{{ summaryTitle }}
{{ summaryValue }}

{{ summaryLine }}

Policy {{ resultsReady ? batch.policy_label : '—' }} Format {{ resultsReady ? batch.format_label : '—' }} Rows {{ resultsReady ? batch.generated_count : '—' }}
Local VM is the safest general fixture; vendor prefixes remain synthetic examples.
{{ prefixHelp }}
Choose local unicast for VM, container, documentation, and parser fixtures unless another flag pattern is the test.
Colon, hyphen, Cisco-dot, and compact hexadecimal notations are available.
Use a small batch for documentation and larger batches for controlled test fixtures.
rows
Choose the hexadecimal letter case expected by the receiving fixture or document.
Preserve exact vendor or protocol prefixes; enforce flags for policy-driven fixtures.
When enabled, every 48-bit value in the current batch must be distinct.
Leave blank for a fresh browser-local batch; add a seed for repeatable fixtures.
#MAC addressPlain hexTypeAdministrationCopy
{{ row.index }}{{ row.address }}{{ row.plain }}{{ row.type }}{{ row.administration }}
SignalValueMeaningCopy
{{ row.signal }}{{ row.value }}{{ row.meaning }}
MAC Address Details Lookup Inspect a MAC or EUI address with normalized forms and first-octet flags plus special-use checks and optional vendor assignment evidence.
Universally Unique Identifier (UUID) Generator Generate random, name-based or time-ordered UUIDs and inspect canonical form with version semantics, bit allocation and privacy tradeoffs.
Random Number Generator Generate random integers or decimals from a stepped range with secure or seeded draws, weighted profiles, exclusions, and repeat controls.
Password Strength Calculator Check a password against predictable patterns and attack scenarios, compare estimated crack times, and keep the candidate in your browser.

Two interfaces using the same MAC address on one network segment can make traffic reach the wrong place or disappear intermittently. That is why a generated address needs more than six plausible-looking hexadecimal bytes. Its address class, fixed prefix, and chance of colliding with another assignment all matter.

The common 48-bit form contains six octets. The two lowest-order bits of the first octet have special meaning. The individual/group bit distinguishes one-interface traffic from group traffic, while the universal/local bit distinguishes an address administered under a global assignment from one managed locally. For virtual machines, containers, test fixtures, and private lab inventories, a locally administered individual address is usually the appropriate starting point.

First-octet flags Meaning Suitable context
I/G 0, U/L 1 Individual, locally administered VMs, containers, private labs, and synthetic fixtures
I/G 0, U/L 0 Individual, universally administered A real assigned prefix, or a clearly labeled vendor-shaped example
I/G 1 Group address Multicast or broadcast behavior, not a normal interface identity

An Organizationally Unique Identifier (OUI) is an IEEE-assigned prefix, not a decorative vendor label. Copying a familiar OUI into test data does not grant authority to assign real global addresses beneath it. Preserving that prefix can be useful for parser tests and documentation, but local-unicast space is safer when the address will actually be attached to a lab interface.

Colon, hyphen, Cisco-dot, and plain hexadecimal forms are only notations for the same 48 bits. Reformatting an address does not change its flags or make it unique. A generated batch can prevent duplicates within that batch, but only the administrator of the destination network can check it against addresses already in use.

How to Use This Tool:

Choose the address policy before choosing how the bytes should look.

  1. Select a preset or choose custom settings. Local VM batch is the general-purpose choice for controlled virtual networks.
  2. Enter a Prefix / OUI as zero to six complete hexadecimal bytes, then choose Address flags. Use Preserve supplied first octet when an exact protocol or vendor-shaped prefix matters; otherwise enforce the selected flags.
  3. Set Quantity from 1 to 500 and keep Unique within batch enabled unless repeated values are part of the test. If the requested count exceeds the remaining address space, shorten the prefix or reduce the count.
  4. Add a Deterministic seed for a repeatable fixture, or leave it blank for a fresh batch. Review the address class and any prefix-adjustment note before assigning the values.

Interpreting Results:

The first address is a quick preview, while the full batch shows the values that belong in the fixture or lab configuration. Check three facts before use:

  • The address class should match the job. A normal VM interface should read Unicast / individual and Locally administered.
  • The run audit should show enough remaining possibilities for the requested unique batch. A small capacity means the prefix or enforced bits leave little room.
  • A clean batch proves only that values do not repeat within this generation run. It does not prove that another host, hypervisor, reservation, or static configuration is not already using one.

Technical Details:

An EUI-48 address is a 48-bit value. In the first transmitted octet, bit 0 is the individual/group flag and bit 1 is the universal/local flag. Enforcing a policy may therefore replace those two bits even when the first byte came from a supplied prefix; preservation leaves the supplied first octet unchanged.

Rule Core

Policy I/G bit U/L bit Result
Local unicast01Individual address in local administration space
Universal unicast00Individual address shaped like a global assignment
Local multicast11Locally administered group address
Universal multicast10Universally administered group address
Random flagsRandomRandomAll four flag combinations may appear

Prefix text is normalized to complete bytes. Colons, hyphens, dots, and spaces are accepted as separators, but a half-byte prefix is rejected. Up to six fixed bytes may be supplied.

Formula Core

The unique capacity is the number of combinations left after fixed prefix bits and enforced flag bits are removed. If r bits remain generated, capacity is:

C = 2r

For example, a two-byte prefix with an enforced non-random flag policy leaves 32 generated bits, so the batch space contains 232, or 4,294,967,296, possible values. A preserved three-byte prefix leaves 24 generated bits and 16,777,216 possibilities. The generator rejects a unique request larger than the available capacity.

Generation and notation

A nonblank seed produces a deterministic byte stream for the same prefix, flag policy, and first-octet handling. A blank seed uses a fresh browser-local run value. Duplicate 48-bit values are discarded when within-batch uniqueness is enabled. This repeatability is intended for fixtures and demonstrations; it is not a cryptographic or globally coordinated address-allocation service.

Formatting happens after the bytes are chosen. For example, 02:42:AC:11:00:02, 02-42-AC-11-00-02, 0242.AC11.0002, and 0242AC110002 represent the same address.

Privacy and Safe Use:

Generation stays in the browser, and a seed is useful only as a reproducibility label, not as a secret. Generated values should remain in controlled labs, tests, or clearly synthetic documentation unless a network administrator has checked them against the actual segment. MAC addresses observed on real networks can also identify or track interfaces, so avoid publishing captured production addresses merely because the format looks harmless.

References: