How to Use the Random MAC Generator Step by Step

How do you use the Random MAC Generator?

Open the Random MAC Generator, set "How many addresses?" to any value from 1 to 100, choose Unicast or Multicast, optionally pick a vendor OUI prefix, and the address list appears immediately — one uppercase, colon-separated MAC per line, ready to copy or download. There is no submit button and no signup step; the list updates as you change the inputs.

In practice that means four clicks at most. Leave the count at its default of 10, leave the type on Unicast, leave the prefix on "None — fully random," and you already have a usable batch of test fixtures. Swap the prefix to 52:54:00 and you have ten addresses that look like QEMU/KVM virtual NICs. Bump the count to 100 and you have a load-test dataset.

The generator runs in the browser and the built-in OUI list is hard-coded rather than queried from a lookup API, so the page does not need an account, an install or a network round-trip to produce output. That matters when you are pasting the same list into three different lab machines.

Setting the count, type and vendor prefix

The count field accepts 1–100 and defaults to 10, with quick-pick chips for 1, 10, 25 and 100. If you type something outside the range, the value is clamped and an inline hint tells you so — you will not silently get 0 addresses or a 500-line dump.

Address type is a two-way segmented control, Unicast or Multicast, and it decides one specific bit rather than the whole address (see the next section). Vendor OUI prefix is a dropdown of well-known prefixes: 00:50:56 and 00:0C:29 for VMware, 08:00:27 for VirtualBox, 52:54:00 for QEMU/KVM, 00:16:3E for Xen, B8:27:EB and DC:A6:32 for Raspberry Pi, plus 00:1B:63 and F0:18:98 for Apple. Choosing Custom prefix lets you type any three-octet hex value such as 02:1A:2B.

The output block stays Newline-separated on purpose so it drops straight into a config file or a spreadsheet column. Three actions sit next to it: Copy all, Download .txt and Regenerate. A short status line underneath confirms what was produced — count, type and prefix — and flags anything unusual, such as a prefix that had to be adjusted.

What does the I/G bit change in a MAC address?

A MAC address is 48 bits: a 24-bit OUI plus a 24-bit device portion, written as six colon-separated octets. Bit 0 of the first octet is the Individual/Group bit. Set it to 0 and the address is unicast, identifying a single interface; set it to 1 and the address is multicast, identifying a group. So 00:50:56:8F:1C:2A is unicast, while 01:00:5E and 33:33 prefixes are multicast.

That single bit is why some prefixes simply cannot be unicast. 01:00:5E and 33:33 both start with an odd first octet, so they are multicast by construction. If you pick a Custom prefix whose first octet is odd and ask for Unicast, the generator flips the bit to honour your requested type and says so in the generation note — check that line before you paste, because the prefix you see in the output may differ from the one you typed.

The neighbouring bit 1 is the U/L, or locally administered, flag. QEMU's 52:54:00 is an instructive example: 0x52 is 0101 0010, so bit 0 is 0 (unicast) and bit 1 is 1 (locally administered). Hypervisors lean on locally administered ranges precisely so their virtual NICs never collide with a real vendor's allocation. The IETF's RFC 7042 documents both bits in detail.

Pasting output into ACLs, DHCP and VM NICs

Because the output is one address per line with colons and uppercase hex, it fits most network tooling without reformatting. In a switch ACL or port-security list you can paste addresses directly after the matching keyword; in a DHCP reservation file you can pair each line with an IP and a hostname in a spreadsheet before exporting. Wi-Fi MAC filter allowlists and demo datasets take the raw block as-is.

For anything that needs the prefix to look coherent — a demo, a screenshot, a test fixture — pick one OUI and generate the whole batch from it. Ten addresses from 00:0C:29 read as one VMware fleet; ten addresses from random OUIs read as noise. If your test also needs unique per-object identifiers, the UUID v7 Generator covers that side of the fixture and pairs naturally with a MAC batch.

Two practical habits save time. First, download the .txt rather than copying, so you have a record of exactly which addresses went into which lab. Second, generate per environment instead of reusing one block everywhere — a duplicated MAC across two vSwitches is a confusing failure to debug later.

Where random MAC addresses are the wrong tool

The generator draws each address independently from the 24 bits of the device portion, so duplicates are possible in a batch. With a fixed OUI and 100 addresses, the birthday-problem chance of at least one repeat is roughly 4,950 pairings out of 16,777,216 values, about 0.03% — small, but not zero. If uniqueness is critical, sort the downloaded list and scan for repeats before you import it.

The bigger limitation is knowledge, not randomness. No generator can tell you which MAC addresses are already in use on your network, which are reserved by your hypervisor, or which belong to hardware sitting in the next rack. Random output is test data; it is not a reservation. The OUI dropdown is also a short hard-coded convenience list, not the full IEEE registry — for authoritative vendor lookups use the IEEE Registration Authority OUI database.

Finally, be deliberate about where you apply these values. Changing a MAC on equipment or a network you do not administer can break DHCP scopes, bypass filtering and violate acceptable-use policies, and as of 2026 most desktop and mobile operating systems randomise their own Wi-Fi MACs by default anyway. Use the output in labs, VMs, containers and test harnesses, and verify anything heading for production against your own inventory. Across OnlineFree.app's free online tools, every page follows the same rule: instant results, nothing to install, and no guarantee that the data is right for your specific environment.

References

• IEEE Registration Authority OUI database
• IETF RFC 7042 — IANA Considerations and IETF Protocol and Documentation Usage for IEEE 802 Parameters