n networks, is that the network should be always in control. There are a multitude of reasons for this principle. The reason for relatively strict network control is better qual- ity control (the network does not do anything unexpected), better scalability (the usage of the network resources for configuration can be minimized), and also control over charging and billing. However, as described earlier, compatibility for standard IP stacks, and the Internet has to be kept as well. Therefore, the configuration and address allocation in the 3GPP networks is designed be controlled by the network and the network operator. This means that the different con- figuration information, including UE's DNS server configuration and the IP addresses, are configured by the network. In IPv4 this was easy, as IPv4 was anyways lacking self-configuration mechanisms that later became available for IPv6. Without other con- figuration schemes in place, the network configures one single IPv4 address to the UE per Primary PDP Context, or default EPS Bearer. However, for IPv6 the network has to give more freedom and assign a range of addresses to the UE. We will describe this more detail in Section 4.4. However, despite this, the network always knows which UE has what IP address, and therefore can always map the IP address to a subscriber. Mobility Management and Network Infrastructure As discussed in Section 2.4, the purpose of mobility management is to make sure that the UE stays connected to the network and maintains service even when the UE is moving. The IP stacks, and IP networks, do not understand mobility very well. IP assumes that network links are relatively stable, and if they fail or change, the reasons are usually link failure, network detachment (as in cable detachment), or eventual network attachment to a different network. Therefore, the 3GPP technology almost completely hides mobility from the IP stack. This means that the IP address is kept the same during a session, and therefore, the UE is connected to the same IP netwo