Which used in the EUI-64 process to create an IPv6 interface ID on an IPv6 enabled interface?

The EUI-64 process creates an IPv6 interface ID by splitting a device’s MAC address and inserting “FFFE” in the middle. It also flips the 7th bit of the first byte. This method ensures unique IPv6 addresses. Learn more about IPv6 at Study4Pass, your trusted exam prep site.

Tech Professionals

15 April 2025

Cisco

Which used in the EUI-64 process to create an IPv6 interface ID on an IPv6 enabled interface?

Introduction

IPv6 is the next-generation Internet Protocol designed to replace IPv4, offering a vastly expanded address space, improved security, and simplified network configuration. One of the key aspects of IPv6 addressing is the Interface Identifier (ID), which uniquely identifies a device on a network. The EUI-64 (Extended Unique Identifier-64) process is a method used to automatically generate an IPv6 interface ID based on a device’s MAC address.

In this comprehensive guide, we will explore:

The structure of an IPv6 address
The role of the Interface ID
How the EUI-64 process works
Modifications made to the MAC address
Practical examples of EUI-64 in action
Advantages and limitations of EUI-64
Study resources for CCNA, CCDA, CCENT, and other certifications

For those preparing for Cisco certifications like CCNA (200-301), CCDA, CCENT, CCNA Security, or CCNA Wireless, understanding EUI-64 is crucial. Websites like Study4Pass provide excellent study materials, practice exams, and lab simulations to help you master these concepts efficiently.

IPv6 Address Structure

An IPv6 address is 128 bits long, compared to IPv4’s 32 bits, allowing for approximately 3.4 × 10³⁸ unique addresses. The IPv6 address is divided into two main parts:

Network Prefix (64 bits) – Identifies the network.
Interface ID (64 bits) – Identifies the host on the network.

The Interface ID can be:

Manually configured
Randomly generated (for privacy)
Automatically derived using EUI-64

What is EUI-64?

The EUI-64 (Extended Unique Identifier-64) process is a standardized method for generating a 64-bit Interface ID from a device’s 48-bit MAC address. This ensures globally unique IPv6 addresses without manual configuration.

Why Use EUI-64?

Automatic address configuration (useful in SLAAC - Stateless Address Autoconfiguration)
Globally unique Interface IDs (reduces address conflicts)
Consistency (helps in network management)

Steps in the EUI-64 Process

To convert a 48-bit MAC address into a 64-bit Interface ID, the following steps are taken:

Step 1: Split the MAC Address

A MAC address is 48 bits long, written in hexadecimal format (e.g., 00:1A:2B:3C:4D:5E).

Step 2: Insert FF-FE in the Middle

The MAC address is divided into two 24-bit halves, and FF-FE (0xFFFE in hex) is inserted in between.

Example:

Original MAC: 00:1A:2B:3C:4D:5E
After insertion: 00:1A:2B FF:FE 3C:4D:5E

Step 3: Flip the 7th Bit (Universal/Local Bit)

The 7th bit of the first byte (U/L bit) is inverted to indicate whether the address is globally unique (0) or locally administered (1).

Original first byte: 00 → 00000000 (binary)
Flip 7th bit: 00000010 → 02 (hex)

Final Modified First Byte: 02

Final EUI-64 Interface ID:
02:1A:2B:FF:FE:3C:4D:5E

Step 4: Combine with IPv6 Prefix

The 64-bit Interface ID is appended to a 64-bit IPv6 network prefix to form a complete IPv6 address.

Example:

Prefix: 2001:0DB8:ACAD::/64
Interface ID: 021A:2BFF:FE3C:4D5E
Full IPv6 Address: 2001:0DB8:ACAD:0000:021A:2BFF:FE3C:4D5E (or 2001:DB8:ACAD::021A:2BFF:FE3C:4D5E in compressed form)

Practical Example of EUI-64

Let’s take another MAC address and convert it using EUI-64:

MAC Address: AA:BB:CC:DD:EE:FF

Insert FF-FE:

Before: AA:BB:CC:DD:EE:FF
After: AA:BB:CC FF:FE DD:EE:FF

Flip the 7th bit:

First byte: AA → 10101010 (binary)
Flip 7th bit: 10101000 → A8 (hex)

Final Interface ID:
A8:BB:CC:FF:FE:DD:EE:FF

Complete IPv6 Address (with prefix 2001:DB8::/64):
2001:DB8::A8BB:CCFF:FEDD:EEFF

Advantages of EUI-64

Automatic Configuration: Reduces manual IP assignment errors.
Uniqueness: Ensures globally unique addresses.
Consistency: Helps in troubleshooting and network management.

Limitations of EUI-64

Privacy Concerns: Since the MAC address is embedded, it can be tracked.
Not Always Needed: Some networks use randomized Interface IDs for security.

EUI-64 in Cisco Devices

Cisco devices use EUI-64 for IPv6 autoconfiguration. To enable it:

Router(config)# interface GigabitEthernet0/0

Router(config-if)# ipv6 address 2001:DB8::/64 eui-64

This generates an IPv6 address with the EUI-64-derived Interface ID.

Study Resources for CCNA, CCDA, CCENT, and More

For those preparing for Cisco Certifications (CCNA 200-301, CCDA, CCENT, CCNA Security, CCNA Wireless), mastering IPv6 and EUI-64 is essential. Websites like Study4Pass offer:

Detailed Study Guides
Practice Exams
Hands-on Lab Simulations
Real-World Scenarios

By using Study4Pass, you can reinforce your understanding of EUI-64, IPv6 addressing, and other networking concepts with structured learning materials.

Conclusion

The EUI-64 process is a fundamental mechanism in IPv6 that automatically generates a 64-bit Interface ID from a device’s MAC address. By inserting FF-FE and flipping the 7th bit, it ensures globally unique IPv6 addresses without manual configuration.

For Cisco certification candidates, mastering EUI-64 is crucial for exams like CCNA (200-301), CCDA, CCENT, and CCNA Security. Platforms like Study4Pass provide excellent study materials to help you succeed in your networking career.

By understanding EUI-64, you can efficiently work with IPv6 addressing, automate network configurations, and troubleshoot IPv6 networks effectively.

Final Words

If you're preparing for Cisco exams, leverage Study4Pass for high-quality study materials, practice tests, and lab exercises to ensure success. Happy studying!