EUI-64 Address Calculator from MAC Address


EUI-64 Address Calculator from MAC Address

An instant, accurate tool to calculate the Modified EUI-64 address required for IPv6 SLAAC from a standard 48-bit MAC address.


Enter a 48-bit MAC address. Formats like XX:XX:XX:XX:XX:XX, XX-XX-XX-XX-XX-XX, and XXXXXXXXXXXX are accepted.


Calculation Result:

Intermediate Values:

1. Original MAC-48:
2. Split and Insert ‘FFFE’:
3. Invert 7th Bit (U/L Bit):

What is an EUI-64 Address?

An Extended Unique Identifier (EUI-64) is a method used in IPv6 networking to automatically generate a unique 64-bit interface identifier from a device’s 48-bit MAC address. This process is a core component of IPv6 Stateless Address Autoconfiguration (SLAAC), which allows a device to join a network and assign itself a unique IPv6 address without needing a DHCP server. The goal is to leverage the globally unique MAC address provided by the hardware manufacturer to create a similarly unique interface ID for the IPv6 address.

While a standard MAC address is 48 bits, the IPv6 interface identifier is 64 bits. The EUI-64 process bridges this gap by defining a clear, reversible set of rules to expand the MAC address and ensure it conforms to IPv6 standards.

The Formula to calculate eui 64 address using mac address

The conversion from a 48-bit MAC address to a Modified EUI-64 interface ID follows three precise steps. This ensures a consistent and predictable outcome, which is crucial for network operations and troubleshooting. The process is designed to be computationally simple and reversible.

  1. Split the MAC Address and Insert ‘FFFE’: The 48-bit MAC address is divided into two 24-bit halves: the Organizationally Unique Identifier (OUI) and the NIC-specific part. The 16-bit hexadecimal value FFFE is inserted directly between these two halves. This expands the address from 48 to 64 bits.
  2. Invert the 7th Bit: The seventh bit from the left of the newly formed 64-bit address is flipped. This bit is known as the Universal/Local (U/L) bit. Inverting it changes its meaning from a manufacturer-assigned “universal” scope to a “local” scope, as required by the IPv6 standard.

Variables Table

Description of variables in the MAC to EUI-64 conversion.
Variable Meaning Unit / Format Typical Range
MAC-48 The original 48-bit hardware address. 6-octet Hexadecimal e.g., 00:1A:2B:3C:4D:5E
OUI Organizationally Unique Identifier (first half of MAC). 3-octet Hexadecimal e.g., 00:1A:2B
NIC Specific Device-specific identifier (second half of MAC). 3-octet Hexadecimal e.g., 3C:4D:5E
EUI-64 The final 64-bit interface identifier. 8-octet Hexadecimal e.g., 021A:2BFF:FE3C:4D5E

Practical Examples

Example 1: Standard MAC Address

  • Input MAC Address: 00:1A:2B:3C:4D:5E
  • Step 1 (Insert FFFE): The address is split into 00:1A:2B and 3C:4D:5E. Inserting FF:FE results in 00:1A:2B:FF:FE:3C:4D:5E.
  • Step 2 (Invert 7th Bit): The first octet is 00 (binary 00000000). Inverting the 7th bit (from 0 to 1) gives 00000010, which is 02 in hex.
  • Final EUI-64 Result: 02:1A:2B:FF:FE:3C:4D:5E

Example 2: MAC Address with a ‘1’ in the 7th bit position

  • Input MAC Address: C2:00:54:10:00:00
  • Step 1 (Insert FFFE): The address is split into C2:00:54 and 10:00:00. Inserting FF:FE results in C2:00:54:FF:FE:10:00:00.
  • Step 2 (Invert 7th Bit): The first octet is C2 (binary 11000010). Inverting the 7th bit (from 1 to 0) gives 11000000, which is C0 in hex.
  • Final EUI-64 Result: C0:00:54:FF:FE:10:00:00

How to Use This EUI-64 Calculator

  1. Enter the MAC Address: Type or paste the 48-bit MAC address into the input field. You can use colons, hyphens, or no separator.
  2. Click Calculate: Press the “Calculate” button to perform the conversion.
  3. Review the Results: The calculator will display the final EUI-64 address, highlighted for clarity.
  4. Analyze the Steps: Below the main result, you can see the intermediate values, showing exactly how the original MAC was transformed. This is useful for learning the process.
  5. Copy the Output: Use the “Copy Results” button to save the final EUI-64 address to your clipboard.

