fic features. 4.7.3 DNS Issues Partly due to the colorful history of RDNSS discovery, the 3GPP system includes passing of the recursive DNS server addresses as part of PCO information element signaling. Furthermore, the 3GPP specifications allow the use of stateless DHCPv6 for passing the information. At the time of writing, the 3GPP does not formally support a Router Advertisement-based approach. For UEs it is theoretically enough to support only the PCO information element based approach, and currently that is supported in all 3GPP deployments that support IPv6. However, as UEs usually also support other access technologies where both DHCPv6 and Router Advertisement approaches are used, it is wise to also support these approaches in 3GPP interfaces - as a backup solution and for future extensibility, if for no other reason. A large UE population supporting the IP-layer approaches would enable simplification of the 3GPP architecture and hence perhaps removal of the PCO information element based method - in the distant future. Deploying IPv6 in 3GPP Networks Table 4.11 IPv6 optional RFCs for 3GPP UEs Title Book Section Reference Transmission of IPv6 Packets over Ethernet Networks [143] IPv6 Jumbograms 3.2.3 [144] Extensions to IPv6 ND for Inverse Discovery Spec. 3.4.4 [145] DHCPv6 for IPv6 3.5.2 DNS Configuration options for DHCPv6 3.10.2 Stateless DHCPv6 3.5.2 MLDv2 for IPv6 3.2.4 SEcure Neighbor Discovery (SEND) 3.4.9 [146] Cryptographically Generated Addresses (CGA) 3.4.2 [147] Information Refresh Time Option for DHCPv6 3.5.2 [148] Optimistic Duplicate Address Detection (DAD) for IPv6 3.4.7 [149] Using IGMPv3 and MLDv2 for SSM 3.2.4 Source-Specific Multicast for IP 3.2.4 Packetization Layer Path MTU Discovery 3.2.3 Extended ICMP to Support Multi-Part Messages [150] IP Version 6 over PPP IPv6 Router Advertisement Flags Option 3.4.3 [151] Lightweight IGMPv3 and MLDv2 Protocols 3.2.4 [152] Extending ICMP for i/f and Next-Hop Identification [153] Address Mapping of IPv6 Multicast Packets on Ethernet 3.6.2 [154] IP