on sections 5.4.2 and 5.4.3, do not require any particular transition pro- tocol support on UEs. For those transition tools that require explicit UE support, such as double translation described in Section 5.4.4, additional RFCs would be needed. Cur- rently it is a UE implementation specific decision what specific IPv6 transition tools, from the plethora that is available, are to be supported. The authors expect the IPv6 transition toolbox to settle during the coming years, and then the requirements will also clarify themselves. It is worth noting that RFCs are very often large documents that contain both mandatory and optional components. Whether optional components need to be supported or not IPv6 in 3GPP Networks Table 4.10 IPv6 RFCs needed by all 3GPP UEs Title Book Section Reference Path MTU Discovery 3.2.3 Internet Protocol Version 6 Extension Mechanisms for DNS (EDNSO) 3.10.2 [127] MLD for IPv6 3.2.4 [128] IPv6 Router Alert Option 3.2.2 [129] Source Address Selection for the MLD Protocol 3.2.4 [130] DNS Extensions to Support IP Version 6 3.10.2 [131] Uniform Resource Identifier (URI): Generic Syntax 3.9.3 [132] Default Router Preferences and More-Specific Routes 3.5.6 [133] Unique Local IPv6 Unicast Addresses 3.1.2 [134] IPv6 Addressing Architecture ICMP for the IPv6 [135] Neighbor Discovery for IPv6 IPv6 Stateless Address Autoconfiguration 3.5.1 Privacy Extensions for SLAAC 3.5.5 [109] Deprecation of Type 0 Routing Headers in IPv6 3.2.2 [136] Reserved IPv6 Interface Identifiers 3.5.1 [108] Handling of Overlapping IPv6 Fragments 3.2.3 [137] IPv6 Subnet Model 3.1.2 [138] A Recommendation for IPv6 Address Text Representation 3.1.9 [139] IPv6 RA Options for DNS Configuration 3.4.3 [140] Happy Eyeballs: Success with Dual-stack Hosts 3.9.4 [141] Default Address Selection for IPv6 3.5.4 [142] depends usually on what higher level features are going to be supported on a UE and sometimes on resource constraints. For example, if a 3GPP UE is strictly working on a host mode, it does not need to implement router-speci