Section: 6.2.4 IP address allocation 6.2.4.1 General
Content: This clause specifies IP address allocation for the PDU session. In this release of specification, PDU session can be initiated with one IP version, i.e. IPv4 PDU session type or IPv6 PDU session type, or with both IP versions, i.e. IPv4v6 PDU session type. IP address allocation to the UE shall be performed by SMF based on one or both the selected IP versions and operator policies. If IPv4 PDU session type is selected, an IPv4 address is allocated to the UE. If IPv6 PDU session type is selected, an IPv6 prefix except when the SMF acts according to subclause 6.2.4.3, and an interface identifier for the IPv6 link local address are allocated to the UE. If IPv4v6 PDU session type is selected, an IPv4 address, an IPv6 prefix except when the SMF acts according to subclause 6.2.4.3 or 6.2.4.4, and an interface identifier for the IPv6 link local address are allocated to the UE. If IPv6 or IPv4v6 PDU session type is selected in a PDU session established by the W-AGF acting on behalf of the FN-RG and the PDU SESSION ESTABLISHMENT REQUEST message contains the Suggested interface identifier IE, the SMF shall allocate to the UE the interface identifier for the IPv6 link local address indicated in the Suggested interface identifier IE. For IPv4 PDU session type and for IPv4v6 PDU session type, the UE: a) shall obtain an IPv4 address via: 1) NAS signalling as specified in subclause 6.2.4.2; or 2) DHCPv4 as specified in IETF RFC 2131 [33E]; and b) may obtain IPv4 configuration parameters (e.g. DNS server address) via DHCPv4 as specified in IETF RFC 2132 [33F] or may receive IPv4 configuration parameters (e.g. DNS server address) as specified in subclause 6.4.1 and subclause 6.3.2. For IPv6 PDU session type and for IPv4v6 PDU session type, the UE: a) shall build an IPv6 link local address based on the allocated interface identifier for the IPv6 link local address; b) shall obtain /64 IPv6 prefix via IPv6 stateless address autoconfiguration as specified in 3GPP TS 23.501[ System architecture for the 5G System (5GS) ]  [8] and IETF RFC 4862 [39], except when the 5G-RG or the W-AGF act according to subclause 6.2.4.3; c) may obtain IPv6 configuration parameters via stateless DHCPv6 as specified in IETF RFC 8415 [33D], except when the 5G-RG or the W-AGF act according to subclause 6.2.4.3, may receive IPv6 configuration parameters (e.g. DNS server address) as specified in subclause 6.4.1 and subclause 6.3.2, or may receive DNS server IPv6 addresses in a Router Advertisement Message as specified in IETF RFC 4861 [38B] with recursive DNS server option as specified in IETF RFC 8106 [52];and d) may obtain an additional IPv6 prefix for a PDU session by IPv6 prefix delegation via DHCPv6 as specified in subclause 6.2.4.2a.