Key Factors and Concepts in EUI-64 Addressing

Understanding the EUI-64 process involves more than just the calculation; several key networking concepts are at play.

  • The Universal/Local (U/L) Bit: This is the 7th bit that gets inverted. Its original purpose is to distinguish between globally unique addresses (set to 0, assigned by IEEE) and locally administered addresses (set to 1). The inversion is a specific requirement of the IPv6 standard to prevent potential conflicts.
  • Stateless Address Autoconfiguration (SLAAC): EUI-64 is a primary mechanism for SLAAC. Devices listen for a network prefix from a router and then append their self-generated EUI-64 interface ID to create a complete, routable IPv6 address.
  • Uniqueness and MAC addresses: The entire system relies on the fact that MAC addresses, assigned by manufacturers, are globally unique. This uniqueness is transferred to the EUI-64 identifier.
  • Privacy Concerns: Because the EUI-64 address is directly tied to a device’s permanent MAC address, it can be used to track a device across different networks. This has led to the development of Privacy Extensions (RFC 4941), which generate temporary, random interface IDs instead.
  • ‘FFFE’ Infix: The hexadecimal value FFFE is reserved by the IEEE and is not supposed to appear in any assigned MAC address. Its presence in an EUI-64 address is a clear signal that the address was generated from a 48-bit MAC.
  • Reversibility: The EUI-64 process is easily reversible. By removing the ‘FFFE’ and flipping the 7th bit back to its original state, you can determine the original MAC address from the EUI-64 interface ID.

Frequently Asked Questions (FAQ)

Why do you need to calculate an EUI-64 address?

You need to calculate an EUI-64 address to determine the host portion of an IPv6 address when using SLAAC. It’s essential for network administrators to predict a device’s IPv6 address for firewall rules, access control, and troubleshooting.

Why is the 7th bit flipped?

The 7th bit (U/L bit) is flipped to signify that the address has been modified for local use within the IPv6 context. It differentiates the resulting Interface ID from the globally unique scope of the original MAC address, adhering to the rules set in the relevant RFCs.

What does the ‘FFFE’ in the middle mean?

The hexadecimal value FFFE is a reserved value inserted to expand the 48-bit MAC address to 64 bits. Its presence acts as a marker, indicating that the interface identifier was derived from a MAC address.

Is the EUI-64 process the only way to generate an IPv6 address?

No. Other methods include manual (static) configuration, stateful DHCPv6 (similar to DHCP in IPv4), and using randomly generated temporary addresses as defined by IPv6 Privacy Extensions.

Can I find the original MAC address from an EUI-64 address?

Yes. If you know an interface ID was generated using EUI-64, you can reverse the process: remove the ‘FFFE’ from the middle and flip the 7th bit of the first octet back to its original state.

Do all operating systems use EUI-64 by default?

No. While many network devices and Linux/macOS systems use EUI-64, modern versions of Windows (Vista and later) default to using random temporary interface IDs for privacy reasons.

What is the difference between MAC-48 and EUI-48?

Functionally, for the purpose of this calculation, they are the same. EUI-48 is the new terminology for the 48-bit address space that was traditionally known as MAC-48.

What’s a Link-Local Address?

A Link-Local address is an IPv6 address that is automatically configured on every interface and is used for communication only on the local network segment. It commonly starts with fe80:: followed by an interface identifier, which is often generated using the EUI-64 method.

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