EUI-64 Calculator: Convert MAC to IPv6 Address
The EUI-64 calculator converts any 48-bit MAC address into a 64-bit interface identifier for IPv6 addressing. This process, defined in RFC 4291, is fundamental to Stateless Address Autoconfiguration (SLAAC) and is a critical concept for CCNA and CCNP certification exams. Our tool provides both the final IPv6 address and a complete visual breakdown so you can see exactly how each transformation step works at the bit level. For general subnet calculations, visit our subnet calculator or CIDR calculator.
What Is an EUI-64 Interface ID?
An EUI-64 (Extended Unique Identifier 64) interface identifier is a 64-bit value that identifies a network interface on an IPv6 network. It is derived from a device's 48-bit MAC address through a three-step transformation: splitting the MAC into two 24-bit halves (OUI and NIC), inserting the 16-bit value FF:FE between them, and flipping the 7th bit of the first byte. The result is a 64-bit identifier that serves as the host portion of an IPv6 address. This mechanism allows devices to automatically configure their own IPv6 addresses without needing a DHCP server—a process known as SLAAC.
For example, a MAC address of 00:1A:2B:3C:4D:5E becomes the EUI-64 interface ID 021a:2bff:fe3c:4d5e, which can be combined with a link-local prefix to form fe80::21a:2bff:fe3c:4d5e or with any global /64 prefix for global unicast addressing. The EUI-64 format is standardized in IEEE and provides a deterministic, globally unique interface identifier that eliminates address conflicts on the same network segment. For IPv4 to IPv6 translation, see our IPv4 to IPv6 calculator.
Why Do We Flip the 7th Bit (U/L Bit)?
The 7th bit of the first byte in a MAC address is known as the U/L bit (Universal/Local bit). In the original MAC address, this bit is set to 0 to indicate that the Organizationally Unique Identifier (OUI) is globally unique and assigned by the IEEE. When converting to EUI-64 for IPv6, this bit is flipped to 1 to indicate that the resulting interface identifier is locally administered rather than globally unique. This distinction is important because the EUI-64 identifier was generated algorithmically rather than being a hardware-assigned address.
The bit flip also serves as a practical security mechanism. By flipping the U/L bit, IPv6 addresses derived from MAC addresses cannot be directly traced back to the manufacturer's OUI without reverse calculation. This provides some level of privacy, though it is not sufficient for anonymity. RFC 4941 (Privacy Extensions for SLAAC) addresses this further by generating temporary random interface IDs that change over time.
From a CCNA exam perspective, the 7th bit flip is one of the most frequently tested IPv6 concepts. You should remember that flipping the 7th bit is equivalent to XORing the first byte with 0x02. For example, 0x00 becomes 0x02, 0x12 becomes 0x10, and 0xFC becomes 0xFE. Our calculator shows this transformation visually in the bitwise breakdown matrix, making it easy to verify your exam calculations.
How to Use the MAC to IPv6 Link-Local Converter
Using this EUI-64 interface ID converter is straightforward. Enter any valid MAC address in any common format (colon-separated, hyphenated, Cisco dotted, or raw hex) and the tool instantly generates the corresponding IPv6 link-local address and EUI-64 interface ID. If you have a specific global unicast prefix, enter it in the optional prefix field to get a complete global IPv6 address. The tool accepts prefixes in standard IPv6 notation, with or without the /64 length.
The step-by-step breakdown panel shows each phase of the conversion: the MAC split into OUI and NIC halves, the insertion of FF:FE, the binary bit flip matrix for the first byte, and the final IPv6 address assembly with zero compression applied. This visual approach makes the EUI-64 conversion process intuitive for networking students studying for CCNA, CCNP, or cloud networking certifications. Whether you are configuring IPv6 on Cisco routers, AWS VPCs, or Azure virtual networks, understanding EUI-64 is essential for modern network engineering.
Common CCNA Exam Questions on EUI-64
CCNA and CCNP exams frequently test EUI-64 conversion with questions like: "Given a MAC address of 0050.7966.6800, what is the modified EUI-64 interface identifier?" or "What is the link-local address derived from MAC 00:1C:10:2A:3B:4D?" The key steps to remember are: (1) split the MAC into two 24-bit halves, (2) insert FF:FE in the middle, (3) flip the 7th bit of the first byte by XORing with 0x02, and (4) format the result as four 16-bit hexadecimal groups separated by colons.
Another common question type asks about the U/L bit: "Which bit in the EUI-64 interface identifier indicates whether the address is globally unique or locally administered?" The answer is the 7th bit of the first byte (the U/L bit). A value of 0 means globally unique (IEEE assigned), while a value of 1 means locally administered. This bit is flipped during the EUI-64 conversion process to signal that the address was algorithmically generated.
For cloud networking certifications (AWS Advanced Networking, Azure Network Engineer), understanding EUI-64 helps you troubleshoot IPv6 configuration issues in VPC subnets, virtual network gateways, and load balancers. Our MAC to IPv6 link-local converter serves as a practical study aid and reference tool that you can bookmark for exam preparation and real-world network configuration.