x assigned to the UE cannot be used for on- link determination (the 'L'-flag bit in the Prefix Information Option (PIO) in the Router Advertisement must always be set to zero). If the advertised prefix is used for SLAAC, then the 'A'-flag bit in the PIO must be set to one. Details of the 3GPP link-model and address configuration are provided in Section 11.2.1.3.2a of [25]. More specifically, the PGW guarantees that the /64 prefix is unique for the UE. Therefore, there is no need to perform any DAD on addresses that the UE creates (i.e. the DupAddrDetectTrans- mits variable in the UE could be zero). The PGW is not allowed to generate any globally unique IPv6 addresses for itself using the /64 IPv6 prefix advertised to the UE. The current 3GPP architecture limits the number of prefixes in each bearer to a single /64 IPv6 prefix. If the UE finds more than one prefix in the Router Advertisement, it only considers the first one and silently discards the others [25]. Therefore, multi-addressing within a single bearer is not really possible. Renumbering the previously advertised prefix without closing the layer-2 connection is also not possible. The lifetime of the /64 IPv6 prefix is bound to the lifetime of the layer-2 connection even if the advertised prefix lifetime is longer than the layer-2 connection lifetime. The advertised lifetimes (both valid lifetime and preferred lifetime) are always set to infinite (i.e., 0xffffffff). AAA Infrastructure When RADIUS (and Diameter likewise) is used on the (S)Gi-Interface, the external AAA server can assign an IPv6 prefix for a specific APN to a UE. Either the Framed-IPv6-Prefix attribute/AVP is used to convey the IPv6 prefix or alternatively the Framed-IPv6-Pool attribute/AVP is used to name the PGW internal IPv6 prefix pool in the Access-Accept/Authentication and/or Authorization Answer message. The IID is still selected by the PGW to the UE. However, the AAA server may affect the selection of the IID and return a specific IID value in the Framed-Interface-Id attribute/AVP i