About

A MAC (Media Access Control) address is a 48-bit identifier assigned to network interface controllers. It consists of 6 octets, where the first 3 form the OUI (Organizationally Unique Identifier) assigned by IEEE, and the last 3 are vendor-assigned. Misconfigured or duplicate MAC addresses on a LAN segment cause frame delivery failures, ARP table corruption, and intermittent connectivity that is notoriously difficult to diagnose. This generator produces cryptographically random addresses with correct bit-flag control for unicast/multicast and UAA/LAA fields, avoiding the common mistake of generating addresses with invalid administrative flags.

The tool supports vendor OUI prefixes from major manufacturers. Bit 0 of the first octet (b₀) determines unicast (0) vs. multicast (1). Bit 1 (b₁) determines universally administered (0) vs. locally administered (1). When testing virtual machines, containers, or network simulations, always use LAA addresses to avoid collisions with real hardware. Note: this tool generates syntactically valid addresses but cannot guarantee global uniqueness across physical networks.

Formulas

A MAC address is a 48-bit value partitioned into 6 octets. The generator produces random bytes and applies bitmask operations on the first octet to enforce administrative flags:

octet₀ = (octet₀ ∧ 0xFE) ∨ multicast_bit

octet₀ = (octet₀ ∧ 0xFD) ∨ (LAA_bit × 2)

Where multicast_bit ∈ {0, 1} controls bit 0 (least significant) of the first octet. LAA_bit ∈ {0, 1} controls bit 1. Masking with 0xFE (11111110₂) clears bit 0; masking with 0xFD (11111101₂) clears bit 1. The OR operation then sets the desired value. Full address format:

MAC = octet₀ : octet₁ : octet₂ : octet₃ : octet₄ : octet₅

Each octet_i is an unsigned integer in range [0, 255]. When a vendor OUI prefix is selected, octet_0..2 are fixed to the vendor values and only octet_3..5 are randomized. Randomness is sourced from crypto.getRandomValues, which provides a CSPRNG compliant with NIST SP 800-90A.

Reference Data

Vendor	OUI Prefix	Common Devices
Apple	A4:83:E7	iPhones, MacBooks, iPads
Intel	00:1B:21	Ethernet adapters, Wi-Fi modules
Samsung	00:16:32	Galaxy phones, Smart TVs
Cisco	00:1A:2F	Routers, switches, access points
Dell	00:14:22	Servers, workstations, laptops
Huawei	00:E0:FC	Routers, LTE modems, phones
Netgear	00:1E:2A	Home routers, switches, NAS
TP-Link	50:C7:BF	Wi-Fi routers, range extenders
Microsoft	00:50:F2	Surface, Xbox, Hyper-V virtual NICs
VMware	00:0C:29	Virtual machine NICs
Raspberry Pi	B8:27:EB	Raspberry Pi boards (pre-Pi 4)
Google	3C:5A:B4	Chromecast, Nest, Pixel
Amazon	74:C2:46	Echo, Fire TV, Kindle
Sony	00:04:1F	PlayStation, Bravia TVs
HP	00:1A:4B	ProLiant servers, printers
Lenovo	00:06:1B	ThinkPad, ThinkCentre
LG Electronics	00:1C:62	Smart TVs, phones
Broadcom	00:10:18	Embedded chipsets, NICs
Juniper	00:05:85	Enterprise routers, firewalls
Ubiquiti	04:18:D6	UniFi APs, EdgeRouters

Frequently Asked Questions

A Universally Administered Address (UAA) has bit 1 of the first octet set to 0, indicating the address was assigned by the manufacturer per IEEE registration. A Locally Administered Address (LAA) has bit 1 set to 1, meaning it was overridden by a network administrator or software. Virtual machines, containers, and test environments should always use LAA addresses to avoid conflicting with hardware-assigned UAA addresses on the same network segment.

Duplicate MAC addresses on the same Layer 2 broadcast domain cause ARP table instability. Switches will oscillate the port mapping for that address, resulting in frame loss for both devices. The probability of a random collision across 2⁴⁶ possible unicast LAA addresses is astronomically low for small networks, but when cloning VMs or containers, duplicate MACs are a frequent operational issue. Always regenerate addresses per instance.

Cisco IOS uses a dot-separated notation grouping 4 hex digits (2 octets) per segment: XXXX.XXXX.XXXX. This is purely a display convention. The underlying 48-bit value is identical to colon or hyphen notation. Cisco chose this format for compact display in CLI output. When configuring ACLs or port security, ensure you match the format your platform expects.

When bit 0 of the first octet is 1, the address is a multicast (group) address. Switches flood multicast frames to all ports in the VLAN unless IGMP snooping is enabled. Using a multicast source MAC address for a NIC is invalid per IEEE 802.3 and will cause unpredictable behavior. For device spoofing or VM assignment, always use unicast addresses (bit 0 = 0).

The Web Crypto API provides a cryptographically secure pseudorandom number generator (CSPRNG) seeded from OS entropy. For MAC address generation, this far exceeds requirements. The address space for unicast LAA is 2⁴⁶ (70.4 trillion) values. Even generating 1000 addresses, the birthday-problem collision probability is approximately 7 × 10⁻⁹. For non-cryptographic uniqueness purposes, this is more than adequate.

VMware uses 00:0C:29, 00:50:56, and 00:05:69. Microsoft Hyper-V uses 00:15:5D. Xen uses 00:16:3E. If you want a vendor-neutral approach, select LAA mode with no OUI prefix. This sets bit 1 to 1, which signals the address is locally assigned and avoids any association with a physical hardware vendor.