Cisco Certified Network Associate (CCNA) Practice Exam

How does the EUI-64 generate the Interface ID of an IPv6 address?

1. Inserts FFFE in the middle of the MAC address

2. Generates a random string

3. Uses only the last 6 digits of the MAC address

4. Removes the first byte of the MAC address

The correct answer is: Inserts FFFE in the middle of the MAC address

The process of generating an Interface ID for an IPv6 address using EUI-64 involves taking the 48-bit MAC address of a network interface. The correct approach is to split the MAC address into two halves and insert the hexadecimal value FFFE in between those two halves. This gives a 64-bit Interface ID that is unique to that interface. In more detail, when a MAC address is converted to an Interface ID, the first step is to take the 48-bit MAC address. The next step involves modifying the first byte of the MAC address to indicate whether the address is universally or locally administered. This modification is paired with inserting FFFE in the middle of the MAC address, effectively extending it to 64 bits. This method ensures that the resulting Interface ID is consistent and widely recognized, allowing devices to automatically generate their own addresses based on their hardware identifiers. By embedding FFFE, EUI-64 maintains compatibility and provides a reliable method for creating unique IPv6 addresses based on existing MAC addresses. This is why the insertion of FFFE in the middle of the MAC address stands as the correct answer.