ess assignment and configuration mechanisms available in 3GPP system. 3GPP supports both dynamically or statically assigned addresses and/or prefixes for each UE. Table 4.4 Available IPv4 and IPv6 address management and configuration methods in 3GPP IP version Method Remarks NAS signaling Mandatory and the most used. DHCPv4 Not commonly (ever) implemented in UEs or networks. IKEv2 For I-WLAN [103] & S2b untrusted non-3GPP access. MIPv4 Specification freak [20]. SLAAC Mandatory for IPv6. DSMIPv6 S2c (and H1 [104]) interfaces. IKEv2 I-WLAN [105] & S2b untrusted non-3GPP access [18]. DHCPv6 PD For mobile routers, not the UE itself. Deploying IPv6 in 3GPP Networks There are certain IP addressing related peculiarities and restrictions on 3GPP bearers. Some of them are inherent from the link model as discussed in Section 4.1.3. A PDN Connection can have a single IPv4, a single /64 IPv6 prefix or both. A UE may have multiple simultaneous active PDN Connections, which would make the UE essentially multi-interfaced. Each PDN Connection is typically represented as a network interface to the host IP stack. Prior to 3GPP Release-11, the IPv4 address that is assigned to a UE is always a /32. Since Release-11, the GTP-C signaling can also convey default gateway and subnet length information. These enhancements were needed to enable properly working DHCPv4 func- tionality for S2a Mobility based on GTP & WLAN access to EPC (SaMOG) [106] and unmodified end hosts with Institute of Electrical and Electronics Engineers (IEEE) 802.11 WLAN radio. In practice, /30 is the minimum workable subnet size for broadcast links such as the IEEE 802.11 WLAN. Four addresses are needed for the subnet address, default gateway on the same subnet, the end host address and the subnet broadcast address. Similarly to IPv4, the prefix length for IPv6 is fixed to /64 on the 3GPP link. Since 3GPP Release-10, DHCPv6 PD allows for assigning an IPv6 prefixes shorter than /64 to a UE (when acting as a mobile router or a tethering device). However, these shorte