Data Source and Methodology

Authoritative Source: IEEE 802 Standard for Local and Metropolitan Area Networks
Reference: IEEE Std 802-2014 (and subsequent revisions)
Link: IEEE 802 Standards Association

This tool generates 48-bit MAC addresses compliant with the IEEE 802 standard. A MAC address is composed of a 24-bit Organizationally Unique Identifier (OUI) and a 24-bit device identifier. All calculations and generation logic strictly adhere to the formatting and structural rules defined by this standard, including the correct setting of Universally (UAA) or Locally (LAA) administered bits.

The Formula Explained

A 48-bit MAC address is structured as 6 bytes (octets). The "formula" is this structure:

$$ \text{MAC Address} = \underbrace{B_1:B_2:B_3}_{\text{OUI (24 bits)}} : \underbrace{B_4:B_5:B_6}_{\text{NIC Specific (24 bits)}} $$

The first byte ($B_1$) contains two important control bits:

  1. I/G (Multicast) bit: The least significant bit (LSB). 0 for Unicast, 1 for Multicast. This generator always sets this to 0 (Unicast) to create valid host addresses.
  2. U/L (Administered) bit: The second-least significant bit.
    • Universally Administered (UAA): $B_1 = \text{xxxxxx0x}_2$. This is the "burned-in" address from a manufacturer.
    • Locally Administered (LAA): $B_1 = \text{xxxxxx1x}_2$. This is an address set by a local administrator, and it's the correct choice for generating virtual or "spoofed" addresses.

Glossary of Variables

OUI Prefix
The Organizationally Unique Identifier is the first 3 bytes (24 bits) of a MAC address, assigned by the IEEE to hardware manufacturers (e.g., Dell, Intel, VMware).
Device Identifier
The last 3 bytes (24 bits) of a MAC address, assigned by the manufacturer to be unique for each device within that OUI.
Universally Administered (UAA)
A globally unique address assigned by a manufacturer. The U/L bit in the first byte is set to 0.
Locally Administered (LAA)
An address that overrides the UAA, typically set by software or a network administrator. The U/L bit is set to 1. This is the recommended type for virtual machines to prevent conflicts.

How It Works: A Step-by-Step Example

Let's generate 5 random MAC addresses for a VMware virtual environment.

  1. Goal: Create 5 valid MAC addresses that look like they belong to a VMware virtual NIC.
  2. Step 1: Set Quantity. Enter 5 into the "Quantity" field.
  3. Step 2: Set OUI Prefix. VMware uses several OUIs. We'll use 00:50:56. Enter this into the "OUI Prefix" field.
  4. Step 3: Set Separator. We prefer standard colon notation, so we select "Colon".
  5. Step 4: Set Case. We select "Uppercase" for readability.
  6. Step 5: Click Generate.

The tool takes the fixed OUI 00:50:56 and appends 3 random bytes (e.g., A1:B2:C3) to create a list of valid, unique addresses like:

00:50:56:A1:B2:C3
00:50:56:4F:9E:01
00:50:56:D3:77:8B
...

Because a prefix was provided, the tool does not alter the U/L bit, as it assumes the provided OUI is already correct.

Frequently Asked Questions (FAQ)

What is a MAC address?

A Media Access Control (MAC) address is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a local network segment. It operates at the data link layer (Layer 2) of the OSI model.

Why would I need to generate a MAC address?

Common use cases include:

  • Virtualization: Assigning unique MAC addresses to virtual machines (VMs).
  • Network Testing: Simulating multiple devices on a network.
  • MAC Filtering: Bypassing network access control that restricts access based on MAC addresses.
  • Privacy: Obscuring your real hardware address on public Wi-Fi networks (though many modern OSes do this automatically).

What is the difference between UAA and LAA?

UAA (Universally Administered) is the "burned-in" address from the manufacturer, which is globally unique. LAA (Locally Administered) is an address set in software by a network administrator. When generating a random address, it is best practice to use LAA (by setting the U/L bit to 1) to ensure you don't accidentally conflict with a real, physical device on the network.

Is it legal to change (spoof) my MAC address?

In most jurisdictions, changing your MAC address for legitimate purposes (like virtualization or testing) is perfectly legal. However, using it for malicious activities (like impersonating another user to gain unauthorized access) is illegal and violates computer fraud and abuse laws.

Can a MAC address be tracked across the internet?

No. MAC addresses are only used for communication on the *local* network (e.g., your home Wi-Fi). When you access the internet, your router strips the MAC address and replaces it with its own. Your device's MAC address does not travel past your local router.

What is an OUI?

The Organizationally Unique Identifier (OUI) is the first 24 bits (3 bytes) of a MAC address. The IEEE assigns these blocks to manufacturers. For example, `00:1A:2B` might be assigned to Intel, and `00:50:56` to VMware. This allows you to identify the manufacturer of a device just by looking at its MAC address.

How many unique MAC addresses are there?

A MAC address is 48 bits long. This means there are $2^{48}$, or 281,474,976,710,656 (over 281 trillion), possible unique MAC addresses, making it extremely unlikely for two devices to ever have the same one by chance.

Tool developed by Ugo Candido.
Network protocols content verified by the CalcDomain Editorial Board.
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