In DHCPv6, what identifier is used to uniquely identify clients?

• A. DUID - DHCP Unique Identifier
• B. MAC Address
• C. IP Address
• D. Hostname

Answer: (A)

DHCPv6 identifies a client with a DUID, the DHCP Unique Identifier. This provides a stable, globally unique identity for the client in DHCPv6 exchanges, so the server can recognize the same client across different network segments and sessions. A MAC address isn’t reliable for identification in DHCPv6 because hardware addresses can change (virtual machines, privacy extensions, or migration), and an IP address is assigned and may change as the client moves or reconfigures. A hostname is just a human-friendly label and not the protocol’s method for consistently identifying a client. The DUID comes in various formats (such as including the link-layer address and time, an enterprise-number-based identifier, or a UUID), but the key point is that it uniquely identifies the client within DHCPv6. For multi-interface clients, the DUID is used alongside the IAID to distinguish each interface’s identity, ensuring precise tracking of each network interface’s DHCP state.