 reply message to the LEASEQUERY request. This option contains the information requested about a host, which may be for example, the host's identifier, the host's IPv6 address, and a delegated prefix [78]. LEASEQUERY-DATA: A bulk leasequery mechanism has been defined to allow efficient queries that result in more than one response [79]. The LEASEQUERY-DATA message is used alongside LEASEQUERY-REPLY to transport additional responses. LEASEQUERY-DONE: The queried DHCPv6 server sends LEASEQUERY-DONE, when it has finished sending the bulk leasequery results [79]. DHCP Unique Identifier Each node implementing DHCPv6 must have a unique DHCP Unique IDentifier (DUID). The DUID is the identifier used by DHCPv6 clients and servers to uniquely identify each other over time [54]. The following four DUID types have been defined SO far: DUID Link-Layer address (DUID-LL): DUID based on a link-layer address only [54]. DUID Link-Layer address plus Time (DUID-LLT): DUID based on a link-layer address and time [54]. DUID vendor-assigned unique identifier based on Enterprise Number (DUID-EN): Vendor-assigned DUID to a device based on vendor's enterprise number [54]. DUID Universally Unique IDentifier (DUID-UUID): DUID based on Universally Unique IDentifier [80]. Implementations may use the DUID type that suits them best - the peers they commu- nicate with will only compare the values passed in these options. What is important is that nodes keep the DUID the same over time - SO that the DHCPv6 server sees a host as one, and not an ever-increasing number of hosts. DHCPv6 Prefix Delegation A node that forwards packets between its uplink and downlink network interfaces needs a way to number the downlink interfaces. The official tool for that in IPv6 is DHCPv6 PD [81]. The DHCPv6 client that requests prefixes with DHCPv6 PD is called a Requesting Router (RR) and the DHCPv6 server delegating the prefixes is called a Delegating Router (DR). What is important to notice is that the use of DHCPv6 PD is orthogonal to the method RR uses to confi