r Domain Name List option: A host implementing an IP Multimedia Subsystem (IMS) client can use this DHCPv6 option to find out a list of Proxy Call Session Control Function (P-CSCF)(s) domain names [87]. SIP Servers IPv6 Address List option: A host implementing an IMS client can use this DHCPv6 option to find out a list of P-CSCF(s) IPv6 addresses [87]. Option Request option: A host indicates to a server DHCPv6 options it wishes to receive by listing the option codes in the Option Request option [54]. Identity Association for PD option (IA_PD): A host performing RR functionality includes the IA_PD option to indicate its identity. This option can include other options, such as an IA_PD Prefix option [81]. IA_PD Prefix option: This option is transported inside an IA_PD option to communicate a prefix delegated to RR [81]. Prefix Exclude option: This option communicates a portion of a prefix on an IA_PD Prefix option that is excluded, and that must not be used by an RR for numbering the RR's downlink network [82]. The excluded prefix may be used on the RR's uplink, as is a case with 3GPP. Information Refresh Time option: This option specifies an upper bound for the time after a client should refresh the information it has received from DHCPv6 [84]. Server Unicast option: DHCPv6 server uses this option to indicate to the DHCPv6 client that it is allowed to send unicast messages to this DHCPv6 server [54]. Port Control Protocol (PCP) Server Name option: This option communicates a PCP server's domain name (see Section 6.4.3). At the time of writing, the option is still under standardization by the IETF [88]. Address Selection option: This option communicates site-specific address selection policies. The option is under standardization by the IETF [89]. 3.5.3 IKEv2 Even though Internet Key Exchange version 2 (IKEv2) is, as the name suggests, designed for key management (see Section 3.8.3), it also supports single /128-bit IPv6 address configuration [90]. Unfortunately, in the standard track IKEv2 RFC 5996 the IPv6 support