Test Data · Throwaway Addresses

MAC Address Generator

Addresses for a lab network, a virtual machine or a row of seeded test data. Nothing here is registered to anybody, which is the whole point — and also why none of it belongs on hardware you intend to ship.

Target Model

Quantity

When you need one

When a made-up address is the right answer

Anything that speaks Ethernet needs an address before it will talk: a virtual machine, a container bridge, a bench rig, a fixture row in a test database. Typed out by hand, the result is usually the wrong length, or carries a character that is not hexadecimal, and it fails the first validator it meets.

Two bits inside the first octet decide how an address behaves, and getting them wrong is what makes test data misbehave. The lowest bit separates a single interface from a group. The next one up marks the address as locally administered — nobody registered it with the IEEE — which is what keeps invented addresses clear of blocks real manufacturers own.

Where these end up

Lab networks

Stand in for kit you do not have

Virtual machines

One address per guest interface

Seeded fixtures

Fill a test table with plausible rows

Bench hardware

Mock a sensor before it exists

FAQ

Frequently Asked Questions

Can I put one of these on real hardware?

No. On a live network an invented address is a bet that nothing else is using it, and a clash drops both interfaces off the network while looking exactly like a faulty cable. Keep them inside test environments, where a collision costs nothing and is easy to spot.

Unicast or multicast — what is the difference?

The least significant bit of the first octet decides it. Zero means unicast: one interface. One means multicast: a group of them. Standing in for a single device means unicast, and a stray bit here is a common reason a mocked device never appears on the network.

What makes an address locally administered?

The second least significant bit of the first octet is set to 1, which says the address was assigned locally rather than drawn from a block the IEEE sold to a manufacturer. In hexadecimal the tell is the second character: 2, 6, A or E. Phones use this same range for the randomised Wi-Fi addresses they show to each network they join.