What a MAC Address Actually Encodes
A 48-bit MAC address is not an opaque serial number. The first three bytes are the OUI, the block the IEEE assigned to a manufacturer. Two bits of the very first byte carry meaning of their own: one marks the address as locally administered rather than IEEE assigned, and the other marks it as multicast rather than unicast. Everything this tool reports from those bits is exact, because it is read from the address itself. Vendor naming is different: the IEEE registry holds tens of thousands of assignments, so the table packaged in this page covers common consumer, network and virtualization hardware rather than all of it, and the output says which case you are in instead of implying a full registry lookup. The tool also derives the modified EUI-64 form defined in RFC 4291, which is how a host builds an IPv6 link-local address from its hardware address.
How to Use the MAC Address Lookup Tool
- 1Paste a MAC address in any common style: colons, hyphens, Cisco dotted quads, or bare hexadecimal.
- 2Read the normalized, dashed and Cisco forms when you need to match the format another tool expects.
- 3Check the administration and cast lines to see whether the address is IEEE assigned or locally administered, and unicast or multicast.
- 4Use the vendor line as a hint, and note when the result says the address is outside this page\u2019s curated table.
- 5Copy the derived IPv6 link-local address when you are working out how a host will autoconfigure.
Common MAC Address Lookup Use Cases
Identify an unknown device on your network
Match an address seen in a DHCP lease or ARP table against common vendor prefixes before escalating an investigation.
Explain a phone that reports no vendor
Confirm the address is locally administered, which is how modern phones randomize MAC addresses per network for privacy.
Predict an IPv6 link-local address
Derive the modified EUI-64 interface identifier a host forms from its hardware address when it autoconfigures.
Reformat addresses between tools
Convert between colon, hyphen and Cisco dotted notation so captures, switch output and spreadsheets can be compared.
Frequently asked questions
Why does the vendor field say the address is not in the curated table?
Because it is not, and the tool will not guess. The IEEE registry contains tens of thousands of assignments and shipping all of them would make the page far heavier for a lookup most visitors do once. Every other field is derived from the address itself and remains exact, so an unlisted vendor never means the address is invalid.
Why do phones and laptops often show no vendor at all?
They deliberately use a locally administered address. iOS, Android, Windows and macOS all randomize the MAC address per network so that the same device cannot be tracked between Wi-Fi networks. Such an address is generated by the device, so no manufacturer is registered for it, and the tool points this out when it sees the local bit set.
What is the modified EUI-64 form for?
It is the RFC 4291 rule for turning a 48-bit MAC into a 64-bit IPv6 interface identifier: split the address in half, insert FFFE in the middle, and flip the universal/local bit. A host that uses it forms the link-local address shown here, which is useful when predicting or verifying IPv6 autoconfiguration.
Is the lookup done against an external service?
No. Normalization, bit analysis and vendor matching all run in the browser against a table packaged in the page, so the tool works offline and no address you paste is sent anywhere.