Every DHCPv6 client has a DUID(DHCP unique identifier) that uniquely identifies the device. The DUID allows the clients and servers to identify each other. A DUID consists of a 2 byte code followed by a variable number of bytes that make up the actual identifier. A DUID can be no more than 128 octets long (not including the type code.
The DUID is designed to be unique across all DHCP clients and servers, and stable for any specific client or server - that is, the DUID used by a client or server SHOULD NOT change over time if at all possible; for example, a device's DUID should not change as a result of a change in the device's network hardware.[1]
Identity Association (IA) is a collection of addresses assigned to a client. Each IA has an associated IAID. A client may have more than one IA assigned to it; for example, one for each of its interfaces.
IAID(Identity association identifier) is an identifier for an IA, chosen by the client. EACH IA has an IAID, which is chosen to be unique among all IAIDs for IAs belonging to that client.[2]
