gure addresses for its uplink interface. This means that RR may have its uplink configured with link-local addresses only, addresses configured with SLAAC, or addresses configured with DHCPv6. The prefix delegation works by the RR sending a DHCPv6 SOLICIT message with an Identity Association for Prefix Delegation (IA_PD) option. DRs that could delegate prefixes to the requester then respond with a DHCPv6 ADVERTISE message. The RR Introduction to IPv6 /56 prefix Routes: for local use 1) /64 for link 2) /56 towards RR Case A) Requesting Delegating Router Router Case B) (/56 - /64) prefix Routes: for local use 1) /56 towards RR Figure 3.16 Example of DHCPv6 PD (case A) and DHCPv6 PD Exclude Option (case B). chooses the DR it wishes to use, and sends the DHCPv6 REQUEST message, which DR replies with prefixes and possibly other information. After the successful message exchange, the network will start routing packets destined to the delegated prefix to the RR. Case A of Figure 3.16 illustrates the basic DHCPv6 PD in action: the DR has allocated a /64 prefix for the link between it and the RR. The DR has also delegated a /56 prefix for the RR, which the RR may utilize for numbering downlink Local Area Networks (LANs). Case A illustrates also how the DR has two routes towards one RR. This example of case A is based on fixed-network architecture where the link, such as a Virtual Local Area Network (VLAN), between RR and DR is numbered with global addresses. In some deployments, the link between RR and DR could be numbered with just link-local addresses, in which case the example's DR would only have one route. In some networks, a special extension for PD is needed due to addressing limitations on said networks. An option called DHCPv6 PD Exclude Option may be used to exclude a prefix out from the delegated prefix, as defined in RFC 6603 [82]. The prefix that is excluded is commonly the prefix gateway (which may or may not be the DR) uses in the Router Advertisements sent to the link towards the RR and that may be used by