t be given to the RRs (i.e. the UE) as such but has to be delivered by the DRs (i.e., the PGW) in such a way that the /64 prefix allocated to the default bearer (PDN Connection) is not part of the delegated prefix. An option to exclude a prefix from delegation [55] prevents this problem. Figure 4.21 illustrates an example deployment with an excluded prefix. Although endorsed by 3GPP specifications, the use of [55] is optional. However, the requirement to support aggregated prefixes is still mandatory. There are two alternative ways of solving the delegation issue without exclusions [55]. Firstly, the DHCPv6 server could only delegate one half of the prefix space allocated to the PDN Connection, and the /64 prefix for the UE would then be taken from the other half. From this other half, the rest of the prefixes are 'lost', and handled with a sink route. This is obviously a very wasteful use of prefixes. See a delegation example of this approach below: Prefix for the PDN Connection: 2001 : db8: : /56 Prefix allocated to the UE: 2001:db8:: /64 Prefix delegated to the UE: 2001:db8:0:80::/57 Prefixes with a sink route: 2001:db8:0:1::/64 to 2001:db8:0:7f::/64 Secondly, the delegated prefix could be cut into smaller 'subnets', and then delegated as a group of prefixes. While such (complex) approach is perfectly valid from an RFC PDN Network PDN Gateway (Delegating Router Mobile DHCPv6 Server) delegate Operator 2001:db8::/62 Network (2001:db8:0:0::/64 excluded) Bearer 2001:db8:0:0::1/64 UE Handset configured using SLAAC (Requesting Router DHCPv6 Client) 2001:db8:0:1::66 2001:db8:0:2::66 Subscriber Network 2001:db8:0:3::66 etc not yet assigned Figure 4.21 DHCPv6-based prefix delegation example and a tethering use case in 3GPP Release-10 networks. Deploying IPv6 in 3GPP Networks 3633 [27] point of view, it is assumed to be poorly supported by RRs. See a delegation example below: Prefix for the PDN Connection: 2001:db8::/56 Prefix allocated to the UE: 2001:db8::/64 Prefix 1 delegated to the UE: 2001:db8:0:80::/57 Prefix 2 d