the dedicate a specific prefix for translation purposes. However, DHCPv6 PD was not available until 3GPP Release-10 and at that time the network should also have been fully dual-stack capable as well. 5.3.5 Bump-In-the-Host A BIH describes a tool where IPv4-only application inside a UE can talk to an IPv6-only destination with the help of UE-internal IPv4 to IPv6 protocol translation [34]. With this feature the BIH complements 464XLAT, as show in Table 5.4. The BIH supports two architectures for protocol translation. The first is socket Appli- cation Programming Interface (API) layer translation and the second is network layer translation. The architectural options are illustrated in Figure 5.10. In the socket API layer implementation option, the Function mapper translates IPv4 socket API calls made by an application to IPv6 API calls. In the network layer implementation option, the host implements Protocol translator at the network layer by using technologies more commonly used on routers: IP/ICMP translation defined in RFC 6145 [12], NAT64 defined in RFC 6146 [14], and DNS64 defined in RFC 6146 [26]. The protocol translation is supported by modules called Extension name resolver and Address mapper. The extension name resolver performs functions required to fetch IPv6 address from DNS even if the application requested only IPv4. This can include intercepting DNS queries as in the network layer model, or simply by intercepting socket API calls as in API-layer mode. The address mapper entity is responsible for creating local IPv4 address representations of destinations' IPv6 addresses, and maintaining mapping tables. The local addresses used by the address Deploying IPv6 in 3GPP Networks mapper are chosen from the private address space defined by RFC 1918 [25], as that is the only address space that applications are certain to understand as being address translated, and hence triggers applications to use NAT traversal techniques. The BIH comes with an inbuilt limitation to perform protocol translation only for IPv