\1/g'

Two notes. Use a cryptographic source — secrets, RandomNumberGenerator, getrandom — rather than a seeded pseudo-random generator. Not because a test MAC needs cryptographic strength, but because a per-process seed produces visible patterns across runs, and these addresses end up in DHCP reservations that outlive the script. The tool above uses PHP's random_int() for the same reason.

And if you are generating for one specific hypervisor, prepend its prefix and randomise only the remaining bytes — remembering the VMware fourth-byte cap if that is your platform.

Duplicate MAC Addresses and What Actually Happens

MAC addresses are supposed to be unique on a segment. When two are not, the failure is memorable, because nothing announces it.

A switch keeps a table mapping addresses to ports. Give it two devices with the same address and the entry flaps between ports as each one transmits, so frames go to whichever device spoke most recently. The symptom is a connection that works for a few seconds, dies, works again — on both machines, alternately. Switches often log this as MAC flapping; most people just see intermittent networking.

A duplicate MAC address most often comes from one of three places:

• A cloned VM that kept its parent's address. Easily the commonest cause.
• A restored snapshot or backup running alongside the original.
• Hand-typed addresses in a provisioning script where someone incremented the wrong octet.

This is why the generator guarantees uniqueness within a batch rather than just producing addresses. Fifty random addresses drawn independently have a small but real chance of collision; fifty drawn from a constrained range like the VMware window have a considerably larger one. Every batch here is checked before it is shown to you.

To find an existing conflict, look at your switch's address table or your router's client list for the same address on two ports, and use arp -a on a nearby machine to see what the local ARP cache currently believes. A MAC address conflict and an IP address conflict produce similar symptoms and get confused constantly — our guide to resolving IP address conflicts covers the Layer 3 version, which is far more common.

How likely is an accidental collision? The locally administered unicast space holds 2⁴⁶ addresses, about seventy trillion. Randomly picking two identical ones is not a practical concern. Copying one by hand, or cloning a VM, is.

Frequently asked questions about generating MAC addresses