Which DUID type is generally used if the network interface is permanent or unchangeable, similar to using the MAC address?

• A. DUID-LLT
• B. DUID-EN
• C. DUID-LL
• D. DUID-UUID

Answer: (C)

Use the DUID that is based on the Link-Layer address. This format includes only the hardware (MAC) address and the Ethernet type, so the identifier stays the same as long as the NIC remains unchanged. That stability mirrors using the MAC for a permanent, unchangeable interface, ensuring the DHCPv6 client is consistently identified across reboots and sessions.

The other formats introduce elements that can vary or are not tied directly to the NIC. DUID-LLT adds a timestamp, which makes the DUID change when you boot or the time component updates, not ideal for a permanent interface. DUID-EN relies on an enterprise-assigned identifier, which is more specialized and not universally tied to the device’s NIC. DUID-UUID is based on a UUID, which is not inherently linked to the MAC and can be more cumbersome to manage in typical environments.