How the EUI-64 Process Converts a 48-Bit MAC to a 64-Bit IPv6 Address
EUI-64 generation derives a 64-bit interface identifier from a 48-bit MAC address by inserting ff:fe between its first and last three bytes, then inverting the universal/local bit. The complete IPv6 address is still 128 bits: this tool combines the resulting identifier with a link-local prefix to form a candidate fe80:: address. It does not configure your interface or discover its actual address. Colon, hyphen, Cisco dot, and raw hexadecimal MAC inputs all represent the same underlying six bytes.
For 00:1a:2b:3c:4d:5e, insertion produces 00:1a:2b:ff:fe:3c:4d:5e before the bit change. The modified identifier becomes 02:1a:2b:ff:fe:3c:4d:5e, yielding fe80::21a:2bff:fe3c:4d5e. A link-local IPv6 address only has meaning on its associated link, and operating systems often require a zone identifier when connecting to it. Modern SLAAC autoconfiguration can use stable or temporary privacy identifiers instead, so a valid derivation need not match the address a real device currently uses.
Understanding the 7th-Bit Inversion Rule (Universal/Local Bit)
Universal/local bit inversion is an XOR with hexadecimal 02 in the first byte. This is bit one when bits are numbered from the least significant end, or the seventh bit when counted from the most significant end. It is different from the multicast bit, which is the lowest bit. Confusing these positions changes the address incorrectly. The tool reports unicast or multicast separately from local or universal administration, and does not generate a usable link-local candidate for multicast or all-zero input.
The IEEE Organizationally Unique Identifier (OUI) is commonly the first three bytes of a globally administered MAC address. A prefix registration identifies an organization, not necessarily the final device manufacturer, owner, or model. This lookup includes only a small MA-L sample for popular vendors such as Apple, Cisco, Intel, Samsung, Huawei, Dell, TP-Link, Raspberry Pi, Netgear, and Espressif. Locally administered or randomized addresses cannot be attributed reliably by those first bytes. A missing dictionary entry means unknown here, not unregistered globally.
MAC and Modified EUI-64 Reference
| Stage | Example | Meaning |
|---|---|---|
| MAC | 00:1a:2b:3c:4d:5e | 48-bit input |
| Insert FFFE | 00:1a:2b:ff:fe:3c:4d:5e | 64-bit intermediate |
| Invert U/L | 02:1a:2b:ff:fe:3c:4d:5e | Modified interface identifier |
| Link-local | fe80::21a:2bff:fe3c:4d5e | 128-bit candidate |
| Cisco notation | 001a.2b3c.4d5e | Same original MAC |
Technical references
How to use MAC to IPv6 & OUI Vendor Lookup
1. Enter the input
Paste six hexadecimal MAC bytes using a single standard delimiter style, or enter twelve raw hexadecimal characters.
2. Inspect the local result
Review normalized notations, administration bits, and the local vendor-prefix match. A missing prefix is explicitly shown as unknown.
3. Apply the result carefully
Copy the modified EUI-64 candidate or desired MAC notation. Compare actual interface configuration before using the candidate in a network setting.
Key features and technical specifications
Local processing
Inputs stay in browser memory; no query or certificate is sent to a processing service.
Explicit limits
Results describe supplied data and bundled references, not live network measurements.
Use this result with its limits in mind
These tools transform supplied data locally. They do not scan devices, verify ownership, or confirm that a network service is secure.
Prepare configuration notes
Copy normalized values and check their meaning before applying a production change.
Learn protocol representations
Compare the examples and reference table with the interactive result.
Frequently asked questions
Why does EUI-64 insert FFFE in the middle?
The insertion expands a six-byte identifier to eight bytes in the defined modified EUI-64 construction. The universal/local bit is also inverted. Those eight bytes are an interface identifier, not an entire IPv6 address; the network prefix supplies the remaining bits.
What is an OUI?
An Organizationally Unique Identifier is an IEEE-assigned prefix used in identifiers such as some MAC addresses. This tool includes a small selection of 24-bit MA-L prefixes. IEEE also maintains other allocation sizes, so this sample is not a complete manufacturer database.
Why is my vendor listed as unknown?
The bundled sample covers only selected prefixes. A vendor can hold many assignments, and a virtual or randomized address may not carry a useful vendor prefix. Unknown is an honest absence of a match and is not evidence that your device is counterfeit or malicious.
Is the derived address my device’s actual IPv6 address?
Not necessarily. Privacy addressing, stable opaque identifiers, manual configuration, and operating-system policy can produce different addresses. The result is a mathematical candidate only. Check the interface configuration on the device to learn its actual link-local address and zone identifier.
Does copying another device’s MAC give me its identity?
No. A MAC is a link-layer identifier and can be changed or spoofed in some environments. The displayed vendor and derived address are not authentication or ownership evidence. Duplicate addresses can also disrupt a network, so use this converter for inspection and learning.