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Networking / LOCAL TOOL

MAC Address Tool

Convert MAC notations, read the assignment bits, and derive the EUI-64 and link-local address.

Runs locally — input is never uploaded
A MAC address in any notation, e.g. 00:1a:2b:3c:4d:5e
ResultReady when you are

WHAT IT DOES

Every notation, and the two bits that decide what the address means.

Enter a MAC address written any of the four ways it gets written and get the others, plus what its first byte says: whether a manufacturer assigned it or the device made it up, and whether it addresses one interface or a group. For a unicast address it also derives the EUI-64 interface identifier and the IPv6 link-local address that identifier produces.

Why use it?

Use it to normalize a hardware address from a log and distinguish address-format or assignment-bit facts from assumptions about a device.

How to use this tool

  1. Paste a MAC address in colon, hyphen, dotted, or compact notation and inspect it.
  2. For example, 02:00:00:00:00:01 has the locally administered bit set; do not infer a hardware manufacturer from that prefix.
  3. Copy the representation you need. A derived EUI-64 or link-local address is a calculation, not evidence that an interface actually uses that address.

Details and limitations

  • Colon, hyphen, Cisco's three groups of four, and no separators at all are all accepted and all shown. Sixteen hexadecimal digits are read as an EUI-64 rather than refused.
  • The second-least-significant bit of the first byte says whether the address was assigned by a manufacturer. When it is set the address is locally administered, which on a phone or a laptop means a randomised address generated for one network -- there is no vendor to look up, and this tool says so rather than reporting an unknown vendor.
  • The least-significant bit of the first byte says whether the address is a group rather than an interface. A multicast address is owned by no device, so no interface identifier is derived from it.
  • Addresses that a standard defines rather than a vendor owns are named: the broadcast address, the IPv4 and IPv6 multicast ranges, the IEEE 802.1 protocol group that carries spanning tree and LLDP, and Cisco's own protocol group.
  • The EUI-64 identifier is the MAC with ff:fe inserted in the middle and the universal/local bit flipped, and the link-local address is that identifier under fe80::/64. Modern systems use a random identifier instead, so that the address does not follow the machine between networks.

COMMON QUESTIONS

MAC Address Tool questions

Why can I not find the vendor for my phone's MAC address?
Because there is no vendor. Phones and laptops now use randomised addresses by default, generating a new one for each network they join, and such an address has the locally administered bit set to say so. Every lookup service will report it as unknown; the honest answer is that the address was never assigned to anybody. This tool reads that bit and tells you.
What is the difference between the notations?
None, beyond punctuation. Colons are what Linux and macOS print, hyphens are what Windows prints, and three groups of four separated by dots is Cisco's convention. All three describe the same six bytes, and this tool prints every form so a value can be pasted wherever it is needed.
How is an IPv6 link-local address derived from a MAC?
The six bytes are split in half, ff:fe is inserted between them to make eight, and the universal/local bit in the first byte is flipped. That 64-bit interface identifier goes under fe80::/64. This is why an interface can address a link with no configuration at all, and why privacy extensions were introduced: an address built this way identifies the hardware on every network it joins.
What does a MAC address starting with 01:00:5e mean?
It is an IPv4 multicast address rather than an interface. The low 23 bits of the IPv4 multicast group are copied into the low 23 bits of the MAC. IPv6 does the same thing under 33:33, taking the last four bytes of the IPv6 address, and ff:ff:ff:ff:ff:ff is the broadcast address that every station on the segment accepts.